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Old 18th August 2013, 09:40 PM   #1
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Default A silly question about sampling ...

Is the process of audio sampling a->d deterministic ? In other words if I play a vaw for example out from my dac and then acquire the analog out with a analog to digital converter more and more times, the file obtained are bit to bit identical ?

I think not, so i am curios about how different could be, even if I do not know nere and now a tools to compare the difference; perhaps the conversion can be made in wav so a proper audio tools can extract the diff.

I ammon holidays without tools to inspect ... but curiosity is high ...

I apologize for my bad english and for the silly question, I am searching a tools to inspect the difference between different digital source ...

Mauro
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Old 18th August 2013, 09:59 PM   #2
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Hi Mauro, if you do a D/A conversion and then A/D then yes each time you do it you will be altering the signal from the original. If you do it multiple times the error will compound.

I've not tried it but have seen it mentioned here a number of times. but audio diffmaker seems to be what you are after. Audio DiffMaker

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Old 18th August 2013, 10:05 PM   #3
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In theory, all versions of the file would be identical. In practice, they would all be different. Subsequent A to D conversions would include what ever noise was present in the analog domain. The D to A conversions would, most likely, have added dither, which is digital noise. So, each generation would have additional noise.
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Old 18th August 2013, 11:07 PM   #4
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Mauro, I think you might have misapplied your concept of determinism and presented yourself with a false dichotomy.

Could you explain what you mean by "deterministic", please, and how you distinguish it from "precise"?
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Old 18th August 2013, 11:13 PM   #5
Pano is offline Pano  United States
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As Tony says, try DiffMaker.

Hint: your copies will not be bit perfect, but they will be close.
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Old 18th August 2013, 11:21 PM   #6
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no analog channel is "deterministic" if you mean noise free

you may be thinking about what some call "generation loss" - put a signal thru some number of record/measure/playback/rerecord.. cycles and see how the signal changes

any purely analog scenario - say studio tape recorder, EQ, lacquer cutting, needle drop, preamp with inverse EQ back to tape... chain is going to be laughably worse than most motherboard digital audio chipsets


but even really good audio ADC/DAC aren't going to give bit perfect loopback because of gains, scale factors, offsets, filters all have tolerances orders of magnitude worse than even 16 lsb resolution

Last edited by jcx; 18th August 2013 at 11:25 PM.
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Old 18th August 2013, 11:31 PM   #7
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In practice you will almost certainly not get a bit perfect copy, but... it could be arranged for you to do so, especially if the ADC and DAC were of low resolution and synchronised in their timing.

Some of the earliest computer memories were based on continuous recirculation of acoustic pulses in delay lines and relied on the pulses being received at one end and re-transmitted at the other, effectively by a 1-bit ADC and DAC, so a 'bit perfect' copy was essential.

Delay line memory - Wikipedia, the free encyclopedia
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Old 18th August 2013, 11:57 PM   #8
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Also shocking how good digital really works is this insane 60 generations D/A -> A/D conversion.
Zmix Converter Tests
If you listened and think about it you may have another view about what is really important...
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Old 19th August 2013, 08:13 AM   #9
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Default Well ...

Thanks to all for the reply ...

wintermute

Audio DiffMaker is the tool I am searching for ... I will experiment with this ...

PlasticIsGood

I do not know the exact English meanigs of "deterministic", I have directly translate the word that in Italian I use in math/phys way ... "a finite system with well known initial state and subsequent state transformation ..."

In my case the same wav file, the same hardware, the same (more or less) condition (temperature, supply voltage, rf noise ... etc ...); if the system is deterministic the result file must be identical bit to bit ...

Is obvious that the the condition do not be costant so there will be different result but I want to investigate HOW different can be ... non from a infomatical prospective (two file with 1 bit different are completelly different) but from an psychoacoustics prospective ...

I need to compare a lot of source chain with the "absolute ear" of a friend but I cannot test every change made with live a/b/x test with him (for logistics evident problems ...)

So I am trying to reconvert ALL the test in digital from analog an submit all the digital result to him in a simple a/b/x test ... I am curios to compare what he can "ear" with instrumental relevated difference ...

I will pass the Audio DiffMaker to an FFT analysis to compare the human hearing response with the instrumental perspective of the same difference ... if all is not the noise level of course

The unique other way is remain in analog but I have to transport to my workshop one of a very BIG high quality tape recorder that we own ... but is a complete different story
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Old 19th August 2013, 08:48 AM   #10
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What are we meaning by bit perfect? The thing is that a perfectly sampled copy of a waveform but with an arbitrary delay will not be bit perfect when you look at the two files i.e. the numbers in the two files will be completely different - and I don't mean simply not aligned. However, the delay could be removed in software to get you back to a bit perfect copy (or almost).

This is a great video explaining how 'bit perfect' similarity between digital recordings is not likely to be achieved, but nor is it important in determining the quality of your copy.

Xiph.Org Video Presentations: Digital Show & Tell
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