Decca Digital Audio Mastering System

The Decca Digital Audio Mastering System

As a rather proud owner of one of these milestones of audio technology, I thought it worthwhile to include information about it on this site. Having previously written what I knew about the system together with my impressions of the famous Decca Recording Centre in London, the designer of the equipment Mr Tony Griffiths was kind enough to contact me and offer to 'fill in the gaps' in these ramblings. I am therefore highly delighted to incorporate Mr Griffiths corrections and comments into this revised version - with his kind permission. Later, in February 2004, Mr Michael Mailes contacted me with his own first hand experiences as a user of the Decca equipment, and these fascinating comments may be found here

Thank you Tony and Michael.

The equipment on these pages is an example of the unique digital recording system that The Decca Recording Company designed and developed for their own use during the mid to late 1970's. These machines and various other items of pioneering audio technology, were used to record and edit

Decca's classical music output on both on LP ('vinyl') and CD. This was at a time when Decca's recorded sound quality was widely regarded as being the best in the industry. Building on an illustrious history of invention and technical achievement, Decca at West Hampstead developed for themselves a digital mastering system that was to become simply the best stereo recording system on the planet.

Seeking tangible improvements in the many production links between the microphone in the concert hall and the edited master tape, Tony Griffith's team took the experience they had gained in developing an early form of digital video disk system known as 'Teldec' (Television and Decca) and built what was also to become probably the longest lived digital audio post-production system ever.

Remarkably as newer commercial alternatives were to come and go, Decca were never impressed enough to change. Either the sound quality was inferior, or the video-cassette based machines were too cumbersome in use, or both. (Those of us used to linear video editing, will appreciate how time-consuming it can be waiting for videocassette machines to clunk their way through tapes.)

Decca started using their digital system in the late 1970's, and I was lucky enough to witness it still in use in November 1997. This was a twenty year plus working lifespan, which for any piece of pioneering technology is a pretty impressive achievement.

My still operational system (fingers crossed) is I believe one of only three Decca digital tape recorders now left in the UK, and is probably the only one in private hands. It consists of a 20 bit analogue to digital converter, a signal processing unit (codec) with timecode facilities, a modified IVC 800 series helical video tape transport, and an 18 bit digital to analogue converter.

What follows is further background to this machine.

In 1997 the famous Decca Recording Centre in London was closed down and around ten of these recorders were shipped to Polygram's headquarters in Holland for archive transcription purposes.

After over twenty years continuous use, Decca's new owners had decided to abandon this unique recording and production chain in favour of commercial (and now usable) alternatives. The remainder of the thirty five or so Decca recorders and much other unique digital audio production equipment was sold off or scrapped.

In the early 1970's, as a very much younger person vaguely 'in the business', my feelings about digital audio were somewhat mixed. For while the publicized possibilities of this very radical technology (for the time) did indeed seem quite remarkable, and perhaps the recorded quality might actually prove to be 'perfect', the sheer quantity of electronics and serious engineering effort needed to achieve this advance in audio quality seemed quite out of all proportion to the complexities involved. Remember, in those days a very respectable professional analogue stereo tape recorder could be bought new for very much less than £2,000. However with this new Decca digital system, just the IVC 826 1-Inch helical-scan video transport cost rather more than £2,000. On top of which, one then needed to add the significant overheads of two lots of state-of-the-art Digital conversion circuitry and a special signal processor to convert the digitized data stream into something a video tape transport could digest.

Decca's 'works' cost for one of these recording systems was 'about £13,000' (in 1970's money), which perhaps represented for the time a quantity of electronics and expense similar to that of a contemporary mini computer. (A nice PDP11 perhaps.) They had to use a modified video tape transport because digital audio had a much higher data through-put than any computer or computer tape drive of the day could cope with. Though in the longer term Decca planned to use a type of video disk to record the audio. (How far-sighted was that?)

Indeed, the use of modified video recorders of various formats was later to become an accepted way of storing audio 'digits' for some time (as with Sony's U-Matic based 1600/10/30, their later F1 and R-DAT systems etc, but please see also the previous comments).

Be that as it may, the thought of using enough electronics to build a mini computer AND a specially modified heavy duty industrial video recorder just to record slightly 'better' sound at a time when the insides of an analogue FM tuner seemed quite complicated enough thank you, did rather call for the calming qualities of a stiff drink. This was indeed mad and exotic rocket science in those days. The word 'bonkers' seemed fairly appropriate, as all this stuff did seem a bit like using a Saturn 5 Moon rocket to warm the patio (!). Digital watches were though still 'pretty neat' then, but this digital audio stuff was completely on another planet. Oh, and if you wanted to do some simple editing, another complete system (at £13,000) and a lot more gubbins besides had to be put on the shopping list.

Somewhat different to the world of an old Ferrograph, a razor blade, some sticky tape and an editing block (total cost perhaps less than fifty quid including the tape machine!).

Digital audio in those simpler times seemed quite, quite mad, and perhaps still does if you are talking true high fidelity. But here we are thirty years later and everything is all bl..dy digital now. Quite mad, even the lap-top used to put this web site together can record audio direct to its disk via a 'virtual'

mixing desk. (As of course can all PC's.)

Quite, quite daft.

But there again I am just an ageing Hi-Fi nut who likes to use valves to listen to his Jazz; a consumer and not a practitioner. While the ex-BBC Mr Tony Griffiths and his team were very 'hot' practitioners indeed, fresh from wrangling with digital video processing, slow speed telecine machines and floppy (vinyl!) disk television recorders. So putting a bit (sorry) of digital audio on to a reliable workhorse of an IVC video recorder was not thought difficult. In Tony's words; 'apart from the a/d development, the digital processing posed no problems'.

This is of course a question of perspectives...

What follows is some rather vague recollections of how I obtained this equipment and of the last months of the famous Decca Recording Centre before it closed (I believe that the English Ballet, Opera and some remnants of Decca's technical team remain in the premises).

Oh, and having done a number of Internet searches on 'Decca' I am disappointed to find any number of references in connection to the many famous artists associated with the company, but none actually about the recording facility itself. What follows might redress the balance slightly.

My own involvement with Decca came about by in interest in old (and thus affordable) television technology. In the early 1980's the first generation of educational television equipment was being replaced by newer cassette based colour systems. This meant that a lot of rather nicely engineered

reel to reel 'gubbins' just mostly got thrown away. To some of us this seemed a rather good opportunity to acquire for very modest sums some highly interesting and once serious bits of television engineering to play with.

I do freely admit that I sometimes use the IVC service manuals as bedside reading and unlike more orthodox (Stephen King?) material they are a rather good read. Of course such stuff was written before professional video equipment became just another multinational product. However, having once got to grips with an aged Ampex (who also wrote very good manuals) 'A format' VTR, it became apparent that similar machines made by the International Video Corporation might even be more interesting, especially as most of them could be converted to colour just by plugging in an additional (though as I was to find out vanishingly rare) 'heterodyne board'. In the end, I was to get my hands on four IVC recorders, two colour boards and had 'shares' in a fifth time-lapse machine (The Gyr modified IVC time-laps recorders ARE rarer than rocking horse poo, absolutely worthless - but vanishingly rare).

Now wallowing in Jurassic video I didn't even bother getting a nasty VHS machine until years later. As the rather unpredictable delights of 1-Inch reel-to-reel video seemed to be a more exciting if rather less portable alternative. I did though find it impossible to get films at the local hire shop - 'one Inch? what's that then mate?'

The only problem of trying to keep a whole load of steam video recorders in working order is of course obtaining spares, and in particular the fragile, and all too consumable video heads. Exercising my mind on this subject I dimly recalled that Decca Records once had a digital recording system that used 'my' IVC machines, and not being afraid of using the phone, I called them up to talk heads and spare parts. Well, not only did they once use IVC machines, but they were still very much using them and in fact were currently recording all their serious music on them. While not able to help me with a source of affordable video heads (theirs were obtained at serious cost from California I believe [Spin Physics?], we did though sort-of keep in contact.

Cut to ten years later when I was about to move house and was looking for good homes for some of 'the collection', might Decca be interested in some of my IVC stuff for spares? Well a quick phone call to my long term contact rather turned the tables on me, in that he asked if I might like to acquire some of their IVC stuff as they would be closing the Centre in a few months and would be getting rid of most of it. My ears pricked up rather, as this might include some of the digital audio recording gear as well.

Those few months turned into a couple of years, but eventually I did indeed end up with various new toys, including the intact digital audio system you see here. Actually it was rather a privilege to have seen the Decca Recording Centre in full swing just before they shut it down, and I regret not taking a camera along. We made two visits; the first on 19th November 1997 was just to have a general look around and to see what might be available. The second made a few weeks later (getting near

Christmas I think), was to make collection.

At the time of our first visit the facility was still very alive. Indeed it was remarkable to see the extent to which Decca had developed their unique though by then very venerable digital recording chain, and how this system was interfaced to their Sony 1630 CD mastering equipment.

When we eventually found the place, Decca's famous and historic facility looked from the outside to be a rather anonymous and aging warehouse. Having just passed the rather posh Abbey Road studios (about a long microphone's throw away) this equally famous 'Recording Centre' was a bit of a contrast. The ground floor seemed to be mostly made up storage facilities for their location recording equipment. Though being a wheelchair user, a fair proportion of the building was inaccessible to me. Within this storage area, their extensive collection of location equipment was housed in many 'well-used' flight cases, piled up on rows of 'Dexion' shelving.

Rather like it was Christmas, we excitedly rushed around opening up cases and peering inside at the goodies. A box of microphones here, something unknown there, a digital processor here. Against one wall lurked a couple of ancient and complex 3M digital multitrack recorders (yes, not only did they

once make recording tape, but they also made the first commercial multitrack digital tape recorders), against another wall were many assorted hydraulic 'pump-up' towers and bits of microphone rigging. Adjacent to this area and at the front of the building, there was an internal parking bay and a general workshop area.

Having ascended in the large service lift (in pitch darkness actually as the light had blown), we came out into a bright modern looking open 'hospitality' area. I recall seeing a billiard or Ping-Pong table, sundry bits of seating and various tea and coffee making facilities. This was much more like a contemporary office reception area, or indeed what recording studios seem to look like these days. I recall lots of light wood and Grey painted surfaces.

Significantly on one wall was a clock with its face fashioned from an LP, with hour batons marked 'DECCADIGITAL' (12 letters yer see). From this recreation area we were taken through a couple of double doors, past sundry (Decca modified) Studer A80 recorders skulking in the corridors, into

what proved to be a sort of editing and post-production facility. Adjacent to this room were 2 or 3 sound proof editing suites. To our right on the other side of a glass partition wall was an office or storage area. To the left were perhaps three substantial 'watertight doors' (like in submarines but bigger) separated by well stuffed (with buttons, displays and winking lights) six foot high equipment bays. Spread out in front of us were a collection of what at first sight looked to be old Mahogany radiogram cabinets. Each of these rather randomly parked and incongruous objects proved to contain a Decca modified IVC 1-inch videotape transport. These 'radiograms' were actually Decca-built acoustic enclosures for those rather noisy IVC machines. Within each of these enclosures resided a tape transport, face up under a smoked Perspex lid.

While we were chatting we could see that some of these machines were run-up and in the process of 'rocking and rolling' as one of the editing people worked away behind one of the 'watertight' doors. As far as we could see, mostly everything seemed to have been exclusively Decca in origin. The equipment racks contained in-house processing, time code and editing electronics. I had assumed that bits of PC lurked inside, but this equipment was designed before IBM processors were fast enough to do the job, and were actually Decca designed computers based on AMD 68000's.

The editing rooms themselves were quite small, and were perhaps some 10 or 12 feet square. They were lined with dark-wood effect acoustic treatment. Roughly in the middle of the room was a control 'desk', on which was placed a PC type computer monitor, a PC keyboard, a commercial video-editing controller, and a basic Decca digital audio mixer. Most of this stuff looked fairly current.

Digital peak level metering was done via the computer monitor, though for making analogue copy tapes for artist's approval a pair of PPM's were used. Did you know that Decca and not the BBC invented the Peak Programme Meter? I didn't.

All the sound mixing was done in the digital domain. Each of these once state-of-the-art desk used digital dither to remove quantizing distortion, and had two channels of digital equalization. They also had a clever programmable notch filter that could synthesize up to 3 notches of varying width anddepth. This was used to 'remove anything from Hum to TV line frequency whistle'. I am not sure if many 'modern' desks even have this ability, which was often used when they were re-mastering old analogue tapes.

About four feet in front of the desk and some six feet apart, were placed a pair of stand-mounted ( 1-inch 'speedframe?) B&W 801 monitors. They were facing inwards towards the operator and were driven by an HH Mosfet power amplifier (500 Watts per channel?). I have to say that I was not very impressed with the sound in that editing room, it was loud enough though. But there again, this monitoring system was not for sound balance or ultimate quality evaluation, but was just for making sure that the edits were good and there were no obvious problems with the recording.

The computer monitor displayed the music's 'waveform' together with a time cursor. Decca were the first users of video editing software for audio post-production, and they developed their own ways of doing this which were years ahead of anyone else. However, this very advanced way of doing things was at first regarded with suspicion by some users.

As with linear video-editing, the various edit points are stored in the edit control unit's memory, and each edit can be rehearsed, and if required the edit points can changed before actually making the edit. With this equipment edits (which are in fact very rapid cross fades between two playback machines onto one recording machine) are made with an accuracy down to one digital sample (a 1/48th of a second).

This was all done before PCs were fast enough and therefore Decca built their own editing computers and memory systems. Semiconductor memory was also used to store a limited amount of the actual digitized audio itself. This was to speed up the editing process while the mechanical tape machines 'caught up'. This was far quicker in use than Sony's Umatic based 1610/20/30 digital audio system.

What we had the privilege of seeing that day was a very fine example of what can be accomplished when you let clever people who are experienced in one area of technology (in this case television and digital television recording), bring this knowledge and creativity to bear in an alternative direction (that of sound recording). In Decca's case this was a very fortunate irony, for while their attempt to develop a 'DVD' some twenty five years ago seemingly failed, the spin-off from this hard won experience allowed them to come up with an outstanding sound recording system that was years ahead of everyone else. On reflection, this seems to be the exact opposite of how things usually work these days. Useful 'Spin-offs' were once the happy by-product of all sorts of 'blue-sky' thinking and far sighted management, even in the poor old UK. Unfortunately, these days we seem to have replaced the clever people with focus groups, and have allowed management to be ruled by stock market gamblers. The results are abundantly obvious.

Er? oh yes, back to 1997:

It was quite a revelation to realize the amount of editing done to something as 'pure' as a classical music recording. It was not at all a question of just setting up some mikes in the right place and hitting the record button. For perhaps several dozen and possibly hundreds of edits were carried out on each work. So much 'for the closest approach to the original sound'. In this case possibly, sound recorded at many differing times of day and possibly location. (Which is actually quite usual with 'pop' music.) But Mr Griffiths picks me up on this and remarks, 'The sound was always that at the performance but the musical accuracy was much better. This results in a play back free from the annoying defects, which become recognizable points of anticipation after a few playbacks.'

He is of course quite right, I was just looking at it from the rather simple perspective of a naive Hi-Fi enthusiast.

While the big loudspeakers were used most of the time during the editing, the operator actually checked the quality and integrity of each 'splice' with a pair of Beyer headphones.

Almost all of the Decca system was of their own design and manufacture, at first with their own soldering irons and 'Veroboard', though later subcontractors were used. But most final assembly and programming remained 'in house'.

The grand plan was to acquire on location correctly balanced digitally recorded stereo recordings and then keep the whole of the rest of the 'post production' process in the digital domain. This avoided the inevitable generation losses of conventional analogue recording. In addition once the performance was 'in the can' it could be treated just like making a television programme complete with time code. This enabled non-destructive editing and many theoretically perfect generations to be carried out by fairly standard (as discussed) video post-production methods. Just as impressive, was that Decca were able to make early 70's IVC video transports behave like modern time code 'chase locking' devices. It was remarkable to see these 'clunky' twenty five year old IVC's behaving just like they were relatively modern and slick Ampex VPR-6 or 80 broadcast 'workhorses'.

Tony advises me that Denon in Japan and Tom Stockhom in America also had developed very early digital audio systems. But Denon's was only 12 bit (using video recorders), and Mr Stockhom's used a multi-channel instrumentation recorder. Stockhom also attempted recording audio direct to a mainframe computer, but apparently this took 'most of the night to upload'.

Decca were quite aware of these systems, but their recording teams said "If it won't do what we normally do, then the won't use it" and of course their system was to do rather more than any of us had realized.

During our first visit we also saw a couple of other mixing suites that contained more advanced digital facilities, including EQ and digital time alignment for microphones (another Decca first). One lone 'special' digital mixing desk sitting in solitary splendor (which implied a recording area for it in the building somewhere) was also fitted with advanced 'endless belt' type digital faders, which were highly 'cutting edge. Their 8 channel mixers used 64 bit arithmetic, with dedicated and home brewed TTL processing for reasons of speed of calculation. (This was in the days of the mighty Cray-1 supercomputer which used similar simple circuitry for reasons of speed.) Both DG and Phillips were supplied with versions of this mixer for their own mastering 'systems'. Recording (perhaps one should say 'memory') for these various suites seemed to be provided by those IVC transports lying around in the central post-production machine area as described above.

Sadly this was all to come to an end, and was to be transferred to Polygram in Holland. My understanding was that it had been decided to use normal commercially sourced equipment in future, and not to continue with development or use of the special 'custom' Decca equipment. This would include their next generation of a newly developed magneto-optical system as well. In fact some ex employees had already departed to set up Gennex. Who manufacture the very well regarded GX series of optical recorders, which I believe build upon 'Decca' technology.

During our various conversations it also became apparent that Decca had never been very impressed with the newer commercial digital systems as they arrived. They were either too slow in use, had inferior error correction, or only had 16 bit resolution. Decca would have been happy to change, but what they had built proved rather too good, and too cost effective. And so in the face all that commercial digital stuff to arrive from the likes of 'Sunny', 'KVC' and 'Quanasonic', they happily carried on with their 'home made' electronics and obsolete IVC recorders. New apparently did not mean better...

They did though have to interface their system with CD mastering equipment, and in one corridor of the centre was a row of racks containing extensive Japanese Umatic equipment, opposite a lone IVC 700 series transport for master tape playback. (The Decca Centre was a bit of a 'rabbit warren' actually, and seemed to be extended into a number of surrounding buildings)

Unfortunately, these remarks have been made over seven years after the events, so a lot of detail has fallen out of my brain. It was though a privilege to have briefly witnessed those famous recording studios in West Hampstead, and to have experience first hand Decca's 'brave new world' sound recording system. A system which was in fact a rather stunning and far-sighted achievement, that turned many previous conceptions of sound recording on their head, including my own.

As an audio recorder I am pleased report that my venerable specimen does indeed perform very 'transparently'. On listening with modified Quad 11's into ELS57's, or via one of the better Stax electrostatic headphone systems, I can detect no difference between record and playback, which is of course as it should be. Actually I have the strong impression that this Decca machine is probably far in advance of anything I can throw at it. Indeed I would probably use it much more often, if it wasn't for the fact that the IVC transport is thirty years old and will need a complete rebuild sooner rather than later. This might be a bit of a challenge to someone with no manual and only a few spares to hand.

It does though make a pretty good museum piece.

G.Mancini, March 2004 (Revised April 2005)