16 bit vs 24 bit, any samples that work? Options

[AndyH-ha]

There are real differences between 16 bit and 24 bit files, just as there are real differences between uncompressed and mp3. As with the differences between wav and mp3, 16 bit vs 24 bit is often difficult to identify by listening.

Test signals are one thing, but has anyone found any 24 bit music recording that can be successfully identified via ABX testing against a properly resample to 16 bit version of same?

[Pio2001]

Hello,
In september, I did an ABX between a 96 kHz 24 bits file and a 44.1 kHz 16 bits one, made by Voxengo R8brain from a 192 kHz 24 bits file from 2L (the Mozart one) : http://www.2l.no/hires/index.html (you can even download a 352 kHz 24 bits DXD version and a 2.8 MHz DSD version !)

Voxengo's software says that 8-, 16- and 24 bit output is dithered with a gaussian noise and a slight noise-shaping. I have no idea if it is the proper way to do it.

The original account is here : http://www.homecinema-fr.com/forum/viewtop...59&start=60

It's part of an epic 24/96 ABX challenge in which a forumer fell from an "obvious, huge, unmissable" difference just before the ABX test, to a complete failure !

I got 10/10 in the ABX test, with closed headphones, listening to the initial fade-in. Comparing the playback level to speakers, and using a sonometer, I think that the listening level was such that the 0dB of the digital scale was at 113 dB(A) on a white noise. Since the track has a peak level of -1 dB and an RMS level of -23 dB, the listening level of my ABX test is something like 90 dB RMS, with peaks at 112 dB.

The use of closed headphones, that isolate from the environment, especially the computer noise, is useful. I also had to "release" the internal pressure in my ears (like divers) several times in order to stay at the top of my sensitivity.

What is interesting is to compare the quantization noise to the file content. By ascending order, there is :

-The 16 bits noise. Without this ABX test, I would never have thought that it was audible
-The background noise of the microphones and of the recording location. The 16 bits noise doesn't seem to be completely masked.
-The breathing and movements of the musicians, far above the previous
-The music, still far above.


Playback system : Foobar2000 v0.8 in 24 bits mode (note that this version used to equalize the RMS levels of files to be ABXed).
Marian Marc 2 soundcard, analog output, MME drivers, Windows XP (Waveout, MME device in Foobar).
Superex Pro-B VI headphones.

[Kees de Visser]

I got 10/10 in the ABX test, with closed headphones, listening to the initial fade-in.

There you go ! During the fade-in the noise level of the recording is probably too low to mask the 16-bit dither. IMHO the crucial condition for audibility is that the level of the added (dither) noise is relatively high compared to the noise level of the source. During digital silence (no modulation) or fade-ins/outs this condition is met, so with enough monitoring gain the noise difference can be easily made audible. The cumulative noise of the hall/studio, microphones and pre-amps is likely to be the most important source, usually with a gaussian spectrum. Most dithers use white noise, which has a slightly more aggressive character compared to gaussian, so predicting masking isn't very easy.
Pio, most classical recordings have "room tone" (acoustical noise) between the movements. Could you redo your test by using such a fragment without fades ? Note that there are recordings where this "silence" has been lowered somewhat in level so it doesn't necessarily have the same masking properties as the noise during the music.