Ready for class

[tbewick]

I stumbled across this link while I was searching for something else:

http://ccrma.stanford.edu/courses/192a/

It's the homepage of the course 'Foundations of Sound Recording Technology', run by the Stanford University Department of Music. It covers (in pdf format) sound and electronics, microphones, amplifiers, digital sampling and recorders, and magnetic recording. I know it's a bit cheeky listing it here, but it's a freely accessible site open to anyone.

 

[mtrycrafts]

I stumbled across this link while I was searching for something else:
.

Isn't that how you find the interesting stuff?

I see they use Ken Pohlmann's book on Digital Audio

 

[tbewick]

Isn't that how you find the interesting stuff?

I see they use Ken Pohlmann's book on Digital Audio

One thing mentioned in the advanced class 192B (http://ccrma.stanford.edu/courses/192b/) disturbs me:

'One consideration is the possibility of CD amplitude causing distortion on some CD players. If the CD is mastered to full 0 dBFS, some analog output stages may overload due to D/A converter overshoot feeding into analog amplifiers with limited amplitude capability. The current trend in making louder and louder CDs contributes to this problem. Although everyone wants their CD to play louder than (or at least as loud as) all the other CDs, we should remember that playback systems DO have volume controls.'

- Jay Kadis, 'Compact Discs', p3-4.

I've also seen an update by Thomas Lund on this subject at the TC Electronics website -

http://www.tcelectronic.com/Default.asp?Id=9249&AjrThmPg=0

'Stop Counting Samples', which was presented at the recent AES convention in San Francisco. He follows up his earlier work in this area. I was doubtful at first as to how important this distortion could be, because it would only really affect highly compressed pop. In such recordings, owing to the large compression introduced by limiting, the distortion could be difficult to hear.

The levels of harmonic distortion he points to seem to be quite high, and differences in digital system design - particularly in the use of filters - will lead to different levels in distortion between players. Perhaps this could lead to audible differences between different systems? I know you've helpfully highlighted some tests between CD players before, i.e. -

- Pholmann, Ken C. '6 Top CD Players: Can You Hear the Difference?' Stereo Review, Dec 1988, pg 76-84. 'The New CD Players: Can You Hear the Difference?' Stereo Review, Oct 1990, pg 60-67.
- CD Player Comparison, The Sensible Sound, # 75, Jun/Jul 1999. # 74, Apr/May 1999.

Did the later tests use highly compressed CD's? Presumably when Pholmann's tests were done, compression levels on average weren't as high as they are today.

 

[mtrycrafts]

- Pholmann, Ken C. '6 Top CD Players: Can You Hear the Difference?' Stereo Review, Dec 1988, pg 76-84. 'The New CD Players: Can You Hear the Difference?' Stereo Review, Oct 1990, pg 60-67.
- CD Player Comparison, The Sensible Sound, # 75, Jun/Jul 1999. # 74, Apr/May 1999.

Did the later tests use highly compressed CD's? Presumably when Pholmann's tests were done, compression levels on average weren't as high as they are today.

The $ensible Sound didn't find differences. Hard to say what happened between 1988-1990 but I doubt compression was a practice then.

Interesting.

 

[tbewick]

The $ensible Sound didn't find differences. Hard to say what happened between 1988-1990 but I doubt compression was a practice then.

Interesting.

I actually remember reading somewhere, perhaps on Stereophile, how Ken Pholmann's given up on CD's. He's said to be very frustrated at the quality of new releases.

One other thing I was wondering was whether you'd looked at these AES papers:

J.R. Stuart, "Estimating the Significance of Errors in Audio Systems," presented at the 91st Convention of the Audio Engineering Society, J. Audio Eng. Soc. (Abstracts), vol. 39, p 1011 (1191 Dec.), pre-print 3208.

http://www.aes.org/e-lib/browse.cfm?elib=5508

and Chris Dunn's and Malcolm Hawksford's 'Towards a Definitive Analysis of Audio System Errors' presented at the same conference. This paper's available at Professor Hawksford's website at the University of Essex -

http://www.essex.ac.uk/ese/research/audio_lab/malcolms_publications.html

(Incidentally this site is very good, and has access to his work on amplifiers, loudspeakers, room equalisation, DAC's ADC's etc. and the 1992 convention paper on whether the S/P-DIF interface is flawed or not.)

I haven't got hold of the Stuart paper but the abstract sounded interesting, because it says that 'The paper addresses difficulties of A/B and nulling tests'. Stereophile actually called this paper 'seminal'. I believe that the perceptual method used in the paper might have been used in analysing jitter audibility that I posted a while back. I remember you asking about how they did the 120 dB SPL audibility tests?

 

[mtrycrafts]

I actually remember reading somewhere, perhaps on Stereophile, how Ken Pholmann's given up on CD's. He's said to be very frustrated at the quality of new releases.

One other thing I was wondering was whether you'd looked at these AES papers:

J.R. Stuart, "Estimating the Significance of Errors in Audio Systems," presented at the 91st Convention of the Audio Engineering Society, J. Audio Eng. Soc. (Abstracts), vol. 39, p 1011 (1191 Dec.), pre-print 3208.

http://www.aes.org/e-lib/browse.cfm?elib=5508

and Chris Dunn's and Malcolm Hawksford's 'Towards a Definitive Analysis of Audio System Errors' presented at the same conference. This paper's available at Professor Hawksford's website at the University of Essex -

http://www.essex.ac.uk/ese/research/audio_lab/malcolms_publications.html

(Incidentally this site is very good, and has access to his work on amplifiers, loudspeakers, room equalisation, DAC's ADC's etc. and the 1992 convention paper on whether the S/P-DIF interface is flawed or not.)

I haven't got hold of the Stuart paper but the abstract sounded interesting, because it says that 'The paper addresses difficulties of A/B and nulling tests'. Stereophile actually called this paper 'seminal'. I believe that the perceptual method used in the paper might have been used in analysing jitter audibility that I posted a while back. I remember you asking about how they did the 120 dB SPL audibility tests?

I would be careful with Hawksford's papers. Stereophile had his Essex Echo paper that is grossly flawed. Jneutron tried to discuss that with Hawksford but would not participate in such a discussion. I would also suspect Stereophile.
I don't have Stewarts paper. Him, and his work, I respect

Benjamin at Dolby has an AES paper on jitter audibility:
Benjamin, Eric and Gannon, Benjamin ' Theoretical and Audible Effects of Jitter on Digital Audio Quality,' 105th AES Convention, 1998, Print 4826.
That I have, not the others. You need a lot of jitter to have it audible. Such high levels usually just not measured from components.

Yes, many of today's CD is over compressed. WmAx has so indicated this himself here that he measured.

 

[tbewick]

I would be careful with Hawksford's papers. Stereophile had his Essex Echo paper that is grossly flawed. Jneutron tried to discuss that with Hawksford but would not participate in such a discussion. I would also suspect Stereophile.
I don't have Stewarts paper. Him, and his work, I respect

Benjamin at Dolby has an AES paper on jitter audibility:
Benjamin, Eric and Gannon, Benjamin ' Theoretical and Audible Effects of Jitter on Digital Audio Quality,' 105th AES Convention, 1998, Print 4826.
That I have, not the others. You need a lot of jitter to have it audible. Such high levels usually just not measured from components.

Yes, many of today's CD is over compressed. WmAx has so indicated this himself here that he measured.

I have downloaded several of Hawksford's papers but haven't had enough time to read them yet. He cites Stuart's 'Estimating the Significance of Errors in Audio Systems' paper in his 1994 AES conference paper 'Digital-to-Analog Converter with Low Intersample Transition Distortion and Low Sensitivity to Sample Jitter and Transresistance Amplifier Slew Rate'. To be fair he is a professor and an AES fellow, so I wouldn't feel comfortable criticising he work.

I do see your point in that some of his references are to non-academic works, like Stereophile and Hi-fi News. I won't say however that this is all that usual. I remember reading another paper - it could have been an AES one - where the author says that 24 bit/192 kHz is considered truly transparent, or something like that. In his references section, all he says is that he was told this in an e-mail correspondence!

Hawksford's '94 paper says in the abstract that it presents a DAC design with low jitter sensitivity.

The jitter paper Chris referenced -

'A Jitter Simulator on Digital Data', Preprint Number:5390, Convention:110 (April 2001) Authors: Ashihara, Kaoru; Kiryu, Shogo
http://www.aes.org/e-lib/browse.cfm?elib=9976

These authors were involved in a later paper, which states:

'Benjamin and Gannon [1] made an attempt to measure thresholds of audibility for sinusoidal jitter on program materials. Their study seems to have a few problems, however. In their study, a special arrangement was made to the reproduction system in order to add jitter at the digital interface. It is not known if such an arrangement might change sound quality and affect the results. Secondly, they employed a selfadministered threshold evaluation in which the listeners determined their thresholds at their discretion. Their results might contain errors due to the cognitive factor.'

- Ashihara, K. et al. 'Detection threshold for distortions due to jitter on digital audio', Acoustical Science and Technology, Vol. 26 (2005) , No. 1 pp.50-54. Freely available for download at http://www.jstage.jst.go.jp/article/ast/26/1/26_50/_article

Again, I haven't read the full paper yet, but the abstract appears to point to a similar conclusion as the earlier Dolby paper - 'It was shown that the detection threshold for random jitter was several hundreds ns for well-trained listeners under their preferable listening conditions'.

 

[mtrycrafts]

... To be fair he is a professor and an AES fellow, so I wouldn't feel comfortable criticising he work.
.

Me neither but John sure had no problem

http://www.audioasylum.com/forums/prophead/messages/1811.html

And, there may be nothing wrong with his other works.

I wonder if that author contacted Benjamin or Gannon about his issues with the paper? And it goes on an on
Not solved here.

 

[tbewick]

Me neither but John sure had no problem

http://www.audioasylum.com/forums/prophead/messages/1811.html

And, there may be nothing wrong with his other works.

I wonder if that author contacted Benjamin or Gannon about his issues with the paper? And it goes on an on
Not solved here.

Thanks for the link.

I have had trouble getting hold of Martin Colloms' writings for Hi-Fi News which are cited by Malcolm Hawksford. Some of Martin Colloms other writings have left me stunned:

'Metallurgy: Many establishment audio engineers consider that Ohm's Law is wholly sufficient to describe current flow in a wire, and that all metallic conductors must sound the same owing to the fundamental property of free electron mobility in this class of material. However, there is now strong evidence to indicate that the choice of element or alloy for a conductor, its metallurgical history, and its absolute purity all affect the sound quality. This finding, unwelcome for those working in this field, cannot be ignored. It seems a cruel twist of fate that of the many conducting materials tried, high-purity silver sounds the most accurate, as it costs approximately 100 times as much as the substantially effective and most widely used material available: copper.

Some physicists approached on this subject have invoked quantum theory to analyze the behavior of metallic conductors in varying states of practical purity, particularly with respect to the boundaries between metallic crystals.'

- http://www.stereophile.com/asweseeit/190/index6.html

Certainly there are physical scientists who have developed models that relate macroscopic observables like current, charge, etc. to microscopic quantum theory through the Fermi level etc. but to suggest that the voltages and currents used in audio signals are significantly affected by quantum effects defies belief. I wonder if Colloms knows of the typical energy level separations of states in a copper/silver wire. What signal-to-noise level would you need in order to discern this? Surely it is beyond all experimental science. Perhaps he is of the view that if you keep walking into a wall you'll eventually pass through it because of quantum tunnelling?

 

[mtrycrafts]

.... Perhaps he is of the view that if you keep walking into a wall you'll eventually pass through it because of quantum tunnelling?

Yes, of course. Why didn't I think of this before. I just wonder if I will live long enough for this to happen for a practical application, like eliminating doors and thereby making my home more energy efficient

As you can see, these associations of Hawksford and some kooks, doesn't bode well for his credibility and one must be well versed in the subject to know when he is off the deep end and when he is not

By the way, if you'd followed Jneutron's (john escalier)postings over his posting life, I think he posted on that grain and crystal boundary stuff as the prophet Jon Risch is a big advocate of that silliness.