There are a lot of claims made by DAC manufactures of better fidelity, low jitter etc. Is anyone aware of any rigorous tests of any of these claims? Any abx studies of the difference of various DACs?

We ABXed two analog copies : one from a California Audio Labs CD player, and another from a Panasonic Discman : http://www.homecinema-fr.com/forum/viewtop...rt=45#169355556

The discman pitch plays 1/30th of a tone too high (0.4 % too fast)

Interesting. Is that what enabled you to abx it? (My french is very poor).

No, I didn't realize that the pitch was different. There is one more dB of treble in one sample, and there is a noise in the 4th and 6th notes of the main theme that is more audible in one sample.
I did not know that the first samples were not level matched, but as far as i remember, I used Foobar2000 0.8.3 for the test, and it automatically matches the levels.

Was the ADPCM compression of Panasonic CD player turned off? Current models have the ability to turn off this skipping protection mechanism as it known to affect sound quality, especially with synthetic test tones.

Edit.

What was the model number? I think that it is possible to disable anti-skip protection. (Je ne parle pas français. )

Thanks to Pio2001 and Google Translate for translations.

QUOTE (GBo at homecinema-fr.com @ Jan 30 2006, 07:39 AM)

Salut, et bien le bonjour à Egor.
C'est un Panasonic SL-MP50. 
Par contre j'ai oublié de dire qu'il n'a pas de line out, j'ai du utiliser la sortie casque pour la capture analogique, ce qui explique peut-être les bizarreries de dynamique voire une partie des distorsions mesurées. Par contre ça ne change rien à la différence de pitch (hauteur) qui est suffisamment importante pour trahir son idendité en comparaison directe (en tout cas pour mes oreilles).
cdlt,
GBo

Hello, GBo.
SL-MP50 is a model of year 2002 and (unfortunately!) it doesn't support disabling anti-skip ADPCM compression.

Distortions did appear due to lossy ADPCM compression applied before streaming to anti-skip memory, not because you had used headphones output to perform measurements. Therefore your Panasonic CD player's DAC test is a bit unfair, as it doesn't show actual DAC quality. More recent models (e.g. my SL-SX428 and SL-CT820) have larger anti-skip memory and support Audio CD playback without any lossy compression (which however is turned on by default).

Thank you for the information.

It's funny how listening works. Gbo did not perceive the compression, but the pitch difference, while I did the opposite.

Indeed, especially people with "absolute pitch" will notice the pitch difference sooner than "normal" people.
In my experience, pitch differences between digital audio devices are always caused by different clock rates. For most consumer equipment the clock will be derived from the internal crystal and there you will find quite some tolerances.
I remember the days when cdr wasn't yet available so we had to send mc (cassette) copies to the artists for approval. Pitch differences were often a problem. With modern digital audio it should be fine but apparently that is not always the case.
Did you check the clock frequency of the playback device, e.g. with an oscilloscope or frequency counter ? The crystal might have been out of spec.

No,
However, checking today that thread, it reminded me that the original experiment was a positive ABX (8/8) between two analog copies, one from a DVD player, the other from the same DVD player + an external DAC : http://www.homecinema-fr.com/forum/viewtopic.php?t=29803639

It seems to me that the ABX test was hardly necessary since there definitely seems to be something broken. A DAC that changes pitch should be returned to the designer, unless it's a documented feature.

A DAC doesn't change pitch. The pitch was changed by the portable player. But here I speak about the ABX between the copy from the DVD Player and the copy from the DVD Player + the DAC. There was no pitch change here, and only GBO managed to pass the ABX.
There were also some other ABX successes, but these ones come from the fact that the CD had pre-emphasis turned on, and only some players were applying the de-emphasis.

OK, thanks for clarification. I must have misread.



O dear, do cd's with emphasis still exist ? These days most mastering engineers remove the emphasis to avoid this kind of problem. I hope it was an old cd :)

Yes, it was an old CD