44.1 vs 88.2 ABX report at AES Options

[2Bdecided]

Here:

http://www.aes.org/events/128/papers/?ID=2252

P18-6 Sampling Rate Discrimination: 44.1 kHz vs. 88.2 kHz—Amandine Pras, Catherine Guastavino, McGill University - Montreal, Quebec, Canada
It is currently common practice for sound engineers to record digital music using high-resolution formats, and then down sample the files to 44.1 kHz for commercial release. This study aims at investigating whether listeners can perceive differences between musical files recorded at 44.1 kHz and 88.2 kHz with the same analog chain and type of AD-converter. Sixteen expert listeners were asked to compare 3 versions (44.1 kHz, 88.2 kHz, and the 88.2 kHz version down-sampled to 44.1 kHz) of 5 musical excerpts in a blind ABX task. Overall, participants were able to discriminate between files recorded at 88.2 kHz and their 44.1 kHz down-sampled version. Furthermore, for the orchestral excerpt, they were able to discriminate between files recorded at 88.2 kHz and files recorded at 44.1 kHz.
Convention Paper 8101

Was anyone at the presentation? Has anyone bought the paper?

Cheers,
David.

[AndyH-ha]

It seems that what I wrote in the first part of my post here has been addressed since I read the thread, but the second part still might bare consideration.

I’m not following the discussions about brick-wall filters since I am under the impression that the majority of modern audio converters are some version of delta-sigma, which does not use such filters. Actual sample rates are high, 64X and 128X being typical, with digital decimation being used to achieve the final sample rate and prevent aliasing. The front-end analogue filters are described at “rather mild,” far short of what would be required to prevent aliasing in an non-oversamplng design.

My main reference is copyright 2000 (Ken Pohlmann’s Principles of Digital Audio, 4th edition), so something might have changed in this regard recently, but I’ve never seen anything about it. Is the discussion about brick-wall filters aimed at a special market or do I have some basic misunderstanding on this topic?

I would also like to throw something more into the discussion. Maybe explicit recognition of it could lead to some way to account for it in the testing. I’ve written about it in two earlier threads. Possibly some of the links to screen shots still exist in one of those.

I generated a sweep frequency signal at 88.2kz, covering the entire available frequency range. Playing it out the DAC of one soundcard and into the ADC of another, I found that I got back something very close to what was initially generated in CoolEdit (except with a SB Live).

Then, playing it at 88.2 and recording at 44.1kHz, I found a definite alias image. For the first couple kHz below the Nyquist Limit, hen recording at 44.2kHz, the image was quite strong. If I turned up the resolution in CoolEdit’s Spectral View, I could see the alias trace almost to zero Hz. Resampling the generated sweep tone in CoolEdit from 88.22 to 44.1 produced none of the aliasing.

I tested several reputable sound cards. All were the same (except the SB, which was much worse). When I initially posted these results in another forum there was a lot of noise about my failures until a couple of people with more expensive professional converters duplicated my results. This happened again later in another forum. While this is still only a small sample of all soundcards, I suspect they all do the same.

As discussed earlier in HA, I don’t think this is a significant audio defect. Certainly I cannot hear any distortion that may be produced, especially at 20kHz and above. Very little music has much content at the higher frequencies necessary to produce such aliasing anyway, and any such hf is likely to be rather low in intensity.

Still, this does make for a real difference in recording at higher sample rates vs. 44.1kHz. Aliasing cannot be removed from the recording. Since the alias image is only very strong (relative to the input signal) for a couple of kHz below the Nyquist Limit (meaning about 42kHz to 44kHz at a sample rate of 88.2kHz), even the little distortion that might be present in 44.1kHz recordings will be absent at 2X that, and above.

[googlebot]

AndyH-ha, that might be on purpose. For two lowpass filters of identical computational complexity, with A being allowed to inject more imaging above f than B, et ceteris paribus, A has potentially higher passband performance (0-f Hz) than B.

This post has been edited by googlebot: Jul 17 2010, 10:53