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Digital audio is shaping the future of hi-fi but how will the new technologies affect video movie making?



The days when sounds and pictures are represented by gently undulating waveforms are rapidly coming to an end; in the digital age information is recorded, and stored as streams of numerical data, and sooner, rather than later, that will  include domestic camcorders. In some quarters it already does, Sony pioneered the use of digital PCM (pulse code modulation) audio recording systems on the Betamax F1 portable outfit back in the mid 1980's, and their PRO series camcorders have featured PCM sound for the past four years.


Digital sound has had a dramatic effect on domestic hi-fi, Compact Disc is now the prime carrier of music in the home, and sales of vinyl records  have been falling like a stone for the past three years, even the good old compact cassette is nearing the end of the line. When you look back over the history of recorded sound it seems that on average domestic audio formats have a 20 to 25 year life cycle. Depending upon your point of view the worlds consumer electronics manufacturers either recognise or engineer this trend, and somehow always seem to have a replacement  ready and waiting, There are currently two contenders poised to take over from compact cassette, actually there were three but digital audio tape (DAT) which uses a rotary head recording system, very similar to video in fact, was launched in 1988 and peaked a little too early. It suffered by being too complex and expensive but it hasn't disappeared altogether, though,  and has since found a niche for itself in professional and broadcast audio.


The battle is now on for the compact cassette mantle; in the red corner we have Sony's optical Mini Disc or MD, in the blue corner is the tape-based Digital Compact Cassette or DCC, developed by Philips. Both systems offer broadly the same kind of recording and playback facilities, and, from a consumer standpoint, sound pretty good, comparing favourably with Compact Disc. DCC's main advantage is that the new generation of decks will be backwards compatible and can play analogue compact cassettes. MD has immense gadget appeal plus CD-like immediacy and rapid track access. Early sales figures suggest that MD has taken an early lead but both systems face a long haul, and in the end it will probably be the range and availability of software that will decide the issue.


So does this have any relevance to video movie-making? Yes, is the simpler answer, both DCC and Mini Disc used sophisticated psychoacoustic (try saying that with a mouth full of toffees...) data compression techniques to cram a lot of information into a relatively small space. They reduce the amount of data going onto the disc or tape by discarding sounds that the engineers at Sony and Philips have decided we either cannot hear, or would naturally ignore as they're masked by other, louder sounds. PASC (precision adaptive sub-coding) on DCC and ATRAC (adaptive transform acoustic coding) on MD both have promising futures in other forms of digital sound recording and you can bet your bottom dollar, or yen, that son of PASC or ATRAC will turn up on a camcorder near you pretty soon.


Of more immediate interest is what DCC and MD can do for you right now. Of the two systems MD has the greatest potential for video movie-makers, not for any technological reasons but simply because the first DCC machines are all mains-powered audio components. Sony took the view that a portable Walkman-style player/recorder would be more attractive, and judging by its early lead they may well be right. We've managed to acquire one of  a Sony MZ1 MD machine, to see what it can do, and we've also been lucky enough to get hold of one of the first ECM-727 microphones in the country, it's brand new and has been specially designed for this kind of digital media. They're not cheap, the MZ1 costs 500 , and the mic a further 100 , but if you cast your mind back ten years you may recall that the first Sony Walkman personal stereos cost over 100, heaven knows what that would be in today's money!


From the point of view of video movie-making one of the most potentially useful features of this kind of system is speed accuracy. Camcorder transport systems are already very stable, with wow and flutter both less than  0.1%, if  audio systems like DCC and MD can match that they could, in theory have a useful role to play in recording and dubbing soundtracks, something most analogue cassette decks  have never been very good at because of their relatively crude tape transport systems.



To find out we made a series of test recordings using a Panasonic NV-S20 and Sony TR camcorder, with the MZ1 and ECM-727 along to capture the sound for later comparison. The recording were all made at the same time, under identical conditions with all three machines suffering the same kind of physical treatment. We'll get to how they fared in a moment, but first a few words on what else the MZ1 can do.


It's a little larger and heavier than a normal Walkman, but it will still fit comfortably into a coat pocket. The discs are loaded in a slot on the front, and as soon as you push one in the motorised loading mechanism whips it from your hand. Once inside the machine sets about telling you what's on the disc by reading the TOC or table of contents, this is shown on an LCD panel on the top of the machine. If it's a pre-recorded disc it will tell you the number of tracks, title and running time. From then on it's pretty much like any other CD player; press play and you'll hear the whole disc from start to finish, or you can program in your own track selection. Track access is very fast, taking no longer than three or four seconds to scan across up to 70 minutes worth of music. As each disc plays the track title is shown in the display window, along with track number and duration in minutes and seconds.


The MZ1 comes with it's own set of in-ear phones, but after having tried the excellent new MDR-D55 headphones, which are an optional extra, we gave the standard items a miss. Power comes from a 6 volt nicad pack, it has enough juice to last for the length of one disc on playback, around 70-80 minutes, or about an hour when recording. Recharging from flat takes around an hour. External connections include a headphone socket, and dual mode optical digital/line inputs and outputs, so it could just as easily be used a source component in a hi-fi system or in-car player, with a suitable adaptor. Making a recording is no harder than a normal tape machine but there are extra enhancements, including the facility to give each track a title, using the set of alphanumeric keys on the top panel. That's really all there is to it, so how well did it perform?



First stability. If you've ever listened to one of those portable CD players you'll know that  portable is a complete misnomer, no CD player can take more than a light tap without skipping all over the place. MD is different, it has an ingenious buffer memory, so if you give it a whack instead of hearing what's coming off the disc you hear the contents of an unshakeable solid-state memory which holds up to ten seconds worth of audio information, so there's no loss of sound, even if you treat it like a cocktail shaker -- most impressive! Sound quality is pin-sharp, with excellent  clarity and definition. Pre-recorded discs compare very well with their CD counterparts and it proved quite difficult to tell MD and CD apart, in side by side comparisons. However, the MZ1 really came into its own when used for recording. The RZ1 and 727 mike are a cracking combination, sound quality is stunning, with no trace of background hiss whatsoever, but it's the pin-sharp reproduction of everyday sounds that really makes you sit up and take notice. One simple but very effective test for any stereo recording system is to 'draw' sound shapes, by shaking a matchbox around the microphone,  describing simple patterns or shapes in the air. On the RZ1 we found most of our unprimed guinea pigs could 'see' those shapes, when they listened to the replay, with their eye's closed.


And so we come to our camcorder compatibility tests. As there's no way of synchronising the two machines the results are a little rough and ready but we found that in our first test recording all three machines were in almost perfect synchronisation after ten minutes. After 15 minutes the MZ1 and the Sony camcorder had drifted apart by maybe a tenth of a second, the Panasonic S20 was still holding its own. At the twenty minute mark there was no change between the MZ1 and Sony camcorder but the Panasonic S20  had started slip behind, though again probably by not much more than tenth of a second or so. After thirty minutes the differences were still small, no more than a couple of tenths of a second, with the Panasonic machine slightly behind, and the Sony camcorder slight ahead. We repeated the tests a couple of times; on the second  test they all finished together after 30 minutes. In the third and last test both camcorders lagged behind the MZ1 by three or four tenths of a second.



It's difficult to draw too many meaningful conclusions from such simple tests, though  it is apparent that MD speed stability is equal to, or possibly better than VHS-C and 8mm video and it could indeed have a role to play in video movie-making, though without some means of synchronisation it will have to stay on the sidelines as much still depends on the user's reaction times. 



(c) R.Maybury 1993 1803



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