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Vinyl -> Digital
cliveb
post Dec 15 2010, 10:44
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QUOTE (LocrianGroove @ Dec 15 2010, 03:36) *
Has anyone done any testing to determine the minimum number of bits required for a digital recording to sound the same as a vinyl recording?

I just did a very casual test using small section of a typical vinyl rip that I did some time back. The original rip was made at 16 bits with an M-Audio AP2496 soundcard. (The turntable/arm/cartridge/preamp was Linn LP12/Ittok/Karma/Naim NAC42.5). The LP was a fairly typical album from my collection - not a test record or "audiophile" pressing, but a normal album in good condition. I deliberately chose a section that was fairly quiet (final part of a tune with delicate piano and tinking cymbals).

I prepared the reduced bit depth samples by cutting the amplitude by 6dB and then raising it back by 6dB. Each such cut/boost cycle gives a 1 bit reduction (as near as makes no odds). I did all this at 16 bit without dither to provoke approximately the same sort of quantisation noise you'd get with native recording at those bit depths.

It was trivially easy to hear the difference between 16 bit and 11 bit - ABX log follows:

CODE
foo_abx v1.2 report
foobar2000 v0.8.3
2010/12/15 09:23:00

File A: file://C:\clive\audio\The Guest Stars\Out At Night\x11.wav
File B: file://C:\clive\audio\The Guest Stars\Out At Night\x16.wav

09:23:00 : Test started.
09:23:33 : 01/01  50.0%
09:23:37 : 02/02  25.0%
09:23:40 : 03/03  12.5%
09:23:48 : 04/04  6.3%
09:23:55 : 05/05  3.1%
09:23:59 : 06/06  1.6%
09:24:03 : 07/07  0.8%
09:24:06 : 08/08  0.4%
09:24:12 : 09/09  0.2%
09:24:18 : 10/10  0.1%
09:24:20 : Test finished.

----------
Total: 10/10 (0.1%)


I could not tell the difference in an ABX between the 16 bit and 12 bit versions. Note that I was doing this test on a laptop with a not especially sophisticated audio path, using fairly run of the mill headphones (Sennheiser 435). Therefore I think it is conceivable that it might be possible to distinguish the 12 bit version with better playback equipment and/or other music samples.

So: how does this answer the question of the minimum number of bits needed to transparently record an LP? Well, my argument is that if there is no difference between 12 and 16 bits, adding still more isn't going to help. My conclusion is that 13 bits is probably enough to faithfully record typical vinyl sources, although you'd then have to be very careful about recording levels to ensure you actually made use of all 13 bits.
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LocrianGroove
post Dec 15 2010, 19:05
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QUOTE (kraut @ Dec 15 2010, 01:11) *
QUOTE
We've been doing the calculations based on the SNR of the medium (e.g. 12 bits for a ~72 dB SNR)



I have the test record by Floyd Toole, with excellent Dynamics, and other studio test records..
The typical level of the noise floor running the test record is about -40db with a well running thorens td 125 and a denon dl 160 on an SME III arm. Where do you get the -72 db from?


Good question. The -72 dB does not reflect data. I used it as a hypothetical number for a dynamic range calculation, which is why I was careful to write "(e.g. 12 bits for a ~72 dB SNR)," instead of "(i.e. 12 bits for a ~72 dB SNR). Sorry for not stating that more explicitly.
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LocrianGroove
post Dec 15 2010, 19:13
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QUOTE (cliveb @ Dec 15 2010, 04:44) *
It was trivially easy to hear the difference between 16 bit and 11 bit - ABX log follows:


QUOTE (cliveb @ Dec 15 2010, 04:44) *
I could not tell the difference in an ABX between the 16 bit and 12 bit versions.


Interesting. Thanks for doing the experiment.
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Brod
post Feb 9 2012, 07:26
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QUOTE (Juha @ Dec 13 2010, 12:55) *
To test if the resulting samplerate is 96 just record something and then check with some spectrum analysis software (as for an example, iZotope RX http://www.izotope.com/) if the frequency range goes beyond 22.05 kHz.


You're confusing low-pass filtering with sampling rate - the two things are not related.
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pdq
post Feb 9 2012, 18:14
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QUOTE (Brod @ Feb 9 2012, 02:26) *
QUOTE (Juha @ Dec 13 2010, 12:55) *
To test if the resulting samplerate is 96 just record something and then check with some spectrum analysis software (as for an example, iZotope RX http://www.izotope.com/) if the frequency range goes beyond 22.05 kHz.


You're confusing low-pass filtering with sampling rate - the two things are not related.

I think the point was that if the samplerate was 96 kHz then there may (and probably will) be frequencies above 22.05, but if the samplerate was 44.1 then there can not be frequencies above 22.05.
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greynol
post Feb 9 2012, 18:52
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QUOTE (Brod @ Feb 8 2012, 22:26) *
You're confusing low-pass filtering with sampling rate - the two things are not related.

I guess we need not concern ourselves with aliasing.

I recommend you study up on sampling theory before resurrecting dead discussions in a clueless attempt to strike down legitimate information.

This post has been edited by greynol: Feb 9 2012, 19:01


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Brod
post Feb 10 2012, 08:46
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There's no such thing as a dead discussion - this is a forum. If you disagree with what I said then I welcome a refutation, as long as it's civil.
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Canar
post Feb 10 2012, 08:51
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QUOTE (Brod @ Feb 8 2012, 22:26) *
QUOTE (Juha @ Dec 13 2010, 12:55) *
To test if the resulting samplerate is 96 just record something and then check with some spectrum analysis software (as for an example, iZotope RX http://www.izotope.com/) if the frequency range goes beyond 22.05 kHz.
You're confusing low-pass filtering with sampling rate - the two things are not related.
No he isn't.

QUOTE (Brod @ Feb 9 2012, 23:46) *
There's no such thing as a dead discussion - this is a forum. If you disagree with what I said then I welcome a refutation, as long as it's civil.
pdq refuted you nice and succinctly. Of course, even entry level signal processing / EE training would disabuse you of the tangent you're trying to drag this thread off into.


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