Wave-to-Wave Recording. Noisy on Low Volume!

Why is it whenever I record from one wave file - at an extremely low
volume - another wave file, I get noise?

The process is completely digital. There is no analog, no D-A, and no
A-D. Why the #%!$@%!@# is their noise?

Since this is not analog-to-digital, this is obviously *not*
quantization noise. Quantization noise only occur during A-D
conversion when the input volume and/or bit-resolution is inadequate.

Curious wrote:

> Why is it whenever I record from one wave file - at an extremely low
> volume - another wave file, I get noise?
> 
> The process is completely digital. There is no analog, no D-A, and no
> A-D. Why the #%!$@%!@# is their noise?
> 
> Since this is not analog-to-digital, this is obviously *not*
> quantization noise. Quantization noise only occur during A-D
> conversion when the input volume and/or bit-resolution is inadequate.

The devil is probably in the details.  Describe more precisely what
you are doing.

-- 
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam.  Our true address is of the form che...@prodigy.net.

curious11112001@yahoo.com (Curious) writes:
>Why is it whenever I record from one wave file - at an extremely low
>volume - another wave file, I get noise?

>The process is completely digital. There is no analog, no D-A, and no
>A-D. Why the #%!$@%!@# is their noise?

>Since this is not analog-to-digital, this is obviously *not*
>quantization noise. Quantization noise only occur during A-D
>conversion when the input volume and/or bit-resolution is inadequate.

My guess, and it is just a guess, because I can't see into the
contents of the files you have before or after the copy, is this
is the audible result of the wild proliferation of different
streams of bytes that all get lumped into the name "wave file."

Take a peek at
http://www.borg.com/~jglatt/tech/wave.htm
for just a hint at some of what has been done with this.

If you dig around you might be able to find a utility that will
show you all the gory details of the contents of your wave file,
the original and the copy you make, and see what was done to the
contents to just make that copy.  I had a utility for this but I
can't find it here now.

curious11112001@yahoo.com (Curious) writes:
> [...]
> Since this is not analog-to-digital, this is obviously *not*
> quantization noise. Quantization noise only occur during A-D
> conversion when the input volume and/or bit-resolution is inadequate.

Wrong. Quantization can occur digitally as well. In fact this type
of quantization is routinely performed these days in mastering CDs
since many professional mixes are at 24 bits (or higher) and have
to be converted to 16 bits for CD. 

When you gain the volume down, you are essentially requantizing. You're
taking something that once occupied X dB of dynamic range and reducing
it by Y dB (of gain). The fact that you aren't throwing away the unused
bits that result is irrelevent - you have requantized.

You must be gaining down significantly in order for noise to be a problem.
What are you doing? Or was this just an experiment/curiosity?
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curious11112001@yahoo.com (Curious) wrote in message news:<34a4f456.0403262326.a24d249@posting.google.com>...
> Why is it whenever I record from one wave file - at an extremely low
> volume - another wave file, I get noise?

What do you mean by "record?"

> The process is completely digital. There is no analog, no D-A, and no
> A-D. Why the #%!$@%!@# is their noise?
> 
> Since this is not analog-to-digital, this is obviously *not*
> quantization noise. Quantization noise only occur during A-D
> conversion when the input volume and/or bit-resolution is inadequate.

Wrong. Quantization noise will occur EVERY TIME truncation takes
place. If you take an 18 bit sample stream and throw away the
bottom two bits, even though the process is "completely digital,"
with "no analog, no D-A and no A-D," you will, absolutely positively
get the #%!$@%!@# quantization artifacts.

Now, you say you are getting "noise." What do you mean by "noise?"
Is it random hiss, or is it a grungy, signal-dependent noise? If
it's the former, it could be the application of flat dither to
eliminate the quantization artifacts. If it's the latter, it 
probably IS quantization artifact.

But, as mentioned elsewhere, the devil IS in the details. What do
you mean "record?" What are you trying to do using what process
or software? What does the "noise" sound like? Without those details,
definitive, helpful answers are impossible.

curious11112001@yahoo.com (Curious) wrote in message news:<34a4f456.0403262326.a24d249@posting.google.com>...
> Why is it whenever I record from one wave file - at an extremely low
> volume - another wave file, I get noise?
> 
> The process is completely digital. There is no analog, no D-A, and no
> A-D. Why the #%!$@%!@# is their noise?
> 
> Since this is not analog-to-digital, this is obviously *not*
> quantization noise. Quantization noise only occur during A-D
> conversion when the input volume and/or bit-resolution is inadequate.

Actually, quantisation noise is added as soon as anything but pure
copying or shifting is done in the digital domain. No A/D conversion
is needed for this to occur. So, filtering, gain adjustment, up/down
sampling etc adds noise since they usually yield more bits than the
original signal, and these extra bits have to be truncated to fit in
the same format. Also, if everything is to be done perfectly, dither
noise should be added at each such truncation.

On 26 Mar 2004 23:26:23 -0800, curious11112001@yahoo.com (Curious)
wrote:

>Why is it whenever I record from one wave file - at an extremely low
>volume - another wave file, I get noise?
>
>The process is completely digital. There is no analog, no D-A, and no
>A-D. Why the #%!$@%!@# is their noise?
>
>Since this is not analog-to-digital, this is obviously *not*
>quantization noise. Quantization noise only occur during A-D
>conversion when the input volume and/or bit-resolution is inadequate.


Well. if you're reducing the volume then you are throwing out usable
snr.  Please describe how you are doing this re-recording?  If this is
windows and you're playing the file and using a recorder, then you are
actually doing a/d -> d/a.  Also check that you don't have other
sources enables such as the line-in or mic inputs which will
contribute.

-Chris

chris@nospam.com wrote in message news:<iace60hkrbgkdfo2fvcmaqvdbuav91b7c8@4ax.com>...
> Please describe how you are doing this re-recording? 

Play wave file in Realone player and record using Wavelab at approx.
the same time. First click record in Wavelab and then click play on
Realone.

> If this is
> windows and you're playing the file and using a recorder, then you are
> actually doing a/d -> d/a.  

It all occurs within the computer itself. No cables needed. The only
thing "analog" is the end product, that is the signal the human ear
can perceive. Before the d-a, the information is purely digital.

It is poor a-d (not d-a) conversion that results in quantization
noise. An analog signal too soft will have its values improperly
rounded. This will cause quantization noise.

I think - but don't know - that the noise I'm getting is due to random
amplification of any expected digital signal. This is a lot like a PCM
radio receiver "trying its best" to catch and amplify a signal in an
area:

1. With extremely poor reception 

AND

2. Pervaded with EMI, RFI, magnetic, and other inteferences

The PCM receiver expects a digital signal and not an analog one. Any
surrounding "PCM-like" radio waves at the receiver's frequency will
cause disruption.

> Also check that you don't have other
> sources enables such as the line-in or mic inputs which will
> contribute.

I mute all inputs other than the "wave in"

In article <34a4f456.0403290055.2ca6aab3@posting.google.com>,
curious11112001@yahoo.com (Curious) wrote:
>
>It all occurs within the computer itself. No cables needed. The only
>thing "analog" is the end product, that is the signal the human ear
>can perceive. Before the d-a, the information is purely digital.

Most sound cards with which I am familiar do "wave to wave" using the D/A
and A/D convertors. The output of the D/A is also an input to the mixer,
which drives the A/D. So your noise is likely to be digital hash picked up
by the analog wiring on the sound card.

>I mute all inputs other than the "wave in"

That implies that the mixer has an input fed from the D/A, so it's further
evidence that your card is actually doing D/A - A/D.

-- 
Don Hills    (dmhills at attglobaldotnet)     Wellington, New Zealand
"I don't use Linux. I prefer to use an OS supported by a large multi-
national vendor, with a good office suite, excellent network/internet
software and decent hardware support."

Curious wrote:
> Why is it whenever I record from one wave file - at an extremely low
> volume - another wave file, I get noise?
>
> The process is completely digital. There is no analog, no D-A, and no
> A-D. Why the #%!$@%!@# is their noise?

Because the copying is not bit-perfect.

> Since this is not analog-to-digital, this is obviously *not*
> quantization noise.

Bad assumption. If your sound card resamples data, which many such as those
sold by Creative Labs do, then there is requantization, albeit entirely in
the digital domain.

> Quantization noise only occur during A-D conversion when the input volume
and/or bit-resolution is inadequate.

Wrong. Quantization noise is a consequence of quantization. Audio can be
requantized in the digital domain. It can happen without any A-D conversion,
or loss of volume.

However you are right about one thing - the noise is audible because the bit
resolution is inadequate.