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Beacham Exhibit #5

By Andrea M. Rotondo NEW YORK-Sonic quality has come a long way since those early days of needle drop recordings. Today's engineer has the advantage of being able to produce a recording of high sonic integrity via the multitudes of professional recording gear available. Every step in the recording chain is carefully considered to insure accurate sound reproduction. New software formats however, are not as interested in accurate sonic replication as many engineers would hope.

Owner/chief engineer Jim Berry, of HBR Audio in Lowell, MA, said, "We are being bombarded with formats and none of them particularly improve the quality of the finished product." Berry went on to say that studio recordings are currently reaching technical and creative heights never before imagined. "The designers of new formats are doing the engineers and the consumer a disservice by not designing high sonic quality into their standards," Berry noted. "The new DCC and Mini-Disc aren't bad formats but they do not raise the quality of duplicated products either."

All of this talk of new formats, namely the DCC and the Mini-Disc, have left many engineers wondering if the quality of their work will be carried over to the software version of the consumer's choice. After all the advances in professional audio, will the consumer market support formats which actually detract from the original quality of a recording? Engineers are feeling as if they are taking one step forward and two steps back with the introduction of DCC and MD.

Both the DCC and the MD employ data compression which according to Van Webster, president of Webster Communications in Los Angeles, "makes a lot of assumptions."

Data compression also solves a major beadache for the record labels. They are able to support a recordable CD format while banishing fears that the product would be of equal quality to a master recording. Data compression works in conjunction with the threshold of human hearing. It sets a threshold frequency of what it believes the ear can and cannot hear. If audio signa. is present which is deemed inaudible, then it is not recorded. This transiates into a narrow bandwidth.

Others state that data reduction technology is such that these techniques can be used without creating inferiority. According to Ken Pohlmann, coordinator of the Sound Recording program at the University of Miami, "Given today's technology, if you want to be able to record and erase 74 minutes on a disc that's as small as the MD or tape that's as cheap to manufacture as the DCC, something has to give. The only choice is to reduce the amount of data being stored. Data compression technology is quite sophisticated and I think for many, many applications people will be unable to tell the difference between the CD and the two other formats.”

A seminar entitled Low Bit-Rate Audio Coding will discuss this type of technology during the AES Convention, October 6 at 7 PM. Pohlmann will be hosting the seminar. The panel will include author John Eargle; Louis Fielder, Dolby Labs; Bart Lacanthi, BNL Research; Stephen Smyth, Audio Processing Technology; John Stautner, Aware and Raymond Veldhuis, Philips Research.

The DCC format boasts that it is compatible with analog cassettes. The compatibility is a one-way street, bowever. The DCC player will play back existing analog tapes but analog decks will not play back DCC tapes.

All of this could spell trouble for both the professional recording engineer's psyche and the consumer's value-perdollar ratio. However, Webster believes that sound quality will be a minor issue in the consumer market. "The consumer has never made their decisions in the marketplace based on audio quality," remarked Webster. "They have always made their decisions based on convenience and cost." Berry agreed that the consumer rates portability over performance. "People chose the cassette over the LP because of the format's portability."

According to Webster, neither format will find its way into the professional market. While a recordable CD would be welcome in studios the world over, the Mini-Disc just isn't up to snuff. Webster said, "The MD will not win over the pro market in its present form. The pro market needs a broader bandwidth disc-based system."

Howard Johnston, owner/chief engi

neer at Different Fur Recording in San Francisco, concurred. "I think the Sony MD will be successful as a format that you carry around with you," said Johnston. "I don't think that either the DCC or MD will take the place of the compact disc, however, or enter the pro market because the specs of these products are less than those of the CD." Johnston went on to say that the MD has the advantage of its small size, recordability and random access. "It doesn't have the negative aspects of tape moving across tape heads which presents problems," concluded Johnston.

At White Crow Audio in Burlington, VT, owner/chief engineer Todd Lockwood is looking forward to makin sound quality comparisons between DCC and the MD. Although he bel.. that the DCC holds more prom the format of choice for the consumer he wondered if the quality of the product is at a high enough level. Lockwood used the example of DAT to prove his point. "DAT is a good format but it is not a particularly good solution to the needs of the professional," said Lockwood. "There was no reason why the DAT cassette had to be so tiny. Making the tape twice as wide would have probably reduced the error rate quite a bit."

PPO SOUND NEWS

N

MD

o, it doesn't stand for Medical Doctor. It doesn't stand for Mogen David, or even Mad Dog. It stands for Mini Disc. One look at Fig. 1 explains the name. The Mini Disc is a 2.5-inch optical disc format. It stores 74 minutes of stereo digital audio with a frequency response of 5 Hz to 20 kHz, a dynamic range of 105 dB, and a sampling frequency of 44.1 kHz. Data is encoded with EFM, and error-protected by CIRC. But MD is not CD-compauble. It employs data compression. And it is completely recordable and erasable.

The Mini Disc is the latest brainchild of Sony and is clearly targeted at the analog cassette market, as well as any new formats with similar targets, specifically the Philips DCC digital cassette format. The MD is a consumer product that has the potential of redefining the economics of music retailing, and takes us all one step closer to the day when tape sheds its mortal coil and goes to that great head gap in the sky.

MD attempts to snatch the Holy Grail of audio media: high sound qual-ity, random access, durability, portability, convenience, shock resistance and recordability. Cassette tape comes close, but ultimately fails, especially in terms of sound quality and random access. The CD fares well in these criteria, but is not as portable as one would like and is not recordable. MD proposes to merge analog cassette tape (emphasizing the portability of a Walkman-type concept) and compact disc, resulting in a high-fidelity, portable, recordable medium.

The MD system employs two kinds of media: magneto-optical media for recordable blank discs and CD-type optical media for prerecorded software. The magneto-optical drive (MOD) technology in MD is similar to others already in use, but brings some clever ideas to the party. For example, it allows overwriting, whereby previously recorded data can be erased and new data written simultaneously. As with

other MOD systems, a magnetic head is positioned over the laser source and on the opposite side of the disc. To record, the laser heats the magnetic surface beyond its Curie point at 400° F so that the polarity of the heated magnetic spot is directed by the bathing magnetic field. As the disc rotates, the heated spot moves away and cools, and the magnetic information is stored. The size of the recorded spot is determined by the reversal cycle of the modulating magnetic field, as opposed to methods in which the laser is turned on and off. Because the laser source is always on, the controlling circuitry is simplified.

The MOD disc is built on a polycar bonate substratum, with a terbium ferrite cobalt recording layer covered by a reflectve aluminum layer and top protective layer. The terbium ferrite cobalt recording layer changes polarity with 80 Oersteds-about one-third the coercivity of other MOD media, this is important because the magnetic head does not touch the media, and the need for stronger fields at the recording layer would necessitate higher heat generation and power consumption. The magnetic head itself is said to be particularly power-efficient, and able to perform polarity reversals at a rate of 100 nanoseconds per cycle.

The dual-function, 0.5 milliwatt laser can operate with both recordable and read-only MD media. Its design is essentially taken from a conventional CD pickup, with the addition of a MOD analyzer. When using a MOD disc, the pickup distinguishes the polarization angle of the reflected light, which is determined by the magnetization of the recording layer. The MOD analyzer converts the polarization angle intò a light intensity, and light is directed to two photodiodes; these signals are subtracted to generate a positive or negative readout signal. When playing back a CD-type disc, the pickup reads the intensity of the reflected beam as

66-469-93 - 9

Beacham Exhibit #7

ust when you thought the familiar silvery compact disc was all you needed in terms of audio, along comes yet another incompatible recorded music format. The latest format, Sony's take-along Mini Disc music system, combines features of CDs and Walkman-type portable cassette machines. Both the Mini Discs and another new format scheduled to appear next year, digital compact cassettes, bring the advantages and disadvantages of computer technology to music recording and playback. The growing variety of audio hardware promises a confusing battle for market domination.

Miniaturization has been the key goal in designing the Mini Dise system. If Sony engineers succeed in cramming all the components into the mock-ups shown recently, you will have a choice of two exceptionally compact machines: a recorder about the size of today's portable cassette recorders or a tiny playback-only machine that fits into your shirt pocket with room to spare. In addition to extreme compactness, the machines give you one-second access to any music selection on the 2.5-inch discs, plus the advantages of digital audio technology compared with standard cassettes (see A Growing Menu of Incompatible Audio).

The development of prerecorded and erasable Mini Discs involves the refinement of four technologies:

•Digital-audio compression that uses five times less data than standard compact discs for 74 minutes of audio-with some loss of music fidelity.

⚫A technique for erasing and recording Mini Discs at the same time, using magnetism and laser heating.

A small laser that helps erase and record discs, or illuminates both prerecorded and erasable discs for playback.

A memory feature that enables you to handle the machines roughly-even jog with them-without causing audible interruptions.

If Sony markets its Mini Disc system next year as scheduled, it will be a first for most of these technologies in audio products. Except for the memory feature, however, similar technologies have already appeared in other prototype disc recorders not yet sold (see Erasable Discs Revisited). The new Mini Discs are mounted in plastic cases with metal shutters, much like 3.5-inch diskettes used in personal computers. This protects the discs and makes them easier to handle, an important advantage for a portable audio system. To achieve their goal of storing the same amount of music -74 minutes on Mini Discs as conventional compact discs, Sony engineers had several options. "One possibility," said Katsuaku Tsurushima, "was to develop some completely new recording mechanism. But another option was to use digital technology to manipulate and compress electronic signals." Sony settled on a compression scheme that takes advantage of two particular limitations of human hearing the threshold of hearing, referring to the decibel level below which humans can no longer detect sound vibrations; and the masking effect that occurs when loud and soft sounds with similar frequencies strike the ears simultaneously and the soft sound isn't recognized.

Dunng Mini Disc recording, the incoming analog signal is sampled and digitized much like it is in existing CD technology. But then the compression encoder analyzes the data and selects only those digital signals representing sounds the human ear is likely to hear. Address information, which helps the laser find its place on the disc when there's an interruption, and error correction data are added and the digital signals are recorded onto the disc.

Sony's compression scheme squeezes the same amount of data into one-fifth the space of conventional digital recordings with only a slight loss in sound quality after it's decompressed, the company claims. Demonstrations of Mini Disc audio have so far been too restrictive to allow for compar isons with other audio media. However, one Sony engineer 6448 SCIENCE 4.GUST 1991