TAKING CD IN STRIDENT
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Contrary to the expectations of many nay-sayers, the Compact Disc players and discs have been accorded an enthusiastic reception by consumers. As a consequence, both are in short supply. However, that may soon improve here: Billboard recently quoted Hans Gout, senior CD director at Polygram, as considering it an "overriding priority" that the Com pact Disc substantially penetrate the U.S. market.
Even though the software shortage is particularly acute, enough discs have come to hand to demonstrate that although there is much to admire, many of them have sonic anomalies which are very off-putting. I refer most especially to the shrill and strident sound of the first and second violins in classical recordings. In my CD re views, which first appeared last issue, I made particular note of this problem. I took pains to point out that the objectionable sound is not an inherent fault in digital recording, but rather a consequence of close multi-miking techniques and the use of microphones which many feel have an over-bright, "tizzy," high-frequency response. In the past, the bright top end of these microphones may have been attenuated by the processing loss and noise masking of analog recording. In digital recording no such losses occur, and therefore any sonic imperfections are starkly revealed.
Apparently, many of those who bought CD players and discs have discovered the problem of the strident strings and other sonic aberrations. Miraculously, the negative comments of these people seem to have reached the right ears. The following excerpts are from an article by Jim Sampson which appeared in a recent issue of Billboard: "The superior sound quality of the Compact Disc is leading to changes in recording technology, away from a dry studio acoustic and from elaborate multi-miking. That's the opinion of Dr. Andrew Holschneider, president of Deutsche Grammophon Productions.. .
"Several critics felt the digital sound of the Berlin Philharmonic in large orchestral works was 'harshly' brilliant.
And the English Concert Compact Disc of Vivaldi's 'Four Seasons' features very bright string tone and 'back ground street noise.' ". . As producer of The English Concert on DG/Archiv, Holschneider agrees that the CD medium demands new technical standards: 'It is a real challenge and we're learning. . .
"The choice of a hall has become much more critical, he says. 'It cannot have too dry an acoustic, because the CD sound is itself clearer.' And Holschneider will reconsider locations poorly isolated from the outside, such as Lon don's Kingsway Hall or Henry Wood Hall, where his 'Four Seasons' was re corded.
"The multi-microphone techniques of the 1970s might soon be replaced by the twin-mike sound of the 1950s.
Says Holschneider: "A recording technology which tries to reproduce the music as simply and naturally as possible is the best." He points to Gunther Breest's two-mike production of Verdi's 'Falstaff' under Giulini [conductor of the Los Angeles Philharmonic] as a good example." Well, Hallelujah! That certainly is a step in the right direction, although even if only two microphones are employed for a recording, the use of the offending over-bright microphone is to be avoided. Depending upon the acoustics of the recording hall, the engineers can use quite a number of two microphone configurations such as the Blumlein coincident crossed figure-of-eights or the M/S (middle-side) with a forward-facing cardioid and the lobes of a figure-of-eight mike facing left and right.
The same story in Billboard states that "perhaps the most frequently heard critical complaint so far is the marketing of analog recordings as digital audio." Indeed, the first mass produced CD from PolyGram's Hanover plant last August was Claudio Arrau's analog Philips recording of the Chopin waltzes. Nowhere in the packaging is the recording's non-digital ancestry acknowledged.
"At DG Productions, however, there s a clear policy that, for the present, all CDs will come from digital masters. Holschneider says he expects that analog-mastered repertoire will appear on the yellow label sometime in the future, but not as part of the first year's releases."
Some English critics seem particularly annoyed with the mislabeling or non-labeling of recording origin on CDs. Some Japanese CDs have been made from analog recordings. I don't think this is necessarily reprehensible if he recording is of high quality. In fact, it would be extremely stupid to ignore he riches of analog recordings in the vaults of the record companies. Consider the fact that Dolby A noise reduction, has been in general use for over 15 years. Given the various tape oxide formulations over these years and the technology of analog tape recorders, the average signal-to-noise ratio on the master recordings should be around 70 dB, and a bit higher in more recent years. If the original tape master is used-not the cutting master (which quite often has undergone various forms of signal processing, so the original sound quality may be degraded) it will transfer very nicely to a CD. With a 70 to 72 dB S/N, noise will not be totally inaudible, but it will be very quiet indeed. Imagine what this could mean:
There would be no degradation, no transfer or incremental noise, no in crease in distortion, and a wow and flutter specification equal to the original. You could get one of your favorite recordings in what would be tantamount to having the master recording itself! You would hear that favorite re cording with no ticks, snap, crackle or pops. Further, with the non-contact caress of the laser beam playback, the CD will remain in master tape condition forever! There is a veritable treasure trove of analog recordings which are great performances and sonic masterpieces. A smart, forward-looking record company will put a good classical A & R man to work, mining their vaults for out standing analog recordings suitable for transfer to digital disc. When I think of the glorious music tucked away in the vaults of EMI, Decca, Deutsche Grammophon, Philips, et al., my mouth waters!
[Editor's Note: Analog masters are, in fact, less likely to sound overly bright on CD than are digital masters made with analog mike techniques. And it might be possible to make two-hour transfers from treasured monophonic performances. -I.B.]
One thing I have noticed with various CD recordings is that, under the instructions for cleaning digital discs, each company seems to have its own idea of how this should be done. Most warn against the use of solvents such as benzene, gasoline, carbon tetrachloride, etc. Some warn against the use of any liquid. Yet others tell you to use ethyl alcohol or warm, soapy water! Most seem to agree on one point:
The discs should be cleaned from the center towards the periphery of the re cord. You say you were under the impression that CDs were impervious to dust, dirt, fingerprints, and scratches? Well, I've seen a CD actually gunked with peanut butter, then washed with a mild detergent, and it played back flawlessly. I've also seen a CD slashed with a penknife, and it also played back with nary a pop or click! In spite of this apparent immunity to such mis treatment, most companies urge, quite properly, that a CD be accorded the same care and respect as analog LPs.
Believe it or not, I have only encountered two CDs with glitches, and I followed directions to blow on the disc and wipe off the condensation with a soft cloth (not in a circular motion, but across the disc's surface from the center outwards). It worked. The glitches disappeared, and several friends who have tried it report similar success.
One absolutely cast-in-concrete piece of advice in the handling of CDs is that they must never be subjected to heat or anything else that could cause warpage. With a warped CD, the laser beam can be de-focused and render the disc unplayable.
As far as most people are concerned, digital discs are strictly a play back-only medium. Some of you may have heard vague rumors that one day there might be a recordable digital disc. Well, it is not going to show up at your friendly local hi-fi dealer any time soon, but early research has actually taken place. As you might expect, some research was undertaken by Philips in Eindhoven, Holland, as well as by 3M in the U.S. and by Panasonic's parent, Matsushita, in Japan. In very simplistic terms, the Philips technique is a thermomagnetic process on a pre-grooved disc, with a track spacing of 1.7 microns. Amorphous layers of a special alloy are vacuum-deposited on the grooves, and cutting is accomplished with a laser essentially the same as that used in the CD player.
Sufficient density and S/N ratio have been achieved to permit 30 minutes of music recorded on one side of the 12-cm disc. The same laser plays back the recording, and with only slight modification, the experimental recorder can play back normal CDs. A great idea, but where will the high-quality source material come from?
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(Adapted from: Audio magazine, Aug. 1983; Bert Whyte )
Also see:
Dr. Thomas Stockham on the Future of Digital Recording (Feb. 1980)
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