kalessin wrote: > Hi, > > I came across this test when a member in a different forum (Pianoteq) > mentioned it. They also claimed to be able to pick out the 24bit samples > without guessing with 100% certainty, and this made me curious. So I > acquired the test data and had a look. After doing my own (failed) > listening test, I could however not just disregard the claim of the > other forum member, as they absolutely ruled out any guessing was > involved. So... I looked closer. > > To cut a long story short, I found certain flaws in the test data, > likely due to a problem in processing. Because of this, I would not be > surprised if a statistically significant number of listeners were able > to hear differences between the files. For example, I can discern very > clearly between the files when looking at their spectra even after > downsampling to 44/16. And this is something I should not be able to > do. > > You can try this for yourself. Take the Vivaldi sample (the real 24bit > one), and export it to 16bit using Audacity. Be sure to use the > high-quality settings and e.g. the triangle dither. Then re-import it > into Audacity. Now pick e.g. a two-second window and run a FFT analysis. > You can see the differences directly; however, the dithering noise is > very low and only really visible in the high frequency range (>20kHz), > where the original file has virtually no spectral power. This is to be > expected. > > Now comes the trick. Convert both samples (the original and the 16bit > conversion) to 44.1kHz and look at them again. When I do this here > (since Audacity -does- the conversion correctly, at least in its > highest-quality mode), all differences between the spectra more or less > vanish completely, especially when looking at frequencies of 16kHz and > below; this is also to be expected. Thus when I do these steps in > Audacity, the dithering indeed only affects the highest frequencies, > since they are the weakest. > > Soo... and now we have a look at that 'B' sample. Again choose an > analysis window, e.g. 1:23 to 1:25. Take care to shift it 1ms to the > left to compensate for the 1ms cut as documented. Look at it in 96kHz. > Already -lots- of differences between A and B, even in low frequencies > and at relatively high levels. Convert it down to 44.1kHz. Be amazed at > how different the spectra still look. The differences are subtle, but > they -are- present, and as I mentioned they cover the whole spectral > band, including the lower frequencies. Although -my- ears might be > rubbish, I am absolutely not surprised that someone with good hearing > can hear those differences. > > The problem I have with this is that when I accept the sampling theorem, > which I do (both as a physicist and a programmer), then any > 'improvement' a 96/24 or 192/24 recording offers has to happen either at > very low levels or at high frequencies, since -everything- from -96 to > 0dB and from 0 to 22kHz is encoded losslessly. So it is indeed a very > important baseline test that both the original 24bit and the dithered > files in a comparison test yield a (virtually) identical result when > converting down to 44/16. Audacity manages this quite well. The used > version of Adobe Audition does not, it seems.
Interesting comment. I must admit I'm not much of an Audacity user so am not familiar with what Audacity is doing in those 24 <--> 16-bit conversion steps. However, I just downloaded Audacity to this workstation and had a quick look. As far as I can tell, Audacity uses a noise-shaped dithering by default even when I set it to triangular mode in the preferences and export to 16-bits. Also, I don't know if I can set the strength of dithering being applied in Audacity. Like I said, I'm not an Audacity guy but am suspicious that you're seeing the difference between a very low 0.5 bit flat triangular dithering (what I did with Audition) with the noise shaping characteristics of Audacity which would start showing differences below 20kHz when converted to 16/44... Archimago's Musings: (archimago.blogspot.com) A 'more objective' audiophile blog. ------------------------------------------------------------------------ Archimago's Profile: http://forums.slimdevices.com/member.php?userid=2207 View this thread: http://forums.slimdevices.com/showthread.php?t=101742 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
