[Top] [All Lists]

Re: Questions for audio gurus

Subject: Re: Questions for audio gurus
From: "Julius Thyssen" <>
Date: Thu, 23 Feb 2006 00:06:34 -0000
Dan Seven <> wrote:

> A quick question or 2 ..If a recorder is capable
> of a frequency range of 20 to 20kHz such as a new
> Tascam HD P2 and it can utilize192 kHz sampling
> frequency, can you actually hear the upper end
> of the audible range better?

As the Whittaker=96Nyquist=96Kotelnikov=96Shannon sampling theorem states;
When sampling a band-limited signal (e.g., converting from an
analogue signal to digital), the sampling frequency must be
greater than twice the input signal bandwidth in order to be able
to reconstruct the original perfectly from the sampled version.

The thing really important is the low-pass filtering
that takes place when you sample audio. If you sample
with 192 kHz, you'll be including sound up to 96 kHz.

Say you have a microphone that picks up audio up to 18 kHz
(and is REALLY not picking up ANY audio higher than 20 kHz).
If you would sample that microphone output using a 44.1 kHz
sample frequency, you will need to be sure that the band-pass
filter works perfectly within 44.1 / 2 =3D 22.05 - 20 kHz =3D 2050 Hz.
Most modern day analogue low pass filters on 16 bit samplers are
almost perfect when they can use a transition band of 2000 Hz.
So the 2050 Hz needed in this example is good enough.
In this case you will not need a higher samplerate than 44.1 kHz.
Some cheaper low-pass filters still touch lower frequencies
more than they should. This is why people use oversampling,
like with the use of 88.2 or 96 kHz. It is *only* required
if the low-pass filters (used for the transition band of the
needed anti-aliasing) are doing necessary work, because the
audio that is being picked up has a higher freq. range
than that which is sampled. This is only rarely the case.

Personally I would never have signed the OK for Red Book
CDDA (audio CD) standard. 22050 Hz is simply too close
to the edge of our hearing range (asking for trouble
and wasting the world's time with an imperfect format).
48 kHz samplerate would be a very good safe choice for
most analogue recording and pick-up equipment out there.

And to think people used to record from FM-stereo radio
to cassette and were happy with the quality. ;-)
We're talking *already* low-passed audio at 15 kHz.
To equal that range, a sample rate of 32 kHz is sufficient.
For some strange reason absurd frequencies have been made
into a standard for DVD-audio. I think it's much more
"because we can" than "because we need it".

The thing causing this increase is that new equipment (and its
analogue to digital converters and digital to analogue converters)
has gotten better, resolution-wise. 24 bit is no problem anymore.
That this would require a bigger frequency range for anti-aliasing,
is, strange enough NOT true: The more can be done in the
digital domain, the more perfect anti-aliasing will be.
So the question is: How good is the anti-aliasing filter
in your Tascam recorder ?

There have been too many listening tests that proof beyond
any doubt that humans do NOT hear the difference between
originals and their 48 kHz or 96 kHz sampled recordings,
simply because we can not feel or hear frequencies higher
than 22 kHz, and the source of the sampled audio is rarely
producing higher frequencies than 22 kHz at all. Plus, if
it's only there to cause harmonics and timbre related
influences, one could question its value; Most anti-
aliasing artifacts are harmonically fine, they might
cause a different sound than the original, but what
will be left after masking by other louder parts
in the spectrum is hardly measurable anyway.

There's interesting reading (although already somewhat expired)
on this subject here:


<Prev in Thread] Current Thread [Next in Thread>

The University of NSW School of Computer and Engineering takes no responsibility for the contents of this archive. It is purely a compilation of material sent by many people to the naturerecordists mailing list. It has not been checked for accuracy nor its content verified in any way. If you wish to get material removed from the archive or have other queries about the archive e-mail Andrew Taylor at this address: andrewt@cse.unsw.EDU.AU