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Natural Science Forum / Physics / Acoustics / August 2006standard for earbud THD+N?
Newbe here What is the iPod or defacto standard for earbud acoustic THD+N. Seems like 1% -5% is the target But I'm looking for what do most people want Vs what they get in a typical consumer portable audio player?You know benchmark testing. When is a new audio player product quality competitive with the standard . Any papers, tech websites etc? Thanks Kevin T > Newbe here > [quoted text clipped - 7 lines] > Thanks > Kevin T On what basis do you believe that there is a "defacto" standard for earbud acoustic THD? Also, because earbuds are passive devices, acoustic N=0. Sorry Let me try again. For the sake of this question I make a leap of faith assumption based on sales that Apple has the defacto personal audio player (iPod) and it sets a benchmark for audio performance in that class.. OK . When is a new consumer portable audio player products acoustic quality competitive with a typical iPod? What are the in ear performance metrics for the player/earbud system? Is THD of 5% -10% typical for cheap included earbuds? If frequency / impulse responce amplitude and phase liniarity are good at the same SPL what makes a player "iPod" sound quality? What make one sub par? Thanks Kevin T What is the iPod or defacto standard for earbud acoustic THD+N. Seems > > like 1% -5% is the target But I'm looking for what do most people want > > Vs what they get in a typical consumer portable audio player?You know > > benchmark testing. When is a new audio player product quality > > competitive with the standard . > > Any papers, tech websites etc? > > Newbe here > > [quoted text clipped - 3 lines] > On what basis do you believe that there is a "defacto" standard for earbud > acoustic THD? Also, because earbuds are passive devices, acoustic N=0. > Sorry > [quoted text clipped - 12 lines] > Thanks > Kevin T I think one has to view the iPod as a total system. That system includes the MP3 decoder, the DAC, the earbuds, the download system, marketing, coolness factor, price point, etc. I have a feeling sound quality is only a small part of what's driving that market. How large is the earbud upgrade market? If earbud quality were a major issue I'd expect a large upgrade market to evolve. One might view the iPod was a disruptive technology of the "walkman" world. I think it will take more than earbuds to disrupt the iPod world. Later... Ron Capik -- > Sorry > > Let me try again. For the sake of this question I make a leap of faith > assumption based on sales that Apple has the defacto personal audio > player (iPod) and it sets a benchmark for audio performance in that > class.. OK . In that class, it may well be a "benchmark," but MP3 quality audio is poor at best. Furthermore, the "iPod" is a aimed at a mass market where audio quality is not at the top of the priority list. So your question really is when is one poor quality system judged to be superior to another poor quality system. > When is a new consumer portable audio player products acoustic quality > competitive with a typical iPod? When a sufficient number of reviewers and users of such equipment reach a consensus. > What are the in ear performance metrics for the player/earbud system? Whatever the manufacturer's choose to specify. > Is THD of 5% -10% typical for cheap included earbuds? THD depends on frequency and level. Consequently there is no simple or general answer to that question. Cheap earbuds, like cheap headphones, are evaluated subjectively, not quantitatively. There are several high quality earbuds (see www.headwise.com), but the cheap earbuds supplied with the "iPod" are not among them. > If frequency / impulse responce amplitude and phase liniarity are good > at the same SPL what makes a player "iPod" sound quality? What make > one sub par? > > Thanks > Kevin T On what basis to you believe that the "iPod" system with supplied cheap earbud has good frequency response, impulse response and phase linearity? > Is THD of 5% -10% typical for cheap included earbuds? I would think that 5% and up is "poor" quality for music, especially designer music for which most persons use Ipods. Speech can tolerate 10%, but not music. If Ipods want to be premier, they should strive for 1% to 3% as maximum. Since High volume level has been the rule of the market, the manufacturers should easily be capable producing litening devices of that low distortion level for all normal (intelligible) listening. They might let 10% ofccur at full volume, and such distortion can encourage folks to NOT listen to such a high level since it is "muddy". > If frequency / impulse responce amplitude and phase liniarity are good > at the same SPL what makes a player "iPod" sound quality? What make one > sub par? Either muddines, or buds that won't stay in the ear (my complaint). I don't have an Ipod, but I do have tape recorders that come with earbuds. Angelo Campanella > > Is THD of 5% -10% typical for cheap included earbuds? > [quoted text clipped - 17 lines] > > Angelo Campanella I really appreciate this discussion and maybe there is no good answer:( I understand I am looking at only part of the product the consumer will use but I need to answer the HW questions before I'll ever hope to quantify the pandoras box of H/W plus lossy codec issues. For reasons of clarity need for early data I want to isolate /quantify audio H/W performance of a new player with lossless.wav file from any & all lossy coder issues. :( Here is my issue and my question. Let's say this new audio player design's for the same market as iPods (Apple does'nt publish audio specs). What level / metric of lossless audio quality must I meet to be as good as current iPod ( system w/ supplied earbuds) . If I meet these I can use the many stand-alone codec quality tools and then finally subjective evaluations of the complete codecs+player HW system to assure conpetitiveness. Thanks Kevin T Thanks Kevin, > What level / metric of lossless audio quality must I meet < I don't see why the quality of an MP3 player would be assessed any differently than any other piece of gear. So there's frequency response, distortion, noise, and time-based errors. That's about it! --Ethan > Kevin, > [quoted text clipped - 5 lines] > > --Ethan Has any recognized lab done that on iPods? KT >>I don't see why the quality of an MP3 player would be assessed any >>differently than any other piece of gear. So there's frequency response, >>distortion, noise, and time-based errors. That's about it! > Has any recognized lab done that on iPods? I have no idea why a US lab would do that for a foreign product other than to inform same to a US producer.. As far as the measrurement is concerned, a good approximate answer can be obtained with a common sound level meter with a 1/3-octave band (or even an octave band) analyzer: Run a est tone signal into the earbud. Set SLM mic near the earbud as if it (the SLM mic diaphragm) were an eardrum. Take a full frequency spectrum of the sound from the earbud. Note the dB levels of all the bands received by the SLM analyzer. E.g. fo a 500 Hz tone: expected harmonic signals: signal 1/3 band symbol here 1k 1k L2 1500 1.6k L3 2k 2k L4 2.5k 2.5k L5 3k 3.1k L6 3.5k ?split between 3.1k and 4k L7 4k 4k L8 4.5 etc; you can figure that out. L9 The metric recorded is sound level in decibels re 20 micropascals. The energy in the harmonics is the sum of all the stuff not in the fundamental. You calculate the distortion energy, D, conveniently in dB for instance D = 10*LOG(10^(L2/10) + 10^(L3/10) + 10^(L4/10) +......) Thus, for instance if the 500 Hz band fundamental tone level was 90 dB, then the 1k band my regiser 72 dB, the 1600 band may register 55 db, the 200 band may register 45 dB, the 2500 band may register 30 dB, etc. The 1/3 octave bands in between, 630, 800, 1250, etc, will be at the noise floor of your SLM and may not be of concern (unless the speaker (bud) is scratchy). So maybe the D decibel sum becomes, say 73 dB. That's a 17 dB drop from 90. 17 dB represents 1/50th: 10^(17/10)=50 1/50 = .02 = 2% Other tone frequencos can be used, and one should do a fewand average... I hope this helps. Angelo Campanella >>>I don't see why the quality of an MP3 player would be assessed any >>>differently than any other piece of gear. So there's frequency response, [quoted text clipped - 14 lines] > > E.g. fo a 500 Hz tone: irrelevant details snipped > Angelo Campanella The response that an earphone or headphone produces at the eardrum depends on the acoustic output impedance of the earphone or headphone, the acoustic characteristics of the coupling/path (pinna and concha) and the acoustic impedance of the load (acoustic impedance at the plane of the entrance of the ear canal). Aside from real ear measurements, the proper way to estimate with reasonable accuracy the response of and distortion produced by a earphone, headphone or insert earphone (either full insert or partial insert such as the "earbud") is on an ear simulator such as the B&K HATS and the Knowles KEMAR. >>>>I don't see why the quality of an MP3 player would be assessed any >>>>differently than any other piece of gear. So there's frequency [quoted text clipped - 15 lines] >> >> E.g. fo a 500 Hz tone: To be honest Angelo, I'm not really sure what a 1/3 octave spectrum analyser would tell you about 'hifi'. Perfectly good speakers, such as my ancient B&Ws, have a 1/3 octave response that is all over the place. Your ear adjusts. > The response that an earphone or headphone produces at the eardrum > depends on the acoustic output impedance of the earphone or headphone, [quoted text clipped - 8 lines] > HATS and the Knowles KEMAR. > Ghost, could you perhaps use reciprocity and a pair of buds in a very short, stiff tube? I've never done it, but I have seen calibrators for intensity mic pairs that use this technique, I think. Cheers Greg Locock > To be honest Angelo, I'm not really sure what a 1/3 octave spectrum > analyser would tell you about 'hifi'. Perfectly good speakers, such as > my ancient B&Ws, have a 1/3 octave response that is all over the place. > Your ear adjusts. An original question was 'how to Measure harmonic distortion?' My answer is -using 'standard' acoustical hardware, one could do it as I specified. The 1/3 octave filters offer a convenient (to me) way to pick up the harmonic energy separately from the fundamental energy in the sound emerging from the speaker ('bud' in this case). A far as 'frequency response' is concerned - true - the 1/3 octave display of the response' from a speaker is more often than not 'all over the place', but that's reality. The reasons why this is common is interrelated with economics, the reality of sound production and the accommodations furnished by our brain hearing processing. Things 'are what they are': The speech and music signal processing furnished by our brain compensates for a lot of irregularity in frequency and phase response. Sales literature abhors wiggly lines; it reduces their universe to flat lines and monotonic curves (no wiggles) by various smoothing conventions and/or blarney. Some only publish their system's electrical response driving a fixed resistor load. The speaker is left to 'others' to detail. The audiophile public remains gullible to such smoothing because they want to believe it. Very attractive (visually) enclosures, knobs and names assist in digesting the blarney, accepting it all as 'delicious'. My audio systems will immediately be interned on the common junk pile once they leave my home. The largest was built by me into a long functioning storage cabinet in the 1960's, containing 16 small speakers of questionable frequency response, a pair of tweeter speakers and some Eq. I have them tweaked in favor of speech intelligibility. I love to listen to talk radio and to symphonic classical music. As background, this is good enough for me. If it sounds good, it IS good. Angelo Campanella Angelo, > Sales literature abhors wiggly lines < No kidding. Audiophiles, and even many pros who should know better, obsess over minutiae like jitter that's 120 dB below the music, and having a frequency response flat to 100 KHz, all the while ignoring 30 dB or more variations in the low frequency response of their rooms. --Ethan >> To be honest Angelo, I'm not really sure what a 1/3 octave spectrum >> analyser would tell you about 'hifi'. Perfectly good speakers, such as [quoted text clipped - 5 lines] > My answer is -using 'standard' acoustical hardware, one could do it as I > specified. snip....snip > Angelo Campanella The measurement method you proposed is valid only in a situation where system resonances and antiresonances are not involved, such as in a free field measurement situation. If you are measuring in a room the distortion of a loudspeaker, excited by a 100Hz signal, and if your measurement microphone is located in a room resonance (antiresonance) at 300Hz, the level of the third harmonic will be amplified (attenuated) at that measurement location. Similarly, the distortion at the eardrum produced by an earbud will depend on the system resonances, which include, but are not limited to the resonances of the concha and ear canal. snip...snip > Ghost, could you perhaps use reciprocity and a pair of buds in a very > short, stiff tube? [quoted text clipped - 4 lines] > Cheers > Greg Locock Reciprocity calibration of microphones is used to determine absolute sensitivity, which is not applicable in this situation because the issue is frequency response, not absolute sensitivity. The three factors affecting frequency response are 1) blocked pressure (pressure into an infinite impedance acoustic load), 2) acoustic impedance of the source, and 3) acoustic impedance of the load. Since (1) and (2) are both unknown (and difficult to measure), and since (3) is known, the most expedient method of measuring the frequency response of an arbitrary transducer into a known acoustic load is to place the transducer on a device that simulates the known acoustic load. This is exactly the same method that is used to "calibrate" headphones for audiomety except that the determination of sound pessure at the eardrum that is produced by audiometric headphones is only obtained at discrete frequencies rather than as a continuous frequency response function. > Has any recognized lab done that on iPods? > > KT I don't know about "recognized" labs, but you can read two detailed sets of electrical measurements at <http://home.comcast.net./~machrone/playertest/playertest.htm> and <http://www.stereophile.com/mediaservers/934/index5.html> I don't know of anyone that has done SPL measurements through the included earbuds. By all informal subjective accounts the earbuds are crap. I never even opened the earbud package that came with my nano, but I was lucky enough to get a free pair of Etymotic ER-6's. >>Has any recognized lab done that on iPods? >> [quoted text clipped - 4 lines] > > <http://home.comcast.net./~machrone/playertest/playertest.htm> That one has nothing to do with THD. It shows square waves, which are best at evluating low frequency roll-off (droop means it passes little low frequency audio below the rep rate of the square wave). The high frequency limit is harder to see, being essentially the reciprocal of the rise time of the square wave edges. > and > > <http://www.stereophile.com/mediaservers/934/index5.html> Only one of those graphs has anythig to do with THD... The graph labeled "1kHz dithered". There you see a little spur at 2 kHz 16 dB down from the 1kHz tone.. 16 dB = 2.5% THD. > I don't know of anyone that has done SPL measurements through the > included earbuds. wh do anything else? > By all informal subjective accounts the earbuds are > crap. I never even opened the earbud package that came with my nano, but > I was lucky enough to get a free pair of Etymotic ER-6's. Crap for music, but OK for field checking for a few seconds to determine whether system is working. Angelo Campanella > >>Has any recognized lab done that on iPods? > >> [quoted text clipped - 35 lines] > > Angelo Campanella And required if you're doing an "apples to apples" fair comarision of "included in box headphones " from one player system to another. This is what the consumer hears before they start mix/matching things I can't control. Kevin T |
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