The Truth About 'HD Audio'

[jonnythan]

Those super-special smart quotes don't work for those of us using the Western (ISO-8859-1) character set or ASCII. They come across as weird a's with circumflexes and Euro symbols.

 

[admin]

You know there’s trouble on the HD road ahead when Windex pitches a new formulation prefixed with the letters “HDâ€. And how about the marketing gurus at Kodak pitching “HD†photographic prints to counter the proliferation of digital photos, is this progress? Amidst the push for HDTV and heavy marketing of iBiquity’s so-called “HD Radioâ€, it should come as no surprise that the Consumer Electronics Association has rolled out a campaign to recognize and promote the improvement of reproduced music for consumers…AND that they’ve decided to call it “HD Audioâ€. It’s not high resolution anymore…a description that is more in keeping with existing verbiage. The audio community has jumped on the “HD†bandwagon.

Discuss "The Truth About 'HD Audio'" here. Read the article.

 

[WmAx]

That article.... sure, it has it's good points concerning the low standards of being able to qualify something as HD even if the source was not originally HD by definition. But there are some major leaps past this simple issue, in relation to the audibility claims made by the author. Does the author care to provide credible perceptual research citations to support the writer's bold assertion concerning sample rate and bit depth of CD being inadequate for playback purposes of music reproduction? The speculative, poorly-controlled A/B 'listening' test testament in the article does not qualify.

-Chris

 

[Dr. AIX]

A-B Comparison

Your point is well taken...my intention during the EHX show was not to carry out a double blind comparison between SD and HD audio reproduction. This was not the time or place for that level or testing. But because I have so many recordings that actually do have frequencies in the mid 30kHz range [as reported in Stereophile's analysis a couple of times] and because its a non-starter to be advocating for HD Audio if people cannot hear the difference, I took an award-winning track of ours [the Demmy winning "Mosaic" from Laurence Juber's Guitar Noir] and played it at both sample rates and word sizes. I was encouraged that using B&W 800Ds, Boulder Amps and Audience Cables...most of the people could tell there was a difference.

I have heard about a more rigorous test that Rupert Neve [of consoles and signal processor fame] carried out several years ago. He played a short frequency burst at 18 kHz first as a sine wave and then as a square wave. As traditionally portrayed, there should be no way to tell the difference...the second partial of the square wave would be at 36 kHz and there would no higher partials for the sine wave. If humans can only perceive frequencies up to 18-20 kHz, the two tone bursts should sound exactly the same...but the didn't. 85% of the assembled group could tell the difference. That's why he designs his electronics to pass up to 100 kHz. There is something going on beyond the traditional limits of our ears.

In reality, virtually all recordings that are placed on optical discs [CDs, SACDS and DVDs] do not contain frequencies that high and the dynamics are mastered for mass distribution. Music listeners do not get the opportunity to experience true HD source material in systems capable of reproducing it. But once presented with audio at that level, especially in surround [completely seperate topic], there's no going back. Personally, I cannot listen to 2-channel stereo CDs...regardless of the quality of the production. I've gotten spoiled by the HD Audio that we produce.

 

[WmAx]

I took an award-winning track of ours [the Demmy winning "Mosaic" from Laurence Juber's Guitar Noir] and played it at both sample rates and word sizes. I was encouraged that using B&W 800Ds, Boulder Amps and Audience Cables...most of the people could tell there was a difference.

And did you perform a full measure of known audible issues with the total loop of each system mode? Did you perform double-blinded testing? Number of trials? Statistical value ( p ) of these trials? These are just a few of the issues that are relevant.

I have heard about a more rigorous test that Rupert Neve [of consoles and signal processor fame] carried out several years ago. He played a short frequency burst at 18 kHz first as a sine wave and then as a square wave. As traditionally portrayed, there should be no way to tell the difference...the second partial of the square wave would be at 36 kHz and there would no higher partials for the sine wave. If humans can only perceive frequencies up to 18-20 kHz, the two tone bursts should sound exactly the same...but the didn't. 85% of the assembled group could tell the difference. That's why he designs his electronics to pass up to 100 kHz. There is something going on beyond the traditional limits of our ears.

Several highly credible labs have tried to find differences, and so far, when ever it has been put to highly controlled conditions that eliminate error(s) and/or bias that is present in the casual comparison, no difference has been found for music.

The closest was a work by [1] Oohashi(of questionable credibility) in the Journal of Neurophysiology(curiously, the paper was classified as an advertisement in the small print), and he claimed to have measured different brain patterns relative to the HD vs. standard audio bandwidth. Really, this was not about audibility, but sub-conscious brain activity. However, he also claimed audibility, and told loosely of a test he performed on the subjects to determine conscious detection. [2] NHK Labs tried to repeat his claim of audibility with a specialized speaker system and testing chain designed for this purpose, as well as a wide selection of listening subjects, and they failed to verify Ooashi's claims. Of course, all of this comes back down to the classic peer reviewed, highly credible, and standards setting work by Plenge [3]. No one has yet shown his work was in error. The only claims I have heard to the contrary are from those using comparisons that would never withstand a peer review in a journal such as the JAES.

I have performed my own trials upon myself using a computer along with ABX software, using samples that I carefully prepared. In regular A/B listening, I thought I could hear more "subtle detail' or 'air', I suppose you could call it, in the 96khz/24 bit HD samples. But when I put it to the real test in double-blinded, randomized testing, I could not discern any differences between the HD and the standard 44.1khz/16 bit audio version. My results were no better than chance.

-Chris

Footnotes
[1] Inaudible High-Frequency Sounds Affect Brain Activity: Hypersonic Effect
Tsutomu Oohashi, Emi Nishina, Manabu Honda, Yoshiharu Yonekura, Yoshitaka Fuwamoto, Norie Kawai, Tadao Maekawa, Satoshi Nakamura, Hidenao Fukuyama, and Hiroshi Shibasaki4
The Journal of Neurophysiology Vol. 83 No. 6 June 2000, pp. 3548-3558

[2] Perceptual Discrimination between Musical Sounds with and without Very High Frequency Components
AES Preprint: 5876
Toshiyuki Nishiguchi, Kimio Hamasaki, Masakazu Iwaki, and Akio Ando

[3] Which Bandwidth Is Necessary for Optimal Sound Transmission?
G. PLENGE, H. JAKUBOWSKI, AND P. SCHONE
JAES, Volume 28 Number 3 pp. 114-119; March 1980

 

[edmcanuck]

Great post WmAx, you've captured the issues perfectly. There are a number of claims in the article that simply have no support in the wide body of properly-setup research. Primarily, the bold assertion that "real life music" exceeds the bounds of 20Hz-22050Hz with a 96dB dynamic range in a way human beings can clearly discern. What real-life music is that? I think real-life and realistic and not being equated to one another here. Is it possible for music to exceed the CD specs? Yes. Is it likely? No. Would people be able to discern the difference when that music is recorded. All testing says no. The only claims to the contrary seem to come from people marketing a product.

 

[Rock&Roll Ninja]

I'm missing something. AIX produces only DVDs??

 

[mtrycrafts]

I have heard about a more rigorous test that Rupert Neve [of consoles and signal processor fame] carried out several years ago. He played a short frequency burst at 18 kHz first as a sine wave and then as a square wave. As traditionally portrayed, there should be no way to tell the difference...the second partial of the square wave would be at 36 kHz and there would no higher partials for the sine wave. If humans can only perceive frequencies up to 18-20 kHz, the two tone bursts should sound exactly the same...but the didn't. 85% of the assembled group could tell the difference. That's why he designs his electronics to pass up to 100 kHz. There is something going on beyond the traditional limits of our ears.

.

I question those protocols in the first place. How many in the audience, a poor way to establish anything worthy of discussion let alone being scientific, could in reality hear an 18kHz sine wave? Can you hear 18kHz? I bet not. And, even then, I'd ask what level is needed for threshold perception? Some young people can who has not been exposed to damiging levels of music.

There are several papers in Journals or Conference presentations showing that you just cannot hear it, unless the testing was flawed and IM was heard, not the above 20kHz fundamentals.

J Stewart of Meridian has published a paper on encoding needs where he indicated that at 20kHz, the threshold of detection is at 100dB spl.

Does your recording contain such levels of over 20kHz? Which speaker will reproduce it sufficiently above thresholds to be audible, if anyone can hear above 20kHz.

Claiming to hear the ultrasonic sound and making differences is nothing new but, so far nothing credible has been shown that this is indeed the case. Evolution was not kind to us. Or, it was as there was no need for such bandwidth in that time period.

 

[mtrycrafts]

Great post WmAx, you've captured the issues perfectly. There are a number of claims in the article that simply have no support in the wide body of properly-setup research. Primarily, the bold assertion that "real life music" exceeds the bounds of 20Hz-22050Hz with a 96dB dynamic range in a way human beings can clearly discern. What real-life music is that? I think real-life and realistic and not being equated to one another here. Is it possible for music to exceed the CD specs? Yes. Is it likely? No. Would people be able to discern the difference when that music is recorded. All testing says no. The only claims to the contrary seem to come from people marketing a product.

James Boyk did measure ultrasonic frequencies from instruments and shows it levels:
http://www.cco.caltech.edu/~boyk/spectra/spectra.htm

Note how quickly it drops off in level
The plot is tricky, so be careful when reading the sound level. Each gradient is different from chart to chart

 

[mtrycrafts]

Is that really the truth about HD audio, or a different marketing spin on it?

 

[Rock&Roll Ninja]

OK, so AIX sells DVD-A media.

 

[lowmagnet]

That was a somewhat underwhelming ad for AIX Records. Please post more technical articles and less puff pieces advertising for whomever wrote them.

People can't hear the difference between 24-bit and properly dithered 16-bit. This was proved by experimentation repeatedly in both professional and amateur ABXing. The average person can't hear above 18-19kHz. What's the point of HD if our hearing is to inferior to hear it.

 

[Dr. AIX]

HD Audio or Not?

My point in describing the current flurry of marketing efforts to appropriate the "HD" prefix was the point of the article. If CD quality in stereo is sufficient in its current implentation for the majority of readers then it would seem the development of audio engineering techniques, recording equipment and consumer delivery formats were perfected 30 years ago. I still believe that there is room for improvement and I'm encouraging the record industry to move to greater fidelity not less...which has sadly been the state of affairs over the past decade or so.

My experience is based on recording one of the largest catalogs of HD Surround Audio over the past 7 years. As I stated previously, I have not done the type of rigorous testing that would satisfy the AES journal but I have been a recording engineer for 25 plus years and am convinced that audio reproduction can do better than the CDs delivered today.

I'm on my way to London next week [and again in June] to present papers at their UK conferences. There seems to be a great deal of interest in HD Audio...I'll be happy to report on the research that is presented.

 

[tbewick]

If CD quality in stereo is sufficient in its current implentation for the majority of readers then it would seem the development of audio engineering techniques, recording equipment and consumer delivery formats were perfected 30 years ago. I still believe that there is room for improvement and I'm encouraging the record industry to move to greater fidelity not less...which has sadly been the state of affairs over the past decade or so.

I think the improvements made over the past thirty years to digital converters has allowed the performance with 16 bits to more closely reach the maximum theoretical levels available. Papers by people like Stanley Lipshitz and Louis Fielder have described audible effects due to converter designs eg.

'We find that the small-signal accuracy of the D/A systems of many currently available CD players [the paper was presented in 1989] is worse than that of models of a few years ago, and this applies even to some of the most expensive machines. The arithmetic design of many of the digital filter circuits in use is also suboptimal. We make the case that some of these defects are of sufficient magnitude to audibly degrade musical programs, and that proper low-level measurements including the use of dithered test tones should be used in the assessment of D/A converter systems.'

http://www.aes.org/e-lib/browse.cfm?elib=4820
Preprint 2586 (D-6) 'Are D/A converters getting worse?'. S.P. Lipshitz, University Waterloo, & J. Vanderkooy of Waterloo, Canada. Presented at the AES 84th Convention.

I also feel that the recording industry seems to get quite a hard press. The levels of compression in modern pop recordings are often criticised, but I think that it needs be recognized that this improves sound quality on some playback equipment. My experience with classical music leads me to believe that there are still plenty of well-recorded discs currently being produced.

 

[mtrycrafts]

What's the point of HD if our hearing is to inferior to hear it.

Marketing
The latest and greatest out there must be better
While those higher data rates may be beneficial in the mastering process, it is highly questionable for the home marketplace.

 

[mtrycrafts]

My point in describing the current flurry of marketing efforts to appropriate the "HD" prefix was the point of the article.

In that case, what is wrong with DVD-A? Or is that yesterdays marketing title and a new one is needed in light of the HD TV and HD soundtracks on it?

If CD quality in stereo is sufficient in its current implentation for the majority of readers then it would seem the development of audio engineering techniques, recording equipment and consumer delivery formats were perfected 30 years ago.

While some still prefer 2 ch, it was well known back in the 1930s that at least 3ch up front is needed and the advancements in multi channel has shown that is what is needed to better reproduce a live performance. So, that is not the issue here but the marketing of 'HD' that seems to be what D-A is about, or that ultrasonic is indeed audible and enhances the recorded music. That latter has not yet been demonstrated contrary to claims otherwise.

I still believe that there is room for improvement and I'm encouraging the record industry to move to greater fidelity not less...which has sadly been the state of affairs over the past decade or so.

That will be a tough sell considering that most of today's CDs are compressed to the hilt with hardly any dynamic range in there. Classical is a very small market share.
Perhaps what is needed is a better capture of the soundfield? Better mic locations? Better mastering folks?

..I'll be happy to report on the research that is presented.

Yes, please, we would like to hear what went on, what was presented, etc.

 

[Locke6854]

heres some food for thought

Whether you can consciously hear the difference or its your subconscious, think of this scenario:

When you walk by a bar and hear music playing, can you tell if its live music or a dj/recording? Most people can. Thats not to say that restaurants/bars/clubs have great audio systems.

The simple fact is we're trying to REPRODUCE sound. And it really doesnt matter how much you spend on your audio equipment, current cds dont sound like live instruments.

On a side, when I say "live" I'm obviously not referring to a "live" recorded cd, with a usually muffled far-away sound, and an audience cheer drowning out the instruments.

Not everyone has an ear that can tell the difference. Most of my friends can't tell the difference between mp3s or cds, but mp3 compression drives me crazy.

I think of it as a curse. Being an audio/videophile, and letting black levels, color banding, equalization, bass response etc bother you... I dont even like watching movies at other's houses because I'll be tempted to fiddle with their settings.

 

[mtrycrafts]

... current cds dont sound like live instruments.

And that is because a mic didn't capture all the soundfiled? Wasn't mic-ed properly? Sample high enough with equally high bit rate? Poor mastering?

I bet you don't remember long ago when they experimented with placing a speaker where a player was and let the speaker reproduce his instrument and swap back and forth, behind and acoustic curtain. Yep, no one could tell which was paling when.
Or, when John Dunlavy demonstrated his speakers with live sound. Yep, under his controlled conditions, it was another one of those misses.

I'd like to see a fair comparison between that HD recordings and the same mic being parallel fed to a lower sampling rate, or, even lower sampling from that HD recording. I bet it would be an interesting or not, outcome.

How is that HD different from a DVD-A recording? Certainly not the sampling and bit depth. Maybe, most likely, nothing.

 

[tbewick]

I thought it might be worthwhile to post a paper that examined the differences in digital filter performance at different sampling rates. I have referred to this paper before, but I think its inclusion in this thread is relevant. This quote is from the paper's conclusion:

'Linear and non-linear distortion mechanisms within digital audio FIR low pass filters used for decimation and interpolation have been described...The typical cosinusoidal passband ripple characteristic has been analysed to estimate the time-dispersion characteristics of the filter to signals within the audio band. This analysis is used to show significant differences in the pre and post-echo performance between the example filters.

Susceptibility of the filters to overshoot has been illustrated and the effect of compromises in stopband performance close to the folding frequency are discussed.

Filters designed for the higher sampling frequency of 96kHz are used to show how all these distortion mechanisms can be reduced by filters of similar computational requirements but with a more relaxed transition region. This results in either reduced ripple (and hence pre-echo) amplitude or in a lower time displacement for the echo.

In both cases the effect is likely to be a reduction in the audibility of the echo. A direct effect of the higher sampling rate is that for an identical filter design the time displacements will scale inversely with sample rate. Hence an improvement can be made just from raising the sample rate - even for those who cannot hear above 20kHz.

More work is required to evaluate the limits on the perception of the echo effects described here. This should cover both the audibility of echoes and their effect on the localisation of sound sources...The effects described here indicate that it may be difficult to distinguish any beneficial effects of an increase in sampling frequency from the different filter behaviour. This should be considered when making comparisons between different rates.'

http://www.nanophon.com/audio/antialia.pdf
Dunn, J. (1998). "The benefits of 96 kHz sampling rate formats for those who cannot hear above 20 kHz", Preprint 4734, presented at the 104th AES Convention, May 1998.