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Natural Science Forum / Physics / Acoustics / January 2008



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Definition of "Frequency Content"

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mwaelt@gmail.com - 24 Jan 2008 11:17 GMT
Dear all,

I am looking for a precise definition of the term "frequency content".
Can anybody help or point me to specific literature?

Thanks a lot!
Don Pearce - 24 Jan 2008 11:22 GMT
>Dear all,
>
>I am looking for a precise definition of the term "frequency content".
>Can anybody help or point me to specific literature?
>
>Thanks a lot!

I don't believe it is a term with a precise definition. Since any real
signal contains noise, which by definition contains all frequencies,
then you could say that the term is thus rendered meaningless. You
need to understand exactly what you mean when you say it, and make
sure your reader does as well.

d

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Steve - 25 Jan 2008 05:28 GMT
> On Thu, 24 Jan 2008 03:17:56 -0800 (PST), "mwa...@gmail.com"
>
[quoted text clipped - 16 lines]
> --
> Pearce Consultinghttp://www.pearce.uk.com

Agreed that "frequency content" is an imprecise term.  What it usually
means is the frequency range of your signal of interest.  Let's say
your microphone measures signal energy throughout the nominal audible
range of 20-20000 Hz.  If you are interested in measuring the Taos Hum
(see Wikipedia) then the signal of interest has a "frequency content"
of perhaps 20-70 Hz even though your transducer is picking up all
sorts of other ambient noise.  If you are interested in telephone
audio signals then your frequency content is something like 300-3000
Hz.

Steve
mwaelt@gmail.com - 25 Jan 2008 15:35 GMT
> > On Thu, 24 Jan 2008 03:17:56 -0800 (PST), "mwa...@gmail.com"
>
[quoted text clipped - 28 lines]
>
> Steve

Hi all,

thanks for your quick replies. So, as I understand it now, "frequency
content" is the range of 'significant' spectral energy. But without
considering the spectral "shape"? I.e., the actual energy distribution
is not inherently covered by the term "frequency content"? Or is it a
matter of definition?

Thanks again
Don Pearce - 25 Jan 2008 15:41 GMT
>> > On Thu, 24 Jan 2008 03:17:56 -0800 (PST), "mwa...@gmail.com"
>>
[quoted text clipped - 38 lines]
>
>Thanks again

If you are producing sounds, "frequency content" may be those
frequencies you consider significant to the purpose. But you may want
to broaden the definition to include those that are there in
significant quantity, even if they are unwanted.

As I said, this is not a term with a precise definition within the
art. It will mean what you want it to mean. Just be clear about what
you are saying.

d

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http://www.pearce.uk.com

Angelo Campanella - 27 Jan 2008 01:35 GMT
>>>>On Thu, 24 Jan 2008 03:17:56 -0800 (PST), "mwa...@gmail.com"
>>>>>I am looking for a precise definition of the term "frequency content".
>>>>>Can anybody help or point me to specific literature?

    The term 'frequency content' (of a sound or signal) is typical "jargon"
(lazy English?) comprising a one-dimensional description of
two-dimensional phenomenon.

    The quantities alluded to are the material content of the sound or
signal in terms of all the frequency components, the frequency range
over which they occur, and the sound energy of each component. The
parsing of the sound or signal energy into individual components is up
to the scruples producer of the quantity (let's call it a "spectrum" for
brevity).

    Angelo Campanella
Steve - 28 Jan 2008 03:57 GMT
On Jan 25, 10:35 am, "mwa...@gmail.com" <mwa...@gmail.com> wrote:

> > > On Thu, 24 Jan 2008 03:17:56 -0800 (PST), "mwa...@gmail.com"
>
[quoted text clipped - 40 lines]
>
> - Show quoted text -

It occurred to me that we're replying based on our assumptions of what
you want to talk about in terms of frequency content.  It would be
helpful if you would describe your project a little and who is the
intended audience for your presentation.  Or maybe it's not a project
for someone at all?  Anyway, the more background information the
better.

In short, a Fourier frequency analysis of a signal will give you a lot
of information, if you know what you want to look for. But it won't
give you everything.  Depending on the type of signal and whether you
are looking for evidence of physical processes or perhaps perceptual
attributes, you may have everything you need or may need to look into
further signal analysis.  Sorry if I have muddied the waters.  As an
acoustical consultant once told me (only half-jokingly?), one
necessary conclusion of every funded study is that it needs futher
(funded) study.

Steve
 
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