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Natural Science Forum / Physics / Acoustics / January 2006how your ears work
Inside the cochlea of a human ear are hundreds of thin cilia. Rather like an insect's eye, which is made up of hundreds of very primitive eyes, each cilium responds individually to the pressure variations in the cochlear fluid caused by sounds, contributing its own primitive interpretation of the sound to the overall picture. Each cilium responds to pressure by firing a synapse and sending a bio-electrical signal along the aural nerve into the inner brain, the journey along the aural nerve taking about a 25th of a second. While a 25th of a second's worth of pressure variation information is on the aural nerve, the brain attempts to match its auditory memory with features in the pressure variation information. Neural pathways into the brain's memory of pressure variation patterns are strengthened during this process, resulting in the brain deciding on what the sound 'is'. Sounds good to me.... I gave this much thought and I can find no fault with it. > Inside the cochlea of a human ear are hundreds of thin cilia. Rather > like an insect's eye, which is made up of hundreds of very primitive [quoted text clipped - 9 lines] > memory of pressure variation patterns are strengthened during this > process, resulting in the brain deciding on what the sound 'is'. If you're really interested in this and want to read more, I found this pretty fascinating: http://www.maths.abdn.ac.uk/~bensondj/html/maths-music.html The best current book on this subject is "Music, The Brain and Ecstacy: How Music Captures Our Imagination" by Robert Jourdain (Morrow, 1997). (No, not the drug ecstacy, you silly youts.) Jourdain follows the theme from anatomy to neurophysiology and brain structure to psychology and musical learning. It's a real good book, dense but well worth the effort. My only problem is that Jourdain is a DWEM supremacist and that colors his science writing just a bit.... but the only way to see what I'm talking about is to read his arguments on tone perception. Good resource for synthesists. so what 'is' a sound? > Inside the cochlea of a human ear are hundreds of thin cilia. Rather > like an insect's eye, which is made up of hundreds of very primitive [quoted text clipped - 9 lines] > memory of pressure variation patterns are strengthened during this > process, resulting in the brain deciding on what the sound 'is'. p...@aol.com wrote: so what 'is' a sound? maes...@ultrapiano.com wrote: > Inside the cochlea of a human ear are hundreds of thin cilia. Rather > like an insect's eye, which is made up of hundreds of very primitive [quoted text clipped - 9 lines] > memory of pressure variation patterns are strengthened during this > process, resulting in the brain deciding on what the sound 'is'. >From the brain's point of view a sound 'is' approaching from the left, for example, or a sound 'is' running water, or 'is' frightening, or pleasant. The brain can detect such qualities without thought, because of automatic biologically evolved processes occuring within it, such as comparison of remembered pressure variation patterns with those in the sound. Sound can be described mathematically as consisting of sinewaves at different frequencies and amplitudes, or as the numbers in a .wav or .mp3 file, but the information on the aural nerve is none of these. Each cilia fires when sufficient pressure above the ambient has been applied, and then takes about a 10th of a second to recover so that it is ready to fire again (by which time the internal pressure in the cochlea will usually have decreased to below the ambient for a short while). Some cilia are less responsive than others and take more time to recover, but each cilium individually behaves like a very primitive ear, which becomes dormant for a short while whenever it has been squashed by the pressure in the ear sufficiently for its synapse to fire. The hundreds of cilia individually send their primitive information along the aural nerve to the inner brain, and the brain can interpret the total of the sound information corresponding to a 25th of a second while it is on the aural nerve. A loud sudden sound would probably cause a lot of cilia to fire simultaneously, along with low-level echoes, and the brain can detect that pattern of information as it travels along the nerve fibres. High frequency sound might result in the frequent occurrence of large numbers of cilia firing in a short period of time, corresponding to a short length of the aural nerve on which the pattern is occurring. The often-repeated belief (sometimes called the travelling wave theory) that the ear itself hears sound mechanically (rather than the brain doing the hearing and deciding on what a sound 'is'), with each cilium tuned by nature to respond to a specific sinewave frequency, and vibrating sympathetically to 'sound waves' of that frequency because of resonance effects in the cochlear fluid, and the basilar membrane detecting the strength of the vibration (rather like the base of a cat's whisker) to give the amplitude of a frequency, is basically quite ridiculous and should be abandoned. Is there a better theory? I think pretty much all of the physiology of hearing is based on this "oft-repeated belief." What exactly do you find wrong with it? >Is there a better theory? I think pretty much all of the physiology of >hearing is based on this "oft-repeated belief." The oft-repeated-belief that each hair cell resonates a particular frequency and that it interprets sound mechanically, rather than sound being interpreted by the brain, leads to very definite predictions about how each should behave under experimental conditions. >What exactly do you find wrong with it? Since it leads to predictions, it's fine as a historical scientific hypothesis. Since those predictions have repeatedly, consistently turned out to be wrong, it's not a hypothesis worthy of any further serious consideration. As a scientific theory, it has failed, gloriously. Science moves on.  SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ Wow, now there are two of you; this is interesting. So what you're saying is that, according to the popular opinion, each frequency component stimulates certain hair cells, and those cells in turn interpret the sound and identify it to the brain? I have never heard of this theory before. It was my impression that each cell responds to a particular frequency component and relays the presence or absence of that component to the brain, and that the brain interprets the whole set of sensations. This seems to be the jist of the few anatomy diagrams and articles I found in a brief internet search. It also agrees with high school physics. What predictions and studies are you referring to? >Wow, now there are two of you; this is interesting. > [quoted text clipped - 6 lines] >component and relays the presence or absence of that component to the >brain, Bingo, same thing as we were just saying, and dead wrong. > and that the brain interprets the whole set of sensations. This >seems to be the jist of the few anatomy diagrams and articles I found >in a brief internet search. It also agrees with high school physics. High school physics barely prepares you for real acoustics much less cellular dynamics. >What predictions and studies are you referring to? That the loss of a specific cell or neighborhood of cells can be mapped to deafness at a specific frequency but not around it, for instance. Doesn't work. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ > High school physics barely prepares you for real acoustics much less > cellular dynamics. I have the feeling that quantum physics is in the picture. That is, the hair cells frequency response is limited to a certain increments that are quantized. Another approach is that the "harmonicity" of note pairs is limited by the speed at which the brain can process the incoming nerve impulses emitted from the cochlea. When the two notes are close enough together in frequency, their difference frequency will be resolved, and the resulting perceived "beat" effect makes the sensation unpleasant. On that basins, "beats" or difference frequencies must be high enough (e.g. 40 Hz or more) so as not to be perceived as modulations. Now, the effect of pleasure seems to be evoked by particular note frequency pairs whose ratio is expressed by small whole numbers. I can't think beyond that point. Angelo Campanella >> High school physics barely prepares you for real acoustics much less >> cellular dynamics. > >I have the feeling that quantum physics is in the picture. That is, the No. It's just as simple as that the cochlea is NOT a physical Fourrier transform, with low frequencies sensed at one and and high frequencies sensed at the other end. It's a long conch-shell-shaped resonator full of feelers, and different frequency components will stimulate parts in different patterns, but the interpretation to an approximation of a Fourrier transform in brain cells happens in nerve cells, mostly in the brain itself. The smallest actor worth considering in the picture is still a nerve cell, something millions of times bigger than a neurotransmitter molecule, and gazillions of times larger than anything where quantum dynamics is an issue. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ What the original "how your ears work" ( http://ultrapiano.com/manufacturers/EarPage.jpg ) is getting at is that the ear and brain do not perform spectral analysis of sound at all! The hair cells are not tuned to specific frequencies, but simply transmit a nerve impulse onto the aural nerve when they have been squashed by pressure in the cochlea. Because of the large number of hair-cells individually sending nerve impulses, patterns of impulses occur on the aural nerve. These patterns of pressure variations are recognised by the inner brain while they are on the aural nerve. From this simple information we recognise human speech and can distinguish between words and understand its emotional content. > > High school physics barely prepares you for real acoustics much less > > cellular dynamics. [quoted text clipped - 17 lines] > > Angelo Campanella >What the original "how your ears work" ( >http://ultrapiano.com/manufacturers/EarPage.jpg ) is getting at is that [quoted text clipped - 7 lines] >information we recognise human speech and can distinguish between words >and understand its emotional content. Okay, but the frequencies of simple sine waves do have high corrolation with specific columns of brain tissue being excited. How exactly this corrolation arrises is good for some research, but it isn't done in any simple straightforward way by the cochlea. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ > What the original "how your ears work" ( > http://ultrapiano.com/manufacturers/EarPage.jpg ) is getting at is that > the ear and brain do not perform spectral analysis of sound at all! Ok. I had to take a look at the text. It does not say that the ear and the brain do not perform spectral analysis. It says that the information in the auditory nerve is not a mere spectral analysis of sound, which is very much true. However, the neural impulses travelling through the auditory nerve *include* information about the spectral content of sound, and that information is used by the brain. No doubt about that. >> What the original "how your ears work" ( >> http://ultrapiano.com/manufacturers/EarPage.jpg ) is getting at is that [quoted text clipped - 6 lines] >auditory nerve *include* information about the spectral content of >sound, and that information is used by the brain. No doubt about that. Or at least some sort of information from which spectral information can be estimated. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ >>> What the original "how your ears work" ( >>> http://ultrapiano.com/manufacturers/EarPage.jpg ) is getting at is that [quoted text clipped - 8 lines] > Or at least some sort of information from which spectral information > can be estimated. Does this not imply that the ear/brain could match sounds based partially on their containing Fourier components higher in frequency than what they can detect as pure sinusoids (the way hearing bandwidth and sensitivity are commonly measured)? Bob Signature"Things should be described as simply as possible, but no simpler." A. Einstein >>>> What the original "how your ears work" ( >>>> http://ultrapiano.com/manufacturers/EarPage.jpg ) is getting at is that [quoted text clipped - 13 lines] >than what they can detect as pure sinusoids (the way hearing bandwidth >and sensitivity are commonly measured)? No. If you'd like to explain how you got there, let us know. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ >> Does this not imply that the ear/brain could match sounds based >> partially on their containing Fourier components higher in frequency >> than what they can detect as pure sinusoids (the way hearing bandwidth >> and sensitivity are commonly measured)? > > No. If you'd like to explain how you got there, let us know. Were there no intrinisc decomposition by frequency at the ear, just an associative mechanism that matches learned patterns of cochlear excitation with semantics, then one might not hear a high frequency sinusoid whose presence as a Fourier component might be necessary to make a match with something learned. Bob Signature"Things should be described as simply as possible, but no simpler." A. Einstein >>> Does this not imply that the ear/brain could match sounds based >>> partially on their containing Fourier components higher in frequency [quoted text clipped - 6 lines] >associative mechanism that matches learned patterns of cochlear >excitation with semantics, Very odd sort of bifurcation. The decomposition is in the brain, not the ear. The associative pattern-matching is in a different section of the brain. > then one might not hear a high frequency >sinusoid whose presence as a Fourier component might be necessary to >make a match with something learned. Logic derived from a bifurcation is only as good as the evidence showing that no other cases deserve consideration. In this case, a third case has long since been established. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ >>>> Does this not imply that the ear/brain could match sounds based >>>> partially on their containing Fourier components higher in frequency [quoted text clipped - 7 lines] > Very odd sort of bifurcation. > The decomposition is in the brain, not the ear. So you think that decomposition by frequency is done by a neural structure predicated by the genes? I.e., it is standard equipment and not built by experience? > The associative pattern-matching is in a different section of the brain. > [quoted text clipped - 5 lines] > showing that no other cases deserve consideration. In this case, > a third case has long since been established. I have no idea what you are talking about. Bob Signature"Things should be described as simply as possible, but no simpler." A. Einstein >>>>> Does this not imply that the ear/brain could match sounds based >>>>> partially on their containing Fourier components higher in frequency [quoted text clipped - 11 lines] >structure predicated by the genes? I.e., it is standard equipment and >not built by experience? Yes. But it's not done in the cochlea, and there's no requirement for it to be anywhere as straightforward a thing as a Fourrier transform. >> The associative pattern-matching is in a different section of the brain. >> [quoted text clipped - 7 lines] > >I have no idea what you are talking about. The third case is that a frequency-corrolated neurology has been established to exist hardwired, but it's not in the cochlea. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ > >> What the original "how your ears work" ( > >> http://ultrapiano.com/manufacturers/EarPage.jpg ) is getting at is that [quoted text clipped - 9 lines] > Or at least some sort of information from which spectral information > can be estimated. Yes, of course the information that spectral analysis gives, is contained in the electrical impulses that the ear sends along the aural nerve into the brain. The information contained by the numbers in a .wav or .mp3 file is also contained in the same electrical impulses, but it is pointless to mention that as anything to do with what the brain does with the pressure variation information that it receives - spectral content is similarly irrelevant. It is also true that experiments have been performed with sinewave inputs to the ear, which cause indentifiable hair-cells to fire. However, these experiments do not claim to prove that specific hair-cells encode specific frequencies, but unfortunately they do not disprove it either. The hair-cells are all fairly similar, although the ones at the centre of the spiral cochlea are somewhat shorter and stubbier than the ones at the other end of the spiral. The only difference between them biologically is that the shorter haircells take more pressure before they fire their synapse, and also take longer to recover before they can fire again, than the longer ones. Because of that, each individual hair-cell must be responsive to all audible frequencies at any amplitude, but some are more responsive than others. The ear/brain is actually tuned 'by nature' to hear and understand human speech, and is particularly good at identifying the tiny nuances which give the emotional content and indicate the speaker's state of mind. The ups and downs in pitch and the changes in loudness during normal speech are all part of what the brain recognises when it hears a voice, but does anyone suggest that the ear is encoding these important parts of spoken sound at the hair-cell level? Of course not, the hair-like structures have not evolved to detect 'ups' or 'downs' in the voice of a potential mate - so why should anyone take seriously the idea that the ear performs a spectral analysis of human speech - what evolutionary advantage would it give? If someone had only ever heard their parents talking, and had never heard sinewaves before, if you played a sinewave (440Hz from a tuning-fork A, for example) they would at first say that the tuning fork sounded like their mother or father, until they had learned that the new sound was a different thing. The ability to identify sinewaves is a learnt ability, and is not evolved by nature. I think that most theorists are confusing themselves with the idea of building an 'artifical ear' that can hear by itself, which could be perhaps plugged into the brain to cure deafness. Human ears don't hear - they channel air pressure variations into the cochlea. The hair-cells transduce these pressure variations into electrical impulses which travel along the aural nerve. The aural nerve acts as a delay line, containing about a 25th of a second's worth of information at any one time. The brain matches features and patterns in the information on the aural nerve against remembered information patterns (from previously heard sounds) to produce the sensation of hearing. > I think that most theorists are confusing themselves with the idea of > building an 'artifical ear' that can hear by itself, which could be > perhaps plugged into the brain to cure deafness. I don't know any theorist who would claim things are that simple. > Human ears don't hear > - they channel air pressure variations into the cochlea. The > hair-cells transduce these pressure variations into electrical impulses > which travel along the aural nerve. This reminded me of cochlear implants which exist and work. The implants transduce the sound arriving to the ears to electrical pulses that stimulate the auditory nerve. A deaf child receiving such an implant will learn to hear (although not as well as with normal hearing) and speak. However, an adult might not learn to understand speech unless deafened after learning the ability naturally. > The aural nerve acts as a delay > line, containing about a 25th of a second's worth of information at any > one time. The auditory nerve does not preserve any information. True, it takes a finite time for the sound to travel through the nerve, but the brain cannot sample what is in the middle. 25th of a second sounds like a time when the information is well beyond the auditory nerve but has not reached the cortex, yet. At these intermediate stages some past information is available. > The brain matches features and patterns in the information > on the aural nerve against remembered information patterns (from > previously heard sounds) to produce the sensation of hearing. On this I can agree. > > I think that most theorists are confusing themselves with the idea of > > building an 'artifical ear' that can hear by itself, which could be > > perhaps plugged into the brain to cure deafness. > > I don't know any theorist who would claim things are that simple. By 'theorists' I include 'conspiracy theorists', who claim that brain research has reached the stage where governments control us all with mind implants etc. - I think they are confused. > > Human ears don't hear > > - they channel air pressure variations into the cochlea. The [quoted text clipped - 15 lines] > > On this I can agree. The explanation I gave is of necessity simplified, and I hope the simplified terminology I used is not too misleading. I was calling the hair-cells 'cilia' until someone wrote and told me that that is how researchers refer to the 'spirocilia', which are little tufts of tiny hairs at the end of each hair-cell - in the literature, these are apparently sometimes confused with the organ of Corti, which in turn is sometimes confused with the basilar membrane. Sometimes, pictures of the 'rods and cones' in the eye have been displayed on internet websites and labelled as pictures of the ear's 'cilia'. You may well be right, that the auditory nerve only holds information temporarily, that the brain "cannot sample what is in the middle" [of the auditory nerve], and that after a 25th of a second any information from the ear will have travelled beyond the auditory nerve towards the auditory cortex. The explanation I gave is still essentially correct, however, in that the brain keeps about a 25th of a second's worth of input sound pressure information at any one time, on a delay-line principle. The information does not necessarily all have to be on the auditory nerve, but can be spread out, beyond what you might define as the end of the auditory nerve, into the neural pathways which extend further into the brain. We do of course have two ears, and the brain is split into left and right halves, connected by a thick bundle of fibres for communication between the two halves. When hearing, the most basic function performed by the brain, is comparison of the information from the left and right ear to detect where a sound is coming from, and at the same time the brain tries to match this information with previously heard sounds to identify what it is hearing. The left brain handles the information from the right ear, and vice versa. It is not unreasonable to suppose that the brain preserves both versions of the information it hears, to make subsequent matching more efficient. Count your blessings, o ye with decent hearing and cool toys. http://www.wired.com/wired/archive/13.11/bolero.html -- HellPope Huey Mr. Ed is a minion of Satan, horses can't TALK! Run, Wilbur, RUN! It is never too late to be what you might have been. ~ George Eliot And a man who comes back from the dead has a story to tell. ~ Dave Roever, "Welcome Home, Davey" Fresh sonic vittles @: http://www.beat-factory.net/hellpope/ > Count your blessings, o ye with decent hearing and cool toys. > > http://www.wired.com/wired/archive/13.11/bolero.html http://www.wired.com/wired/archive/13.11/ear.html (Reprogramming the Inner Ear) > HellPope Huey > Mr. Ed is a minion of Satan, horses can't TALK! [quoted text clipped - 10 lines] > Fresh sonic vittles @: > http://www.beat-factory.net/hellpope/ sci.physics Re: Synthetic Telepathy and Tachyons Raktizer Omheit wrote: > The Pentagon and the U.S. intelligence agencies called the N.S.A. [ National > Security Agency ], C.S.S. [ Central Security Service ], D.I.A. [ Defence [quoted text clipped - 238 lines] > would not be persuaded even though one came back from the dead to warn them > about hell. See Luke 16:31. > Count your blessings, o ye with decent hearing and cool toys. Which brings up another (old) subject; the mechanism of hearing damage via loud noises (NIPTS), especially why nerve damage damage always starts in the 4k-6k region regardless of the spectrum of the incoming noise. Is it a quantum effect? My first guess a few decades ago was that it was a resonance effect where the ear canal and middle ear were resonant, hence amplified slightly. Later on, another "explanation" appeared; that the hair cells sensing high frequencies are near and just behind the oval window, and hence experiences the most intense noise level. [Also, I now believe that it is the sweeping action resulting from the acoustic velocity of the inner ear liquid within the cochlea that produces the physical damage, and not primarily the acoustic pressure there. This liquid velocity would be greater in certain parts of the cochlear spiral, and less in others especially for mid and low sound frequencies.] Another aspect I have learned is that the damage starts, or is most likely to begin, around 5,600 Hz. Modern hearing testing (not the Bekesey method) simply looks at the discrete frequencies of 3k, 4k, 6k, 8k, and of those, the 4k is the most common indicator (likely because 6k is skipped, and 8k taken instead). But the measured 4k hearing loss is hardly accurate in the sense of mapping primary damage. It is only handy in that everyone makes a 4k measurement, hence it has become the de facto harbinger of NIPTS. So, any good explanation of why primary hearing damage starts in 4k-6k region? Angelo Campanella >> Count your blessings, o ye with decent hearing and cool toys. > [quoted text clipped - 28 lines] > > Angelo Campanella If indeed it really does. There's a critical band that's essential to understanding speech where a little hearing loss does more to affect speech comprehension than other bands. I'd go with explanations supported by solid otology and neurology, myself, if indeed there is such an effect. Peeking online, I see articles on the topic in pubmed.gov (Medical research abstracts), www-nehc.navy.mil (Navy environmental health center), and other reputable sources, as well as a variety of unvetted and other sources. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ >> So, any good explanation of why primary hearing damage starts in 4k-6k >>region? > If indeed it really does. Essentially all the audiograms I have inspected in relation to hearing loss due to occupational noise have that area severely affected (much loss). > There's a critical band that's essential to > understanding speech where a little hearing loss does more to affect > speech comprehension than other bands. In the few kHz region for sure, speech comprehension is severely affected. But my question has to do with the etiology of the dominance of the loss in the 4 kHz area. The 5.6 kHz phenomenon I reference is an area of severe loss, a narrow notch that may be the earliest effect. I venture to say that everyone has a notch there. It might be "antiresonance" in the ear canal, but I have seen no recent elaboration on it. But is it such, or really a sensoneural loss? > Peeking online, I see articles on the topic in > pubmed.gov (Medical research abstracts), www-nehc.navy.mil (Navy > environmental health center), and other reputable sources, as well > as a variety of unvetted and other sources. I think I have seen many of them... I'm just trying to get up-to-date without a lot of effort.... Ang. C. >>> So, any good explanation of why primary hearing damage starts in 4k-6k >>>region? [quoted text clipped - 24 lines] > > Ang. C. I looked at the list of newsgroups you posted to, didn't see sci.med or anything specifically related to otorhinolaryngiology there, would tend to ask active researchers in that field. Here's a link I'd try, just because I've heard of some of these folks's work. http://www.khri.med.umich.edu/ They're making pretty amazing strides in understanding hearing all the way from the ear canal to conciousness and perception, at levels electrical, cellular, mechanical, molecular, genetic... quite a range of stuff. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ > Here's a link I'd try, just because I've heard of some of these folks's > work. > http://www.khri.med.umich.edu/ It looks like they are set up with labs that might make progress in understanding the noise frequency (non) selectivity in causing hearing loss. But that page does not indicate activity in that regard. > They're making pretty amazing strides in understanding hearing all the > way from the ear canal to conciousness and perception, at levels > electrical, cellular, mechanical, molecular, genetic... quite a range > of stuff. That range is apparently what the researchers are interested in, rather than always the problems that need to solved. They must have some well-heeled sponsors.... I should not be so crass.. Thanks for the leads.. Sincerely, Angelo Campanella. >> Here's a link I'd try, just because I've heard of some of these >> folks's work. [quoted text clipped - 19 lines] > > Angelo Campanella. In the event that you and others are interesed in the opinion of one of the top researchers in the field on this matter, you will find it an article by JJ Rosowski which was published in J Acoust Soc Am. 1991 Jul;90(1):124-35. Abstract: A model of external- and middle-ear function is described that uses existing data to quantify the flow of sound power from the environment to the cochlea of humans, cats, and chinchillas. This model estimates the sound power produced at the entrance of the cochlea by an environmental sound stimulus, and can be used to predict the shape of the auditory threshold function and the relative potency of various traumatic acoustic stimuli. The shapes of the predicted and measured threshold functions in the three species are similar in best frequency, bandwidth, and low- frequency slope, and the model accurately predicts the hypersensitivity of the middle-frequency regions of the cochlea to acoustic trauma. The model assumes that the mechanics of the middle-ear system are linear even at high stimulus levels and does not include the effects of either middle-ear or cochlear efferent loops. The effects of these simplifications on the model are discussed as are the implications of the model results for hearing protection and damage > In the event that you and others are interesed in the opinion of one of the > top researchers in the field on this matter, you will find it an article by > JJ Rosowski which was published in J Acoust Soc Am. 1991 Jul;90(1):124-35. That article goes a long way toward establishing the primary parameters needed to model acoustic energy transfer through the outer-middle-inner chain. Very interesting in the parallels between cat, chinchilla and human ears (cats win). The high frequency vulnerability is cited as being around 3 kHz, and attributed to resonance. The same family of resonances has an antiresonance notch around 6 kHz for cats, so the human antiresonance notch may be near 6kHz. > The effects of these simplifications on the model > are discussed as are the implications of the model results for hearing > protection and damage. The tendency to experience hearing damage at frequencies higher than the exciting frequency is also noted, declared to be inconsistent with their existing model, and simply called an anomaly, with no subsequent modeling provided at that time (1991). Nor was any numerical data on these super-frequency anomalies provided. The experimenters that gathered such data published them in a laryngology journal and a 1982 book, making it difficult to study further. My oservations of the very frequent noise damage (NIPTS) that appears early at 4 kHz still stand not yet fully explained. Angelo Campanella snip.....snip > My oservations of the very > frequent noise damage (NIPTS) that appears early at 4 kHz still stand > not yet fully explained. > Angelo Campanella Well, if you put it that way, then there are two separate issues. One has to do with your knowledge. The other has to do with whether or not the noise damage that appears early at 4KHz has been fully explained. As of 8/31/2005, John Rosowski could be contacted via email at <John_Rosowski@meei.harvard.edu>. I assume that he is still at the Mass. Eye and Ear Infirmary and that this email address is still valid. I am confident that he would welcome your inquiry and address any questions/concerns that you may have, and that he would be able to provide you with an up to date assessment regarding the status of research and current thinking on this issue. > As of 8/31/2005, John Rosowski could be contacted via email at > <John_Rosowski@meei.harvard.edu>. I assume that he is still at the Mass. > Eye and Ear Infirmary and that this email address is still valid. I am > confident that he would welcome your inquiry and address any > questions/concerns that you may have, I just sent him a message asking same. Thanks, Ang. C. >> As of 8/31/2005, John Rosowski could be contacted via email at >> <John_Rosowski@meei.harvard.edu>. I assume that he is still at the [quoted text clipped - 6 lines] > Thanks, > Ang. C. I have a further update on this which may be of interest to you. According to my sources, the so-called notch at 4KHz does not mean that maximum initial hearing loss occurs at exactly at 4KHz. For example, maximum initial loss could be at 3.7KHz or 4.3KHz, but that would not be revealed on a standard audiogram because thresholds at 3.7KHz and 4.3KHz are not measured in a standard audiologic test. With regard to the issue of source/cause of the 4KHz notch, there are two very compelling pieces of evidence that locate it peripherally within the cochlea. One piece of evidence is that the so-called 4KHz notch is present in evoked response audiometry, which reflects the strength of frequency- slective synchronous discharges of auditory nerve fibers. The other piece of evidence is that 4KHz notch is associated with abnormal otoacoustic emissions at 4KHz which are believed to be indicative of damage to the cilia of outer hair cells. > Which brings up another (old) subject; the mechanism of hearing > damage via loud noises (NIPTS), especially why nerve damage damage > always starts in the 4k-6k region regardless of the spectrum of the > incoming noise. Because at around 4k the transmission through the outer and middle ear is most efficient, largely due to a quarter wavelength resonance of the ear canal. At those frequencies you simply get more energy to the inner ear to do the damage. In alt.sci.physics.acoustics J Ketutsalo <ei.kiitos@spammia.fi> wrote: > > Which brings up another (old) subject; the mechanism of hearing > > damage via loud noises (NIPTS), especially why nerve damage damage > > always starts in the 4k-6k region regardless of the spectrum of the > > incoming noise. > Because at around 4k the transmission through the outer and middle ear > is most efficient, largely due to a quarter wavelength resonance of the > ear canal. At those frequencies you simply get more energy to the inner > ear to do the damage. You probably know the standard shape of the human audiogram, as shown in http://swfsc.nmfs.noaa.gov/prd/dsweb/tm-256/fig2.gif At -5dB (the average threhold of hearing of a 17yo male at 4kHz) for a passive cochlea, the corresponding vibrations of the fluid in your ear correspond to rms displacement that are less than the mean displacement from Brownian motion. In other words, if it were not for active amplification from outer hair cells, you would not hear anything. The counterpart is that it doesn't take much to mess up your threholds at 4kHz, unlike say at 200Hz where it takes a lot of energy to get any activation in the cochlea. OTOH, your high frequency hearing might be the first to go (we loose about 1Hz/day for the highest frequency we can hear) because all vibrations in the endolymph have to "pass by" the high frequency region of cochlea. So if you hear a very loud, low frequency, sound, it causes large oscillations in the endolymph that have to travel from the base of the cochlea (high-frequency region) to the apex (low-frequency). The shearing effect of this traveling wave might cause damage to the whole cochlea, even the parts that are not tuned to low frequencies. Combine that with high sensitivity to 4-7kHz... Didier SignatureDidier A Depireux ddepi001@umaryland.edu didier@isr.umd.edu 20 Penn Str - S218E http://neurobiology.umaryland.edu/depireux.htm Anatomy and Neurobiology Phone: 410-706-1272 (lab) University of Maryland -1273 (off) Baltimore MD 21201 USA Fax: 1-410-706-2512 > we loose about > 1Hz/day for the highest frequency we can hear) I doubt that very much. N.B. 20,000 / 365 = 54.79, so by your theory by the time you reach 55 years of age your ears' frequency response has decreased from 20 Khz to DC... Bob > In alt.sci.physics.acoustics J Ketutsalo <ei.kiitos@spammia.fi> wrote: >> > [quoted text clipped - 30 lines] > > Didier The implication that loud low-frequency sound creates large motion at the base of the cochlea is misleading and incorrect. At low frequencies (below a few hundred Hz) the pressure at the base of the cochlear does not follow the pressure at the earcrum, but rather decreases with decreasing frequency at an assymtotic rate of -12dB/octave. Furthermore, the motion of the basilar membrane is not determined soly by intracochlear pressure, but by both pressure and stiffness; and the siffness of the basilar membrane decreases exponentially from base to apex. Consequently, because of the relatively low pressure and high stiffness, both the gross motion and the associated micromechnaical motion at the base of the cochlea are no where near as large at low freqeuncies as you imply. According to my calcs if you lose one Hz a day and can hear 20,000 Hz to start you will be about 53 and not be able to hear anything at all. Hmmmmm. TS > In alt.sci.physics.acoustics J Ketutsalo <ei.kiitos@spammia.fi> wrote: >> > [quoted text clipped - 34 lines] > > Didier In alt.sci.physics.acoustics Tom Shaw <tshaw01@comcast.net> wrote: > According to my calcs if you lose one Hz a day and can hear 20,000 Hz to > start you will be about 53 and not be able to hear anything at all. Hmmmmm. Okay, so let me be more precise. You start loosing your upper-frequency of hearing at around 15 years of age (actually, the highest audible frequency for young kids has never been measured reliably. When someone did it on me when I was about 10, my highest audible frequency was around 22500Hz for about 100dB SPL), and as far as I know, your hearing loss slows down around age 50. I mostly had to make the point that you loose your high frequency hearing reliably, whereas the lowest audible frequency does not change that much. Didier SignatureDidier A Depireux ddepi001@umaryland.edu didier@isr.umd.edu 20 Penn Str - S218E http://neurobiology.umaryland.edu/depireux.htm Anatomy and Neurobiology Phone: 410-706-1272 (lab) University of Maryland -1273 (off) Baltimore MD 21201 USA Fax: 1-410-706-2512 I'm sorry. I was just teasing you a little. I am glad to find out that my hearing loss slows down around 50 but it apparently does not stop. I am now at the point where I am bothered by extraneous noise while trying to listen to conversation and that seems to be getting worse. This seems less a problem with frequency response as it is a problem with noise rejection at the mental level. Fortunately I dont notice losing highs any more but probably am. FWIW I bucked rivets in the manufacture of B-24 center-wings when I was eighteen for a few months. That requires you to be inside the wing while the rivet gunner is outside. Sort of like being inside an oil drum with somebody pounding a hammer on the outside. In those days, WWII, nobody worried about ear protection. Today you are not allowed in the airframe factory without ear protection. LOL. In any case my high frequency hearing is shot and that experience was surely part of it's cause. TS PS Skeet shooting isn't such a hot idea for musicians either. > A. Depireux" <didier@umd.edu> wrote in message > news:dpk7em$4gg$1@grapevine.wam.umd.edu... [quoted text clipped - 14 lines] > > Didier In alt.sci.physics.acoustics Tom Shaw <tshaw01@comcast.net> wrote: > I am now > at the point where I am bothered by extraneous noise while trying to listen > to conversation and that seems to be getting worse. This seems less a > problem with frequency response as it is a problem with noise rejection at > the mental level. > Fortunately I dont notice losing highs any more but probably am. Sorry, I don't check news often any more, I don't know of a good service to do it, and the account I am using right now will disappear in a month. With your work experience you probably also get tinnitus? High frequency hearing is important in noisy situations. Think about it: how can you tell the difference between finger snapping in front of you and behind you? In both cases the sound arrives at both ears at the same time. A good part of front-back localization of sounds has to do with the shape of your pinna/ear: the ridges and convolutions are such that some frequencies don't get transmitted that well to your eardrum (there's filtering from your pinna in other words); that filtering is very direction dependent. Hence for a familiar, broad-band sound, localization occurs in part thanks to your ability to identify spectral notches in the perceived sound. Now if you think about the size of your ear and the fact that sound travels at 1ft/s, you will realize that the spectral notches will be in the 8kHz and up region of hearing. In a noisy environment, where you use all the cues you can get, parts of being able to follow a conversation depend on your ability to stream or select the different sound sources that are present and focus your attention on one of those sources. If you have lost your high frequency hearing, the pinna filtering is partially or mostly gone and that's one less cue you can use to isolate a sound source. Noise rejection is not just "mental" as you say, it's also partially physical. Didier SignatureDidier A Depireux ddepi001@umaryland.edu didier@isr.umd.edu 20 Penn Str - S218E http://neurobiology.umaryland.edu/depireux.htm Anatomy and Neurobiology Phone: 410-706-1272 (lab) University of Maryland -1273 (off) Baltimore MD 21201 USA Fax: 1-410-706-2512 Thanks for your comments. I am not bothered by tinnitus. However my noise discrimination is getting worse in that, at first, female voices on TV were often unintelligible but I now notice some of the men's voices are also hard to make out. And, by the way, it is a strong function of enunciation. First rate actors are much easier to make out than a lot of the newbies on the screen. TS > In alt.sci.physics.acoustics Tom Shaw <tshaw01@comcast.net> wrote: >> I am now [quoted text clipped - 40 lines] > > Didier In alt.sci.physics.acoustics Tom Shaw <tshaw01@comcast.net> wrote: > discrimination is getting worse in that, at first, female voices on TV were > often unintelligible but I now notice some of the men's voices are also hard > to make out. And, by the way, it is a strong function of enunciation. > First rate actors are much easier to make out than a lot of the newbies on > the screen. Stop watching TV! Seriously, when you utter a vowel, one of the distinguishing features between the vowels /ah/ and /eh/, for instance, is the location of the "formants", which are spectral peaks in the broad spectrum generated by your vocal chords. For instance, I said "ahhhhhhh" in a mike for 3 second, and took the Fourier transform of the result and put it on http://didier.theearlab.org/ahh.jpg The discrete peaks are the harmonics due to the vibrations of my vocal chords, and the continuous line is supposed to be the spectral envelope (estimated by hand...). The position of the first 2 peaks, at around 500Hz and 1500Hz, varies from vowel to vowel. The other 2 peaks vary a lot less. It's a well known fact that when you enunciate, the peak to trough ratio of formants (in the jpg above, the peak is at 600Hz and the trough at 1000Hz) is maximal. Malcolm Slaney mentioned 15dB is typical. When you speak to people familiar with your voice, esp with your family, it is often down in the 4-5dB range (again, I got this number from Slaney). The other factor to mention in response to your statement is that women have a shorter vocal tract, which means that their formants are about 20% higher in frequency, but their pitch is on average twice as high, which means they have half as many harmonics or discrete lines in the jpg above, which makes it harder to extract vowels from their speech (try to understand a soprano singing an opera!). BTW, it is a studied fact (look up Gordon-Salant on PubMed) that older people have a harder time following fast speech, and it is not a result of their audiogram showing hearing loss. I don't think this phenomenon has been satisfactorily explained, but then again that's definitely nost my field! Didier SignatureDidier A Depireux ddepi001@umaryland.edu didier@isr.umd.edu 20 Penn Str - S218E http://neurobiology.umaryland.edu/depireux.htm Anatomy and Neurobiology Phone: 410-706-1272 (lab) University of Maryland -1273 (off) Baltimore MD 21201 USA Fax: 1-410-706-2512 > In alt.sci.physics.acoustics J Ketutsalo <ei.kiitos@spammia.fi> wrote: >>> Which brings up another (old) subject; the mechanism of hearing [quoted text clipped - 5 lines] >>ear canal. At those frequencies you simply get more energy to the inner >>ear to do the damage. > You probably know the standard shape of the human audiogram, as shown > in http://swfsc.nmfs.noaa.gov/prd/dsweb/tm-256/fig2.gif OK. The resonance explains that at 4 kHz we have the best threshold. I actually enjoyed that for a while in grad school where I used a "Benham Wave Analyzer" (a heterodyning ultrasound receiver) to tune and measure various faint ultrasounds. Mr. Benham was a blind electrical engineer. His instrument used a BFO to create a heterodyne at 4 kHz which was tuned in, then nulled by hand with the aid of a calibrated attenuator. Anyway, I thought it neat then that he used 4 kHz (he being blind and having pristine hearing). > At -5dB (the average threhold of hearing of a 17yo male at 4kHz) for a > passive cochlea, the corresponding vibrations of the fluid in your ear [quoted text clipped - 3 lines] > it doesn't take much to mess up your threholds at 4kHz, unlike say at 200Hz > where it takes a lot of energy to get any activation in the cochlea. OK. Point made. Pristine hearing is also frail in that regard. > OTOH, your high frequency hearing might be the first to go (we loose about > 1Hz/day for the highest frequency we can hear) OK. An oversimplified model of presbycusis... > because all vibrations in the > endolymph have to "pass by" the high frequency region of cochlea. That's dwells on the point I am driving at. The "Cause and Effect" phenomenon here ("Epidemiology?"), according to your expressed model is that it's a happenstance of the location of hair cells. Any hair cell in that high liquid acoustic velocity corridor is going to be zapped. If that is the case, then a bit more publicity and proof-of-prinicipal work and publishing of same is in order, IMHO. > So if you > hear a very loud, low frequency, sound, it causes large oscillations in the > endolymph that have to travel from the base of the cochlea (high-frequency > region) to the apex (low-frequency). The shearing effect of this traveling > wave might cause damage to the whole cochlea, even the parts that are not > tuned to low frequencies. Combine that with high sensitivity to 4-7kHz... OK all of that follows from that model. Some additional parameters, then, presuming that liquid velocity and shear by hair cells is the damage mechanism: 1- It seems clear that the relative motion of the liquid vis a vis hair staffs is vital to hearing; that the Darwin effect (survival of the fittest) will breed organisms whose cochlea promote high velocities from faint sounds. 2- The shell structure of said evolved cochlea will have slightly flexible walls since they will allow extraordinary inner chamber velocities especially when a corridor is formed by a demising wall, i.e. the spiral format. 3- Because the fluid should or must be contained, there will be a "base" where the fluid velocity relative to the walls and surfaces carrying hair cells must of necessity diminish to zero. 4- Because of the conical cross section of the spiral corridor, the greatest relative velocity will occur most of the way from the apex toward the base, perhaps at the 3/4 length location. Whatever hair cells that reside there will experience the first damage when loud sounds as received by the outer ear, and purveyed to the oval window by the middle ear no matter the audio frequency of hat sound. 5- The assignment of specific audio frequencies to hair cells at specific locations remains a mystery. But recent localization tests indicate that precise localization includes the discriminating of time differences in the microsecond range. Sound in water travels .005 feet in one microsecond (1/20th of an inch), so hair cell positional certainty is important to that end. The physiology of the sound path including the stapes bone makes it imperative that asymmetries between left and right ears shall be minimal to nil. A shortened trip to the appropriate hair cells in the cochlear fluid will help. 6- Therefore, the need for precise left-right localization to avoid threats, find food, and hence survive, probably resulted in the high frequency hearing task being assigned by nature (nerve assignment to specific hair cells) to be in the early part of the cochlear corridor for those (high) frequencies vital to precision localization. Angelo Campanella snip....snip > So, any good explanation of why primary hearing damage starts in > 4k-6k region? > Angelo Campanella http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_u ids=1880280&dopt=Citation >>Is there a better theory? I think pretty much all of the physiology of >>hearing is based on this "oft-repeated belief." [quoted text clipped - 3 lines] > being interpreted by the brain, leads to very definite predictions about > how each should behave under experimental conditions. Let's put the question a bit more abstract. Does the spectrum of incoming sound define which nerves are activated (no presure detector, brain working on frequencies much lower than the soundwaves), or does the presure of the sound define which nerves are activated (presure detector, brain works at the frequencies of the sound waves) If you propose the second, is there any proof of any activity in the brain at the required speed level (about 25us or less) SignatureChel van Gennip Visit Serg van Gennip's site http://www.serg.vangennip.com NEW: Recording of Ludwig van Beethoven, Sonata Tempest http://www.serg.vangennip.com/musichigh/N-Beethoven-Storm-20051023.mp3 >>>Is there a better theory? I think pretty much all of the physiology of >>>hearing is based on this "oft-repeated belief." [quoted text clipped - 12 lines] >If you propose the second, is there any proof of any activity in the >brain at the required speed level (about 25us or less) Based on the actual physics and neuroscience I've seen, I wouldn't propose any of the above, and I'd refuse to be constrained to a bifurcation. Last I heard, there are areas of the brain analogous to the spectrum, but not individual sensors analogous to the spectrum. There's an interpretation of periodicity-related information by all the hair cells, and a reinterpretation into spectral data in the brain, and a large range of opportunity for error or illusion in between--which accounts for things like our perceptions of the "fundamental" frequencies of carillon bells, a pitch NOT corresponding with anything in the spectrum. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ >>>>Is there a better theory? I think pretty much all of the physiology of >>>>hearing is based on this "oft-repeated belief." [quoted text clipped - 23 lines] > frequencies of carillon bells, a pitch NOT corresponding with anything > in the spectrum. Well, I think we can be sure the brain is not interpreting signals at a 25us level. So there must be at least one, maybe more mappings from sound patterns before perception. The first mapping has to be at the mechanical level, as the speed of nerve cells is not in the us range. There are some indications that one of the mappings is frequency related: e.g. the sensitivity band of the ear and the changes when people get older, and the existence of "band deafness". It is likely the mapping(s) is (are) more complex. The ear comes early in the evolution. Hearing was not related to music or even communication. I think it was primarely food related: "Is there food or am I food?" Important information that had to be processed fast by primitive brains. SignatureChel van Gennip Visit Serg van Gennip's site http://www.serg.vangennip.com NEW: Recording of Ludwig van Beethoven, Sonata Tempest http://www.serg.vangennip.com/musichigh/N-Beethoven-Storm-20051023.mp3 >It is likely the mapping(s) is (are) more complex. The ear comes early in >the evolution. Hearing was not related to music or even communication. I >think it was primarely food related: "Is there food or am I food?" >Important information that had to be processed fast by primitive brains. Could equally be related to avoiding predation or finding a mate. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ I believe the document I linked earlier explains why taking away one set of receptors does not eliminate a single band of frequencies. It also explains how the model predicts a number of auditory phenomena that have been demonstrated in listening experiments, and which are simple enough for you to try yourself. It has been a few months since I looked at it. I guess my earlier post suggests that "this cell is for G sharp, and this one is for D flat, and so on," but I don't think this is the case. The audible spectrum is sort of "folded" by the structure of the cochlea, and it still requires a brain to turn nerve stimuli into a perception of sound. Missing one or two key points in the math can lead to an assumption that if you took away all the cells in one region, a range of frequencies would be eliminated. IIRC, though, eliminating a few cells would leave a "gap" in the band of stimuli produced by one particular frequency, which the brain would fill in. Some frequencies wouldn't be affected at all. You could only eliminate all perception above a particular frequency, and only by destroying a fairly large region of cells. In such a case it would be difficult to argue which damage resulted in which hearing loss. If you could link us to the studies you're referring to, I'd really be interested in reading them. > > Well, I think we can be sure the brain is not interpreting signals at a > 25us level. So there must be at least one, maybe more mappings from sound > patterns before perception. The first mapping has to be at the mechanical > level, as the speed of nerve cells is not in the us range. I wouldn't call it a mapping, but the transformation of the mechanical movement to neural impulses in the cochlea does this sort of a thing. It is a fact that different frequencies excite the basilar membrane (in cochlea) at different positions. However the tuning is not very sharp, so a single sinusoidal does always cause a range of neurons to fire. The neurons can fire at most about every 1 ms, so the neural data going to the brain is limited to roughly < 1 kHz at the lowest level. > There are some indications that one of the mappings is frequency related: > e.g. the sensitivity band of the ear and the changes when people get > older, and the existence of "band deafness". There are several areas on the pathway from the auditory nerve to the cortex where the sound is being processed. Many but not all are tonotopically mapped (from lower to higher frequencies or the other way around). However, these mappings do not necessarily mean that low frequency neurons are firing less frequently at higher levels in the brain. The mappings can also change somewhat and they have indeed been shown to change due to, for example, hearing damage. What is this conversation doing in the piano and synth groups? > What is this conversation doing in the piano and synth groups? I dunno about the piano group, but sound perception (and anomalies) are very interesting to this synthesist. > > What is this conversation doing in the piano and synth groups? > > I dunno about the piano group, but sound perception (and anomalies) are > very interesting to this synthesist. It was something to do with the statement about 25ths of seconds in the thread "special effects from pianos": http://groups.google.co.uk/group/rec.music.compose/msg/4f965c3c2b89ae5?hl=en "On a normal piano, the maximum repeat rate of an individual note is about ten per second, but If a piano note could be repeated at the rate of about 25 notes per second, the result would be a single continuous tone." Did you know that if you split up a sound into 25ths of a second and then play each 25th of a second backwards consecutively, it sounds the same as the original? (other from any clickiness caused by the joins). It occurred to me that that might from the basis for a DSP data compression algorithm - if you play each 25th of a second forwards and backwards at the same time, the resultant signal is symmetrical, so you only need to store half the signal! Isn't it amazing what clever ears we have - no matter what is fed into them, forwards, backwards inside-out or upside-down, our brains can always make some sense of it! - or is that because we are basically stupid? >> > What is this conversation doing in the piano and synth groups? >> [quoted text clipped - 22 lines] >inside-out or upside-down, our brains can always make some sense of it! > - or is that because we are basically stupid? This is already built into MP3. What's more interesting is that back in the dark ages of computers, a fellow called Iannis Xenakis proposed making entirely new sounds by splicing together segments of roughly this length, and then another much younger fellow (about my age) by the name of Xavier Serra realized that by taking segments this length and overlapping them... or taking similar but overlapping segments of an original sound and reducing the amount of overlap, he could speed up or slow down a sound without changing its pitch. He quickly discovered the use of something called Hamming's Window which eliminated most of the white noise of the splicing clicks. These algorithms were widely published and are built into many DSP systems today, including many you may be familiar with. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ MP3 and Hamming windows compression are mostly related to spectral analysis of sound into its component frequencies and then doing clever mathematical transformations of the results. My simple approach of playing each 25th of a second backwards and forwards at the same time requires hardly any processing, other than the de-clicking. The clicks are quite predictable and easy to understand, so they can quite easily be eliminated - by readjusting the zero at each splice, for example, or selecting a convenient splice point. The clicks aren't white noise, they are caused by the loudspeaker cone attempting to move or change direction too quickly for its design specifications - some digitally-generated clicks are actually miniature 'sonic booms' caused by the loudspeaker diaphragm moving faster than the speed of sound! (If the the maximum distance that it can move is 1/4", if consecutive samples are the max and min values, at 40KHz sampling rate the speed is 10,000"/sec). What the original "how your ears work" ( http://ultrapiano.com/manufacturers/EarPage.jpg ) is getting at is that the ear and brain do not perform spectral analysis of sound at all! What instead happens is that patterns of pressure variations are recognised while they are on the aural nerve. From this simple information we recognise human speech and can distinguish between words and understand its emotional content. Musicians can train their ears to hear spectral components in a musical sound, but many natural sounds are very complicated things consisting mostly of transients, with hardly any meaningful frequency information. Even the loudness of a sound depends entirely on its context - a soft noise can sound remarkably loud in the context of silence, and MP3 compression makes use of this - it's similar to the old Dolby system on analogue recordings that reduces background hiss during quiet passages. > >> > What is this conversation doing in the piano and synth groups? > >> [quoted text clipped - 41 lines] > To be great, do better and better. Don't wait for talent: no such thing. > Brights have a naturalistic world-view. http://www.the-brights.net/ >MP3 and Hamming windows compression are mostly related to spectral >analysis of sound into its component frequencies and then doing clever [quoted text clipped - 26 lines] >use of this - it's similar to the old Dolby system on analogue >recordings that reduces background hiss during quiet passages. A splice at a nonzero point in a waveform is white noise. It literally has every frequency component in it. As does a single-sample spike in the middle of silence. This comes directly from the sampling theorem. Yes, adjusting the edit point to the nearest zero-crossing will help to eliminate noise. So will a Hamming window. Each takes a certain amount of computing power, linear in the number of times it is applied. Try 'em both and see which one sounds best to you. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ Transients are where it's at, frequency-wise. Have you ever looked at a spectrogram of a sound audible to humans, and wondered why the majority of the graph is dedicated to pitches above 1 kHz? Practically all of the information that identifies a sound is near the top of our audible spectrum, and it's the "kinks" in signals that carry this high-frequency content. If you chop up a sound into 1/25-sec pieces, and throw half of them away, you won't lose any information at all, unless the original sound has a fundamental frequency of less than 25 Hz. For most of us, that is too low a frequency to hear, so few sounds of interest to us fit into this category. Any high-frequency components that are present in the first half of each "chunk" will also be present in the second half, so it makes sense that you won't lose the "intelligence" of the signal by doing this. And the savings of 50% is trivial if you compare it to existing techniques that are less lossy and less proccessor-intensive. Assuming that your chopping technique is perfect, and you eliminate any transients due to the ends not matching up, you may not be able to hear a difference, but this is not because it takes your brain 1/25 of a second to identify a change in spectrum. It's because if you did everything right, the spectrum never changed. The whole point of Hamming and other sampling windows is to make it possible to chop up signals into pieces and preserve their spectral content. It just puts the distortion into phase changes or areas of the spectrum outside the region of interest (which is usually outside our range of hearing when it's audio signal processing). Consider the difference in spectral content between 9 Beet Stretch and Beethoven's 9th. > Musicians can train their ears > to hear spectral components in a musical sound, but many natural sounds > are very complicated things consisting mostly of transients, with > hardly any meaningful frequency information. I'd be interested in how well this reversing 1/25s of a second works for high unreverberated xylophone notes. I choose those because almost-periodicity sets in almost immediately after the bars are struck, and the amplitude tends to decay to inaudble within a single cycle--which indicates just how sensitive our frequency-extrapolating mechanism is, but it also means you may have much less than 1sec/25 to work with. SignatureMatthew H. Fields http://www.umich.edu/~fields Music: Splendor in Sound To be great, do better and better. Don't wait for talent: no such thing. Brights have a naturalistic world-view. http://www.the-brights.net/ Here's a short program you can use to test .wav files (It's untidy and badly written but it works! - the first chunk handles the .wav formatting information and then it just reverses every 25th of a second of the input file and puts it in the output file. > I'd be interested in how well this reversing 1/25s of a second works > for high unreverberated xylophone notes. I choose those because [quoted text clipped - 8 lines] > To be great, do better and better. Don't wait for talent: no such thing. > Brights have a naturalistic world-view. http://www.the-brights.net/ #include <io.h> #include <stdio.h> /* main algorithm opens INfile reads 25ths of seconds forwards, writes backwards to OUTfile */ #define BUFFSIZE 1764 /* 25th of a second at the sampling rate of INFile */ FILE *OUTfile, *INfile; char ChunkID[4]; long LongInt; short int ShortInt; short int n, buffer[BUFFSIZE], bcount; int main(int argc, char **argv) { if((INfile = fopen("C:\\sound\\wavs\\INmail.wav","rb"))==NULL) { printf("failed to open file C:\\sound\\wavs\\INmail\n"); } else printf("Input file C:\\sound\\wavs\\INmail.wav opened OK\n"); if((OUTfile = fopen("C:\\sound\\wavs\\OUTmail.wav","wb"))==NULL) { printf("failed to open file C:\\sound\\wavs\\OUTmail.wav\n"); } else printf("Output file C:\\sound\\wavs\\OUTmail.wav opened OK\n"); n = fread(ChunkID, 4, 1, INfile); /* "RIFF" */ printf(" %c %c %c %c \n", ChunkID[0],ChunkID[1],ChunkID[2],ChunkID[3]); fwrite(ChunkID, 4, 1, OUTfile); n = fread(&LongInt, 4, 1, INfile); /* Total INfile size (-4) */ printf("Chunksize is %d\n", LongInt); fwrite(&LongInt, 4, 1, OUTfile); n = fread(ChunkID, 4, 1, INfile); /* "WAVE" */ printf(" %c %c %c %c \n", ChunkID[0],ChunkID[1],ChunkID[2],ChunkID[3]); fwrite(ChunkID, 4, 1, OUTfile); n = fread(ChunkID, 4, 1, INfile); /* "fmt " */ printf(" %c %c %c %c \n", ChunkID[0],ChunkID[1],ChunkID[2],ChunkID[3]); fwrite(ChunkID, 4, 1, OUTfile); n = fread(&LongInt, 4, 1, INfile); /* 16 */ printf("SubChunk1Size is %d\n", LongInt); fwrite(&LongInt, 4, 1, OUTfile); n = fread(&ShortInt, 2, 1, INfile); /* 1 */ prin |
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