dsj@rabbit.UUCP (David S. Johnson @ ) (10/02/84)
Here are some comments on Tony Lauck's CD versus LP test on the Sheffield "West of Oz" recording: (1) First note that the LP is a direct-to-disc recording, so there was no analog master tape to degrade the sound. In the September AUDIO, Bert Whyte (himself the recording engineer on some direct-to-disc sessions) performed the same comparison, both for this recording, and for the previous McBroom recording ("Growing up in Hollywood Town"). The "West" CD was made from a digital mastertape (recorded from the same feed that made the direct-to-disc master), whereas the "Growing up" CD was made from an analog mastertape. Whyte thought the "Growing up" CD was deficient compared to the LP, whereas the "West" CD was indistinguishable. He was listening to the LP using high-end equipment. One might be able to conclude from this that digital CD's are at least CLOSER to the "realism" of direct-to-disc than are analog mastertapes. (2) I wonder if Tony took care in matching volumes when doing his test. This is especially difficult when the test is performed, as he says, by first listening to the CD all the way through and then putting on the LP. Making the problem more difficult is the fact that the CD is recorded at an exceedingly low volume level (presumable to leave room for the transients, but I think Sheffield was far to conservative). In order to play it at a reasonable level, I must set my volume control at a level FAR above that at which my other CD's blow me out of the room. (Indeed, at this level the REVOX player's calibration tone representing its maximum output would require 1000's of watts to reproduce, although there is no evidence of clipping on the CD and the transients sound great.) The CD sounds "strikingly better" when played at this volume (room ambience suddenly becomes audible, etc.), and this could account for the difference Tony heard. I would ask Tony to repeat the test, carefully matching volumes and switching back and forth between the two sources (a double-blind experiment would be nice, but I'll settle for this). If there is a difference, what precisely is it? (I'm not going to buy the direct-to-disc version and make the comparison myself, as the record itself is a disappointment that no amount of sonic realism can redeem. It's something like late 60's Judy Collins - McBroom emphasizes the similarity by closing with a song from "Who knows where the time goes" - but the singing and song selection aren't as good, and the arrangements are quite pedestrian.) David S. Johnson, AT&T Bell Laboratories
lauck@bergil.DEC (10/09/84)
<> >(1) First note that the LP is a direct-to-disc recording, so there was >no analog master tape to degrade the sound. In the September AUDIO, >Bert Whyte (himself the recording engineer on some direct-to-disc >sessions) performed the same comparison, both for this recording, >and for the previous McBroom recording ("Growing up in Hollywood Town"). >The "West" CD was made from a digital mastertape (recorded from the >same feed that made the direct-to-disc master), whereas the "Growing up" >Whyte thought the "Growing up" >CD was deficient compared to the LP, whereas the "West" CD was >indistinguishable. He was listening to the LP using high-end equipment. I'm really surprised that Bert Whyte had difficulty distinguishing the LP from the CD. The difference is so great that there is no need to do double blind testing. You hear the difference and KNOW it's there. In fact, I was shocked at the extent of the difference. I'll have to get a copy of the September Audio and read the article. I'm curious as to the record playing equipment involved. I didn't bother to buy the CD of "Growing up", since it would prove nothing except the limitations of analog tape recorders, probably not the state of the art recorders at that. I certainly didn't feel the need to buy the CD lest the analog disk wear out.... >(2) I wonder if Tony took care in matching volumes when doing his test. >This is especially difficult when the test is performed, as he says, >by first listening to the CD all the way through and then putting on >the LP. I took no care in matching the levels, I just played the music. The tonal balance was so different that the concept of level matching makes no sense. At what frequency do you match levels? If measuring power, on which portions of the program material? After the inital test I then played various cuts, one cut at a time, and listened at all combinations of CD or LP louder, or as close as possible by ear. In each case, the LP sounded better, even when it was much too soft or much too loud for my taste and the CD was set "properly". I then called up my pro digital friend, E. Brad Meyer, who is an audio writer and recordist. I told him that he was going to have to "reconvert me" back into the pro-digital fold. He suggested that perhaps Sheffield should have made their CDs by playing a pressing of one of their direct disk records into a digital recorder. I thought he was joking. Little did I know... The prescribed treatment was to borrow a SONY PCM 710 and an ABX double blind comparator box. I had to swear to level match within .1db. I assured him that I had a tone generator and a suitable meter. My initial tests consisted of just listening through the PCM and comparing it to the Sheffield recordings and other audiophile recordings, including the Performance Recordings Prokofiev 6th sonata and the Reference Recording Symphonie Fantastic. It was immediately clear that any PCM degradation was minimal, subjectively at least an order of magnitude less than the difference between the "West of OZ" CD and LP. There was no question that the LP and the LP via the PCM both sounded vastly better than the CD. Perhaps my friend Brad had been serious in his recutting suggestion. I then level matched the PCM to within .05 db on each stereo channel. To those who haven't done it before, it is a real pain, unless you have ten turn pots and fancy meters. It took me two hours, and caused me nearly as much pain as when I measured the mass of an electron in college physics. (My degree was in mathematics.) The resulting level setting put the PCM in a poor position, since without an attenuator on the output I couldn't get a level match with a recording level above -24db. This meant I was running effectively at 13 bits. When the stylus was lifted, the PCM noise (dither) was clearly audible, making identification of the PCM immediate. However, this noise was not detectable when a record was playing since it was far enough below the record noise of all the records I played. The final result: I correctly identified the PCM in 24 out of 42 trials, which is not statistically significant. Subjectively, I felt that any differences were at the very limit of my perception. Perhaps I could keep up this performance every night for several months and reach statistic significance, but why? It became clear to me that the problem with bad sounding CDs is not in the system itself, since the CDs sound much worse than the LPs via PCM. (The 710 uses the same encoding format as CD's.) The obvious explaination, one argued publically by many, is that recording engineers and record producers haven't learned to use the new, more accurate digital medium. I don't buy this. The technology has been available for five years. By now these problems should have been overcome. What's going on here? I hooked the PCM710 up to my video recorder and made some live recordings of my wife's Steinway piano and my son's 12 string guitar, using a pair of AGC C451 cardiod condenser microphones. The result: the piano sounded much like CD piano recordings, not too bad. The guitar suffered from moderately severe "digitalis". Do I need new microphones? Here's a subject to ponder: why do digitally mastered LPs sound bad when digitally copied analog LPs sound good? Why should analog then digital sound good while digital then analog sound bad? Is it a system interaction problem? Is it a psychoacoustic problem? Tony Lauck ...decvax!decwrl!rhea!bergil!lauck
rzdz@fluke.UUCP (10/11/84)
> I hooked the PCM710 up to my video recorder and made some live > recordings of my wife's Steinway piano and my son's 12 string > guitar, using a pair of AGC C451 cardiod condenser microphones. > The result: the piano sounded much like CD piano recordings, not > too bad. The guitar suffered from moderately severe "digitalis". > Do I need new microphones? I think that you ought to try some different microphones. The C451's have a tipped response curve (check the curve that AKG includes with them). Their response is very *level*, but there is perhaps a 4 dB rise between 20 and 20khz. You can hear it in them, as they tend to sound *very* bright. They're *very* good microphones, they just sound bigger (brighter?) than life. As a recording engineer, I like to use the 451 for acoustic guitar, and on mushy piano's (not your Steinway, I hope). The brightness helps emphasis the attack of the guitar, and gives the piano a brightness that is hard to obtain with an equalizer. On the negative side, this excess brightness might be part of what you call "digitalis". I suggest that you try a pair of the new B&K recording microphones (4004, 4006 i think) or the Neumann KM84 or KM83. The 84 is quite flat, and doesn't have the tipped response that the 451 does. They have a very neutral sound, sometimes almost warm. The 83 (omni) has an on-axis rise in its response. You can play with its positioning to use this rise to advantage, or run the mic at 90 degrees incidence to make it flat. Rick Chinn John Fluke Mfg. Co MS 232E PO Box C9090 Everett WA 98206 ihnp4!uw-beaver----\ decvax!microsof \ ucbvax!lbl-csam \ +====!fluke!rzdz sun / sb1!allegra / ssc-vax------------/ (206) 356-5232
rmd@hpfcla.UUCP (rmd) (10/12/84)
The tests which Tony Lauck ran Using a Sony PCM adapter to record Sheffield LP's were very interesting to me. This is something I had always wanted to do myself to rebut anti-digital arguments. Being pro-digital, I am not surprised at his results which indicated that a digital recording of an LP sounds very much like the LP. Tony was still bothered by the fact the LPs do sound different and he couldn't understand why Bert White in Audio didn't hear the same differences he did. I believe that these things are largely explained by some fairly obvious and common attributes analog systems. First, it is the nature of digital processes to be repeatable in the common objective measures of frequency response, speed accuracy, distortion, etc. Some people argue that digital systems vary subjectively and that may or may not be true. However, no one that I know of questions the consistency of frequency response, etc. On the other hand, it is the nature of analog systems NOT to be repeatable. It would be possible to acheive greater repeatability by spending more money in the design and manufacture of equipment, but most "high-end" manufacturers design for subjective rather than objective performance. There are in fact large (relative to digital) variations in the objective performance of turntable/arm/cartridge/head-amp/preamp combinations. There are also large variations in the equipment used to record and cut LP's. Frequency response variations can easily exceed 5db when 1db is clearly detectable. Longterm playback speed can vary over a 1-2% range. While many would claim that these variances are not important, they are certainly important for CD-LP comparisons. As far as I can tell, most CD-LP comparisons are done with no good data about the objective performance of the analog chain involved. Without such data, there is no reason to assume that differences are due to any reasons other than the obvious ones. Rick Dow hpfcla!rmd
bytebug@pertec.UUCP (roger long) (10/14/84)
One thing to ponder is just what are we using as a reference point? If we compare a CD to an LP in a test such as this, and they sound different, we are supposed to immediately come to the conclusion that the LP sounds "right", and the CD is "wrong?" I've listened to the "West of Oz" CD on my system, and thought it sounded just fine. On the other hand, we all heard what the "official" Sheffield line on digital was before they brought out their line of CDs. Perhaps they've mixed them to sound different than their LPs just to fuel the anti-CD arguments? I no longer own a turntable, so perhaps I am biased. But if anyone wants to bring Ms. McBroom over to my place, I'd be glad to participate in a double-blind test of CD vs. the real thing. :-) To make any other sort of comparison is like comparing apples and oranges. -- roger long pertec computer corp {ucbvax!unisoft | scgvaxd | trwrb | felix}!pertec!bytebug
muller@inmet.UUCP (10/16/84)
*** Nice experiment, trying the blind comparison. A few comments, questions, and suggestions: (1) You say analog to digital sounds good, but digital to analog sounds bad. Then you ask why. Umm...seems to me that this is a bit of a generalization. As I try to answer this to myself, and as I ponder the results of your PCM test, I find lots of room for any specimen to be poorly done, but no reason to explain why A to D is ALWAYS better than D to A. (2) With regards your piano and guitar recordings, why not try the same setup, recording the same stuff into a GOOD analog tape machine? THEN do a comparison of the two recordings PCM -> VCR vs. Analog tape. You will probably hear some differences, but the audible features you describe as characteristic of digital may be present to some extent in your analog recording. What might they be? Well, maybe what you heard is exactly what your mics heard. A look at most mics' spec sheets shows definitely non-flat frequency response. They were designed (evolved?) to sound good, not necessarily have flat-looking response. Perhaps they compensate for other features of the recording medium, features which digital systems don't quite duplicate? (Can we assume there was no real loss of information in the VCR, such as lost bits that were only poorly "fixed" on playback? (I don't know much about how VCR's work.)) (3) Have you, or anyone else, dont this same PCM -> VCR test using pink noise and an analyzer? Yeah, I know, you can't really expect .5 dB precision from this, but it sounds like we are talking about more than this anyway. ... Looking objectively at your results, you have shown that the digital process itself is not really making things sound bad. So where then is the problem? It must elsewhere in the recording process, either the total composite frequency response, or the dynamic range, or non-linearities or so Thus it would be good to try the other recordings I suggested, just as another control.
lauck@bergil.DEC (10/17/84)
>I no longer own a turntable, so perhaps I am biased. But if anyone >wants to bring Ms. McBroom over to my place, I'd be glad to participate >in a double-blind test of CD vs. the real thing. :-) To make any other >sort of comparison is like comparing apples and oranges. The test should be three way, CD vs. LP vs. the real thing. To make it fair it would have to be more than blind. :-) Ms. McBroom on LP sounded more like a real singer than Ms. McBroom on CD. The differences involve qualities like air, depth, dimensionality, etc. However, the record is NOT a solo album. There are other musical instruments on the recording, e.g. clarinet. I am quite familiar with the live sound of these instruments and find their LP rendition more accurate. Incidentally, I didn't think the sound on the CD was bad at all, UNTIL I heard the LP. Perhaps you should have kept your turntable. Tony Lauck ...decvax!decwrl!rhea!bergil!lauck