wjm@whuxk.UUCP (MITCHELL) (01/04/84)
The most recent (Jan. 1984) issue of "Audio" ought to add more fuel to the digital vs analog debate. It contains an interview with Doug Sax and Lincoln Mayorga of Sheffield Labs, and their comments (and reservations) about digital recording. Given their background and the type of recordings they produce at Sheffield, their words should certainly be considered heavily. The same issue of "Audio" also discussed the myth behind the apparent difference in dynamic range (analog 70-80 dB to digital's 90 dB) between high quality analog and digital recording systems. The authors stated that the analog figures should be about 15 dB better than commonly stated to compare them with digital numbers since one can retrieve a musical signal 15 dB below the general noise level (this is somewhat analogous to the cocktail party effect, where a person can pick one conversation out of the general noise and follow it) in an analog system, while in a digital system, the lower level is no signal (digital zero) and one cannot retrieve anything below it. The same issue also pointed out that analog tape equipment can obtain a 90dB dynamic range by using dbx noise reduction. I'm not anti-digital, but I feel these items should be presented to the net. While we're on the subject of high quality recordings, the same issue of "Audio" contained a Nak ad for their new Dragon turntable. Nak is attacking a problem that no one else in the turntable business has discussed to any great length - off center records, with their consequent distortion of tonearm geometry. However, the question I'd like answered, is how does Nak's table stack up to a Linn, Mission, or Sota??? Bill Mitchell Central Services Organization Whippany, NJ (whuxk!wjm)
jj@rabbit.UUCP (01/04/84)
A comment about Doug Sax and Lincoln Mayorga on digital recording: Their comments (I've read them in Stereophile and Audio) seem to demonstrate that they do not understand some facets of digital recording. For instance, the comments that Bill Mitchell mentions regarding digital "zero" and analog perception of noise simply don't consider the process of "dither" at all. <I grant you that some digital recorders don't know about it either, which is unfortunate.> The sole effect of dither is to provide the same sort of BELOW "digital zero" perceptibility that is mentioned in the analog context. (This effect is easily explained by showing the spectrum of the signal in the presence of dither, or in the presence of analog noise. The TOTAL noise is greater than the signal, but the LOCAL signal to noise ratio <in frequency, perhaps in the critical band region of the signal> is near zero dB or slightly positive, which, when coupled to the time averaging effects of the perceptual system, provides a signal that is quite perceptable. <Ham C-W operators may have experienced this effect. :-) > ) -- -Diogenes stopped here- (allegra,harpo,ulysses)!rabbit!jj
wjm@whuxk.UUCP (MITCHELL) (01/04/84)
rabbit!jj's comments about dither being a way to improve signal-to-noise ratios are quite true - there have been some interesting articles in the "IEEE Communications Magazine" and "IEEE Transactions on Communications" about it, mostly with an eye to military applications. Unfortunately, most digital recorder designs, like rabbit!jj mentions, don't use it. The real question here is, how much improvement can dither provide (my guess from what I've read about it is several dB, does anyone have a more exact answer?) Bill Mitchell, CSO, Whippany, NJ (whuxk!wjm)
burris@ihopa.UUCP (David Burris) (01/04/84)
The Sheffield Lab engineers sent a letter to Mix magazine which was posted in the letters column. I think it was in the October issue. The were lambasting the entire digital process as the worst thing that ever happened to professional recording. From the tone of their letter it is fairly obvious there is a degree of "sour grapes" envolved. Why would a analog mastering lab specializing in "audiophile" half-speed and direct-to-disk masters be biased in their opinion of the digital process? Couldn't be because they hear footsteps, could it? There is a lot of "hocus-pocus" and "handwaving" behind the magical process of operating a mastering lathe! Most mastering engineers consider it an art to manipulate the lathe to get what they feel is a good master. Also, many "audiophiles" would shudder if they realized the mastering process used by some of the most famous mastering engineers who are recognized for their "art". The complaints of phase distortion, etc. added by using equalization at home to achieve a flat frequency response to compensate for room anomalies are dwarfed in comparison. The amount of filtering, equalization, etc. added in the mastering process are phenominal and subjective opinion at best (even if it is based on experience). One should always keep things in perspective when reading such letters. Even the Sheffield Lab's engineers stated that their opinion is not totally without bias. -- Dave Burris ..!ihnp4!ihopa!burris AT&T Bell Labs, Naperville, Il.
spoo@utcsrgv.UUCP (Suk Lee) (01/05/84)
As has already been pointed out, Sax and Mayorga were touting the "below noise" performance of analog systems versus the "below zero" performance of digital systems, but without considering *DITHERED* digital system. I hope everybody out there on the net realizes that with dither, digital systems can recover information below zero. The function of dither is to remove the correlation between the signal and the quantization noise. The resulting quantization noise looks like uniform white noise. Another point to consider is the nasty modulation noise encountered in analog recording: it too is correlated noise as is quantization noise. Second to last comment: Sax commented on the "Phase shift on the high end is unprecendentedly large compared to analog tape recording." True, but it is a smooth phase shift, there are phase anomalies all over recording systems, and (here we go) at high frequencies, phase shift simply is not significant. At high frequencies there is absolutely no mechanism for detecting phase shifts within the auditory system. At lower frequencies (those with wavelengths larger than approx. the size of your head), phase shift becomes important, but certainly not at 10 kHz. One final comment: At the expense of seeming cynical, I would point out that certain people in the music industry have a high investment in analog systems, and are less than impartial when debating the subject. I think the worst example of this is the stance Ivor Tiefenbrun is taking (Linn Products). His rabid anti-digital ravings show that someone who has been "in the field" for some time will not be necessarily more well informed than anyone else. From the pooped paws of: Suk Lee ..!(decvax,linus,allegra)!utzoo!utcsrgv!spoo No nasty letters!
gregr@tekig1.UUCP (Greg Rogers) (01/06/84)
I always enjoy and respect Bill Mitchell's comments in this newsgroup and he has invited dialog on Doug Sax's (Sheffield Lab's) interview in the January Audio so here goes. Seem's I'm always defending digital recording (CD) in this newsgroup and since I'm about to claim Sax is very biased I should first explain my bias's. 1. I should be biased in favor of analog recording since I own a state-of-the-art analog (reel-to-reel) recorder as well as a DBX noise reduction system. I now consider it obsolete and don't look forward to the cost of a digital recorder replacement. 2. I virtually can't stand listening to conventional records now and the replacement cost of CD's adds up fast. In summary I would be financially much better off to badmouth digital and stay with a very fine analog system. Unfortunately this is also true of Sheffield Lab. When CD's take over it would seem that Sax has much to lose. For the record I think Sheffield Labs should be congratulated for their fine work over the years, in fact I believe the entire "audiophile" record industry is a direct result of their efforts in the early 70's in producing the landmark S9 and S10 direct to disk recordings. To my ears the improvement offered by these disks were primarily due to reduced limiting prior to the head cutter and better disk pressing quality resulting in lower surface noise and less pop and tick defects. This simply translates to higher dynamic range of the audio signal and somewhat less background noise. The lower background noise was necessary because the overall level on the disk had to be reduced to keep from overloading the headcutting equipment on the non- limited peaks. Even with all that the surface noise was always present and detracted from quiet passages. Aside from the much more natural dynamic range on their disks I didn't find them (subjective opinion) to be as accurate in other sonic qualities as other well made recordings. As other audiophile recordings became available I found them to be generally superior to the later Sheffield recordings particularly when the Telarc digital series appeared. I have made these subjective comments about the "sound" of Sheffield disks because of the many comments in the article in which Sax implies that his records are superior due to the use of TUBE amplifiers and TUBE microphone /preamp systems. In fact he makes completely unsubstantiated claims like, "...old tube microphones are the most revered in the industry by all the recording engineers." Really? Who else uses them today? He gives no examples. Again about the mikes, "They're designed by my brother. They're literally for what they do, state of the art." I leave it to someone else to explain the last sentence. Another absurd statement, "...the only broad-gauge improvement in audio, I feel, over something made 15 years ago, is the improvement of the modern phono cartridge." I would be most interested to know what 15 year old speaker Sax uses to monitor his recordings. Anyway my point here is that this is not the type person that will readily accept new technology and I personally don't think the sound of his recordings justify his use of "old" technology. His additional comments in which he claims digital recording loses "low level information in great quantities" and "I don't have a good time with digital" seem like pretty lame complaints to me. He never gives any example of why he doesn't have a good time with digital only that "what I want to hear is somehow obscured". He never explains what is obscured or how. I suspect what he misses is the background noise. In a much more detailed and descriptive article in the December Audio, Richard Burwen gives his thoughts on digital recording. Again like Sax and myself his bias is toward analog recording. Burwen designs and manufactures noise reduction equipment for analog tape recording. Hence his product becomes obsolete with digital recording. However his conclusions on digital recording are about like mine. "Having heard about loss of ambience, harmonic distorsion at low signal levels, and ringing caused by anti-aliasing filters, I listened carefully .... The only difference I could hear between the input and the output was a little noise." Another very inteesting comment which I believe explains a lot, "Making simultaneous analog and digital live recordings, I was at first distressed to find that the digital recordings, although very clear, had lost the excitement of the analog tapes. The problem wasn't in the digital recorder (which accurately reproduced what the microphones fed in) but in the analog system's imperfections which, to me, enhanced the music." He goes on to explain that even though his analog recorders have been modified for near perfect response the small variations in response that remained affected the tone quality and dynamics. He goes on to explain tests which were done that refute Sax's comments about low level information loss. He summarizes "The main reason digital recording does not sound the same as analog is imperfection in the analog recording system." This from a man that makes his living selling noise reduction devices for analog recorders. This is very interesting article and highly recommended. Burwen also argues that the 96 db S/N ratio of digital isn't high enough but that's the only fault he can find with digital recording. Sorry this is getting a little long but Bill also mentioned the dynamic range issue so I can't quit yet. Yes, with dBx S/N ratios of 90 db is possible (or 110 db with Burwen's system) but remember all these devices have side effects which include both expansion of the frequency response variations of the analog recorder as well as breathing effects. Again Burwen honestly alludes to these problems in his article. (Yes dBx breathes, its a direct result of the design not misadjusted units. Let's not start that discussion again.) So you can duplicate the S/N ratio of digital on an analog dBx disk with side effects, or an analog TAPE RECORDER again with side effects, but you can't get around the 60 dB or so S/N of a conventional record without a dBx type compander. So no matter what you try to do the breathing and frequency variations will show up on the conventional disk. Sheffield disks, not dBx encoded simply are stuck with the 60 dB or so S/N. (Only a rare pressing is this good and they detriorate fast with age whether you play them or not.) So Sax's 15 dB that can be heard even in the presence of noise is possible but who wants to listen to it. Yes if the problem is speech recognition, like the cocktail party, or spying on the Russians, this is acceptable performance. I have no interest in listening to music however buried in the grundge of record groove noise 15 dB louder than the music. That ain't HI-FI. Greg Rogers Tektronix
pmr@drufl.UUCP (Rastocny) (01/09/84)
Burwen's system is a joke. He uses tens of Phase Linear 400s to drive very high efficiency old technology horn drivers. Burwen, on the other hand, is in his 50s. His hearing limit is probably at the 10KHz neighborhood and he can't hear the regions we are discussing. (Remember, the ear's response rolls off at an extremely sharp rate above upper hearing limits.) Phil Rastocny ..!drufl!pmr
rzdz@fluke.UUCP (Rick Chinn) (01/11/84)
re: High Quality Recordings
Recently, Greg Rogers submitted the following:
I have made these subjective comments about the "sound" of Sheffield
disks because of the many comments in the article in which Sax
implies that his records are superior due to the use of TUBE
amplifiers and TUBE microphone /preamp systems. In fact he makes
completely unsubstantiated claims like,
"...old tube microphones are the most revered in the industry
by all the recording engineers."
Really? Who else uses them today? He gives no examples. Again
about the mikes, ...
Yes Greg, there is a santa claus. I hate to differ. but with most recording
engineers, an old tube condenser microphone will bring tears to their eyes,
or some sort of highly emotional response. Most claim that the tube mics
sound warmer, particularly near overload. Some of the reasons that
abound:
more punch, particularly when it gets loud
warmer sound
i like it
tubes overload in a more audibly pleasing manner
Who uses them? Just about every contemporary studio that attempts to keep up
with the state of the art. It looks good on their rate card when they can
say that they have a couple of U67's, or M49B's or maybe a bevy of U47's. Or
how about an AKG C-12 or C22 or whatever...get the picture.
If these old antique microphones wern't revered by studio engineers, then
why are they selling for 8 to ten times what they were worth when they could
be purchased off the shelf? (a Neumann U47 microphone fetches anywhere from
1500 to 2000 dollars now. They were $250 20 years ago.) For that matter, I
have seen "wanted" ads for the VF14 tube used in the U47 that mentioned
prices of a half-kilobuck or more! (Wish I had a few.)
Put that in your pipe and smoke it!
As always, civilized discussion is welcome, but kindly direct your flames at
/dev/null.
Rick Chinn
John Fluke Mfg. Co MS 232E
PO Box C9090 Everett WA 98043
{uw-beaver,decvax!microsof,ucbvax!lbl-csam,allegra,ssc-vax}!fluke!rzdz
(206) 356-5232rmd@hpcnoa.UUCP (01/12/84)
#R:whuxk:-35500:hpcnoa:30200011:000:537 hpcnoa!rmd Jan 7 13:40:00 1984 I have an all-digital CD with a clearly audible power line hum recorded well below the noise level. The apparent volume of this hum waivers a little now and then in what sounds like discrete steps -- implying that 2 to 4 bits of information are present in this hum signal. Why is the noise apparently so much louder than this hum if the hum represents 2 to 4 bits of information? Also, why are the gaps between tracks on some all-digital CDs significantly quieter than the hiss during the music? Rick Dow hpfcla!rmd
pmr@drufl.UUCP (Rastocny) (01/16/84)
Do you like the way Sheffield's sound? Do you think SL does a better or worse job than say RCA, DG, or Philips? Just curious. Phil