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

Started by Curious March 27, 2004
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? -- % Randy Yates % "Rollin' and riding and slippin' and %% Fuquay-Varina, NC % sliding, it's magic." %%% 919-577-9882 % %%%% <yates@ieee.org> % 'Living' Thing', *A New World Record*, ELO http://home.earthlink.net/~yatescr
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.