Behind the Scenes (Audio magazine, Feb. 1982)

The 70th Convention of the Audio Engineering Society was held at the Waldorf Astoria in New York from October 30th through November 2nd and may well be remembered as having historic significance. Quite coincidentally, that Grande Dame of hotels, the Waldorf, was celebrating its Golden Jubilee 50th anniversary, as a huge, elaborately decorated, multi-tiered cake proclaimed from its display in the lobby.

This 70th AES Convention marked the last in the three conventions-per-year format which the AES has been following for some years now. The next AES Convention is set for Montreux, Switzerland in March 1982. Then instead of the usual May convention at the Hilton in Los Angeles, there will be a convention in October 1982 at the Disneyland convention facilities in Anaheim, California.

After that it will be another foreign venue, with the next New York convention in the fall of 1983, and not necessarily at the Waldorf.

The truly historic highlight of this AES Convention is that at long last we are about to establish standards for digital recording. At a very heavily attended meeting of the Digital Standards Cornmittee.(with AES legal counsel standing by to advise on any "sticky" points), a draft proposal was formulated which recommends 16-bit linear encoding at a sampling rate of 48 kHz per second for "fixed head" digital recorders, and a sampling rate of 44.1 kHz per second for helical-scan, slant-azimuth digital recorders. Essentially, this is the standard that eventually will be established in conjunction with such groups as ANSI. There are certain oddball cases. For example, the British Decca digital recorder uses a 1-inch helical-scan format but has always employed a 48-kHz sampling rate. In conforming to the new standards, existing digital recorders will have to be retrofitted with circuits and switches to permit selectable sampling frequencies. This must be done, because if a recorder which had an original sampling rate of 44.056 kHz (a common figure in most Japanese helical slant recorders) is used to play back a tape with a 44.1-kHz sampling rate, there will be a very slight pitch change, possibly detectable by someone with perfect pitch.

Conversely, there would have to be adjustments made for the playback of 44.056-kHz tapes on a 44.1-kHz digital recorder.

A 48-kHz sampling rate will permit a frequency bandwidth extending beyond 20 kHz. Those who would prefer an even higher top end will not be happy about all this but the next applicable multiple for sampling rate is 60 kHz which is deemed too technically difficult and too expensive in implementation.

There are other points to clear up, of course, but once the Committee's work is completed we will indeed have a digital standard! It was generally felt at the Convention that the establishment of a digital standard will stimulate a number of companies and give them the impetus to become involved in digital technology. Needless to say, there was plenty of digital activity at the AES Convention.

JVC demonstrated their PCM digital audio cassette recorder, which I described in last month's column. The system certainly is compact, comparable to the typical analog cassette deck, and the sound quality I heard from the metal-tape cassette was excellent, with no discernible wow or flutter, or distortion. Dynamic range was most impressively wide, and the music was unsullied by any tape hiss. The odd sampling rate of 33.6 kHz is said to permit a frequency response beyond 16 kHz, which some critics point out is less than is available from many analog cassette decks. However, JVC notes that this sampling rate is necessary in order to obtain one hour of recording time. They also point out that the frequency response curves of most analog cassette recorders are not nearly as flat as on the PCM unit and that the signal from an analog unit lacks the other desirable attributes available with the PCM recorder. JVC also showed their DAS Series 90 professional digital recorder, complete with digital editor and digital delay unit for disc cutting. I have been using this system with absolutely superb results. For the Smithsonian Institution, I recorded Victor Herbert's complete operetta, "Naughty Marietta." 3M showed their 32-channel and 2/4 channel digital recorders, which no doubt will soon be retrofitted for the new 48-kHz sampling rate. They demonstrated how a tenth generation digital dub is indistinguishable in sound from the original master, especially in terms of signal-to-noise ratio. This point is somewhat controversial, with some experts claiming subsequent dubs are structured differently from the original. Perhaps so, but most people certainly can't hear any difference between copies.

Sony offered new digital equipment in several areas. Under development for some time, the PCM 3324 24-channel digital recorder will be available for delivery by the time you read this report. It is a fixed-head recorder, using half-inch tape at a speed of 15 ips and providing 60 minutes of recording on a 14-inch reel Quantization is 16-bit linear encoding, and sampling rate is selectable for various frequencies up to 55 kHz. The 3324 features separate SMPTE time code generation, which allows synchronous recording of up to 72 tracks, and the SMPTE track permits compatibility with video recorders. The PCM 3324 also provides two additional analog tracks which allow conventional razor blade cut-and-splice editing. Sony emphasized that their special analog-to-dig ital and digital-to-analog converters use Sony-developed integrated circuits rather than complex discrete circuitry which requires very precise adjustments.

Sony claims their new ICs assure 16-bit accuracy without the need for adjustments and that their new Cross Interleave Code error correction system, used on the PCM 3324, is so effective that it prevents loss of the music source even if up to 88% of signal is interrupted within a constrained length of tape! The usual digital specs for dynamic range (90 dB), unmeasurable wow and flutter, etc. apply to the PCM 3324.

-------p84 Sony PCM 3324 digital recorder.

Sony also showed their PCM 1610, an updated version of their original PCM 1600 helical slant recorder. This unit also uses 16-bit linear quantization, and one assumes it too will be retrofitted with the 48-kHz sampling rate. The 1610 now has an SMPTE time-code generator which permits immediate editing on the new Sony DAE-1100 digital editor or with a video editing console. The PCM 1610 uses Sony's error correction scheme, the Cyclic Redundancy Check Code, which is said to guard against any dropout and eliminates pulse-noise or crossword error. Tapes made on the older PCM 1600 are totally compatible with this new PCM 1610, whose price has been set at $28,000. More on new digital equipment and other AES equipment next month.

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(Adapted from: Audio magazine, Feb. 1982; Bert Whyte )

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