[sci.electronics] New Lipshitz/Vanderkooy paper on digital audio

max@trinity.uucp (Max Hauser) (08/07/88)

I think this might be of interest to those of you interested in hard 
facts on digital audio and its technology.  It's posted separately
here from rec.audio to avoid spillage of the inevitable followups there.

Lipshitz and Vanderkooy, whose names will familiar to those who are
engineers interested in digital audio, presented a paper at the March
AES convention in Paris titled "Are D/A Converters Getting Worse?"  I 
obtained a preprint of this paper several weeks ago.  It is a massive 
report, 103 pages, the largest AES preprint by far that I have ever seen.
In it they compare exhaustively the technologies, electrical performance,
and particularly the low-level quantization effects in 17 CD players ("of
various vintages") and suggest that the audio performance in these, on 
the whole, is getting worse.  They include some experiments on distortion
audibility also.

What's most impressive is the enormous volume of supporting data in the
report.

The authors studied samples of the following players, though their data
are ordered chronologically by model release date:

	Sony CDP-35
	Sony CDP-101
	Sony CDP-200
	Sony CDP-302
	Sony CDP-310
	Sony CDP-350
	Magnavox FD1041
	Philips CD 650
	Technics SL-P7
	Yamaha CD-X2
	Yamaha CDX-500U
	Yamaha CDX-900U
	Yamaha CDX-1100U
	JVC XL-V400
	Denon DCD-600
	Denon DCD-800
	Nakamichi OMS-2

(I note with an element of professional delight that Lipshitz and
Vanderkooy emphasize a number of technical points, not heard nearly
enough, about digital audio that I have made repeatedly in this august
electronic forum; indeed these authors use enough of my favorite 
terminology employed in the last year of audio usenet postings to make 
me wonder just a bit ...  Even better, they avoid the annoying and 
confusing habit that many engineers have of referring to a "Hanning"
window for spectrum estimation (the correct and unconfusing name is
Hann), though I admit that this point will be of interest to very few.)

The conclusions?  Beyond the main one that I opened with, far too complex
to summarize here with any justice.  But the preprint is available for $4
from The Audio Engineering Society, 60 East 42nd Street, NY, NY 10165.

	S. P. Lipshitz and J. Vanderkooy
	"Are D/A Converters Getting Worse?"
	AES 84th Convention, Paris, 1-4 March 1988,
	preprint number 2586.

I would assume that they will have submitted it as a regular AES-journal
paper too, but the publication lag there is many months.

The authors do note that full-spec 16-bit digital audio performance,
especially with properly randomized quantization effects, is extremely 
good audio; all of the defects that they identify in their paper arise
from D/A converters that, in various ways, FAIL to meet the full spec.

Max Hauser / max@eros.berkeley.edu / ...{!decvax}!ucbvax!eros!max

"... and received an order from the Archbishop for a set of six duos."
(Dianne Nicolini, KKHI, 31 July 88, recounting a story of Mozart)

jshelton@zodiac.ads.com (John L. Shelton) (08/07/88)

I believe there was a summary of the Lipshitz/Vanderkooy paper in the
July issue of Stereophile. The summary indicated that a major problem
is that audio manufacturers are using D/A converters without making
the necessary trim adjustments; as a result, the D/As are not behaving
linearly.  The addition of $1 in parts, plus a little labor to make
the correct trimming would solve the problem.

=John=