In an age where period material is extensively sampled, the term 'oldie' is becoming less pejorative. Modern restoration techniques not only remove noise; they can even restore the original ambience to historic material. With a vast catalogue of vintage recordings, Ace Records' re-mastering operation is second to none. Magnus Schofield visits Sound Mastering for a 90s makeover...

"At some point, you have to have a reference", protests Sound Mastering's beleaguered engineer Duncan Cowell. Digital audio may have revolutionised the business of remastering, but further down the food chain, it's been grist to the mill of the audio neurotics. And when the client is a re-issue label like Ace Records, you're talking about a record-buyer with the mentality of a trainspotter. Whether it's an omission from a 1950s discography, or a spot of differential frequency limiting, if it isn't how they remember it...

'How they remember it', is seldom how it really was. Apart from the fact that most of them weren't out of nappies at the time, what collectors are apt to forget is that mastering engineers have always tailored the final mix to reproduction standards of the day. Play an old 45 on a period portable, with its ceramic cartridge and valve circuitry, and you'll hear an EQ that's as sympathetic as it is sweet. It's no use modern engineers anticipating the same signal path, with valve amps nowadays a rich man's hobby, and the characteristics of D/A converters about as predictable as the Singapore Futures Market.

"The best Sound Mastering can do", explains Duncan, "is standardise on a flat room with a flat frequency response. If a client has particular requirements, they can always sit in on the session".

With its two large baffle screens and angled rack units, Duncan's editing suite resembles the cockpit of a spaceship. And at its focus, sitting shrine-like between the monitor speakers, is an oscilloscope. As we were to discover, the 'scope has an increasingly important role in protecting Sound Mastering's clients from the depredations of the bootleggers.

To the extent that digital remastering has given a new lease of life to a wealth of historic material, operators such as Sound Mastering have become victims of their own success. Just as restoration techniques have become more efficient and affordable, so the rewards have grown, in a sector of the market where artist's contracts and A&R budgets are non-existent.

Clients such as London's Ace Records or Germany's Bear Family may take the trouble to buy catalogues or pay licensing fees, but there are plentiful re-issue houses with no such scruples. Unlike the British Library, there's no public money or Arts Council grants to encourage the archivists, and discourage the pirates. Many of the acetates and master tapes Ace bring to Sound Mastering might otherwise decay or disintegrate, but for companies with more of an eye to profit than posterity, the potential rewards are enormous. In an age when CD-mastering technology filters down to the provinces of rural China, copyright owners have to be increasingly imaginative in their 'fingerprinting' techniques.

Duncan joined Sound Mastering after Audio College, and a spate of dance remixes which exploited his analogue editing skills. "It was the time of 'N-N-N-N-Nineteen'", he recalls dryly. Known then as the Digital Editing Suite, the company's evolution into Sound Mastering mirrors the demise of 'digital' as a buzzword, and the realisation that analogue and digital technologies are more complementary than contradictory. Duncan gives short shrift to the idea that recordings can ever be truly 'DDD', when at some point the signal path is bound to encounter an analogue mixing desk or signal processor.

Adam Skeaping founded the Digital Editing Suite at a time when the world of classical music was rushing to exploit the improved fidelity of CD. Virgin Classics and 'indie' classical label Hyperion were two of Adam's biggest clients. Their catalogues may have overlapped, but their values couldn't have been more different. To this day, Adam distinguishes between, "the accountants", and, "the good guys", ascribing the fate of Virgin Classics to their mercenary ethos, and the success of Ace to their academic rigour. A Bob Wills or Jimmie Rodgers anthology may not inspire him musically, but at least he and his client are working in a spirit of mutual respect.

Bob Jones is the walking encyclopaedia of the operation, an ex-Decca engineer and lifetime r&b collector with a nose for tapes of dubious provenance. He's also the analogue diehard, most at home with an Aphex compressor and limiter, and a pair of vintage Technics 12-band parametric EQs. While the Technics can still cut the mustard (or more often, the bass boom), Duncan opts for the surgical accuracy of a Valley Dynamap digital compressor/limiter, which is capable of splitting frequencies, limiting a bass guitar without affecting a snare drum, for instance.

Some engineers will record raw audio to hard disk, but Sound Mastering have refined a technique of preliminary EQing. Rather like one of those disposable razors, this involves making an initial sweep, grooming and preening the signal in anticipation of cuts further down the chain. The first of these is performed by the Cedar De-Clicker, a £12,000 piece of kit whose unique computer software has made it the industry-standard of remastering studios. The De-Clicker 'understands music', or at least the gradients at which its waveforms usually wax and wane. Digitally-generated dance music might conceivably present a challenge, but by the same token, it's unlikely to be a candidate for restoration. Its waveforms are less likely to be disfigured by the kind of, 'unnatural transient' which is the De-Clicker's stock in trade.

"It's not unknown for Nick to physically reassemble a shattered disc, and retrace the groove through a shellac jigsaw-puzzle"

If the De-Clicker has a fault, it's a tendency to 'soften' rather than entirely delete longer, beefier scratches. It's the lesser of two evils, when their wholesale removal would exceed our threshold of perception, and resemble a jump or skip. On such occasions, feeding the signal through twice is an option, although its side-effects in terms of EQ may then need to be remedied. Adam and Duncan may be sold on the De-Clicker, but de-hissing devices are another matter. It's an area where the labour-saving benefits are not so great, and an experienced engineer can still achieve a lot with a good equaliser. Adam winces as he recalls systems such as No Noise, which he remembers, "taking the life out of', the music.

Sound Mastering are equipped to restore original recordings of every format. Not every owner of master tapes will release them, in which case they have to settle for another engineer's DAT copy. Otherwise, the first stage is to make three DAT copies of their own, from the original tape, disc or acetate. Nick Robbins acts as chief cook and acetate-washer, gently bathing the 16" discs in a weak solution of washing-up liquid, sponging grime and detritus from the grooves. Any dedicated collector of car-boot or fleamarket vinyl will confirm the miraculous results this can achieve.

Bespoke hi fi manufacturers Pink Triangle resolved the problem of transcribing the 16" discs, customising one of their decks with a oversized glass platter and mono cartridge. "Mono-ing alone removes a lot of the hiss", explains Nick, "because the scratches are out of phase". Since installing the facility, Ace have been deluged with acetates. As an imperfect art, dubbing from disc demands resourcefulness and imagination. It's not unknown for Nick to physically reassemble a shattered disc, and retrace the groove through a shellac jigsaw-puzzle. "In this game", he explains, "there are no rules".

Paradoxically, 60s and 70s stereo masters often present greater difficulties than their mono precursors. Technology had advanced faster than the proficiency of the average engineer, who reacted to multi-tracking and reverb like a kid in a candy shop. Engineers also changed as a breed, from what Duncan describes as, "technicians in white coats", to, "jumped-up roadies who happened to be in the right place at the right time".

Nor were upwardly-mobile roadies the only effect of 60s values in the recording industry. Just as the oil crisis pared albums and singles to wafer-thin proportions, so environmental lobbyists shamed Ampex into abandoning the traditional whale-oil formulation of their tape binder.

Stampeded into action without normal procedures of research and development, Ampex substituted a synthetic binder which has since begun to hydrolyse. The result is a engineer's worst nightmare, in which polyurethane and magnetic oxide part company, and historic recordings end up curdled on the tape head.

Ampex have gone some way to resolving the problem, with a technique of gentle baking which expels moisture from the chemical sandwich. It provides a window of opportunity, during which engineers can retrieve the tape's contents, before moisture re-invades at twice the previous rate. But it takes time, and gives the tapes another transatlantic journey before Sound Mastering can get to grips with them. As a result, Adam has improvised, with his own design of slo-cooker, which achieves the same temperature and humidity, but without the trouble and expense. In these circumstances, Sound Mastering's three DAT copies will represent, 'new original masters', and it becomes all the more important they don't fall into the hands of the industry's cowboys.

To this end, Sound Mastering have pioneered a system of 'fingerprinting', which will withstand any amount of processing, and promises to make their handiwork identifiable in all circumstances. Detectable only with an oscilloscope, it relies on a system of phase reversal, at points in the recording known (and logged) only by the engineer. Affecting as it does periods of as little as 1/44,000 of a sec, it's entirely inaudible and impossible to locate. Nor is it susceptible to 'defeat' circuitry of the kind SCMS or similar spoiler signals have spawned in the past. In a field where, as Adam puts it, "whoever does the best homework first, does it for everyone else", the remastering engineer can't leave anything to chance.

Disk space is the key word in hard-disk recording, and Sound Mastering have invested heavily in the PC-based SADiE software. It increasingly supercedes the AMS Audiofile system which cost £65,000 ten years ago, and which is prohibitively expensive to upgrade. 2-3 CD's worth of material can be held on the Audiofile at any one time, but Ace and Bear Family releases commonly extend to 10 CD boxed sets, whose track listings are subject to change up to the last minute. As a former label boss himself, Bob is the resident expert, and contributed to Bear Family's recent Duane Eddy anthology as much in terms of research as sound engineering.

Duncan nowadays auditions finished CD masters with a Pink Triangle D/A converter, by-passing the bog-standard converters of a domestic CD machine, and reproducing the fabled 'warmth' of vinyl. It's easy to understand his preoccupation with, "the constant conundrum of sound quality", as he struggles to rein in the screaming upper mid-range of tunes that were designed to leap out of jukeboxes. It's like sandblasting an old sculpture; enough spit to get the dirt off, but not so much polish as to efface the detail. Unlike stonecarving, however, at least a careless stroke of the chisel isn't irreversible. Digital technology has seen to that.

At the centre of the newest working environment at Sound Mastering is the new SADiE (or Studio Audio Disk Editor) system, running on a PC. The system is more flexible than the AMS Neve Audiofile, in that a new and higher capacity hard disk, a faster processor, and more RAM can be added at leisure, and at a fraction of the cost. It also provides a more user-friendly graphic interface, running under Microsoft Windows. The only danger is that showing the waveform in such explicit detail, "can make you paranoid", as Duncan puts it.

SADiE was first reviewed in Music Technology in January 1993, and has since become the standard in the re-mastering industry, with many back catalogues (including The Who's boxed set) relying on its sample-accurate editing to eliminate glitches, noise, and other audio mishaps. It can be run on any 486 PC with a minimum of 8Mb of RAM and Windows 3.x. Two free 16-bit expansion slots are also required, for fitting an X-S digital audio processor, the X-ACT analogue convertor and SMPTE timecode interface. The processor incorporates an SCSI interface for fast transferral of data to and from an external hard disk, or removable optical drive. The card also allows the synchronisation of MIDI devices (for MTC) via a built-in MIDI interface, and rear panel RCAs for stereo (or optional four channel) analogue output. On the rear panel of the X-S card are digital RCA SPDIF connections for input and output to DAT, and a 25-way D-connector for AES/EBU digital audio.

The software is constructed into three main windows; the first is a level control, acting as a kind of mini mixer with controllable sliders, mute and solo buttons, and a level meter. The second is the Transport window, where all the usual tape functions reside, plus a counter and facilities for setting location memories for markers and loop points. The third is the Edit window, where the sampled waveform is displayed in graphic form, making the process of audio manipulation far easier than guessing with a list of numbers. Sections of audio can be zoomed in upon, using the mouse to highlight the desired region; these can then be edited separately from the rest of the sample. All edits like cross-fading, cuts and pastes are performed non-destructively, allowing the sample to be re-edited time and time again, until things are right. Other impressive editing functions include EQ, compression, time stretching and varispeed.

How this applies to sound remastering, or indeed mastering, is in the transferral from Sony U-Matic video tape (on which masters were traditionally stored) to CD, with as little fuss as possible. Although not used by Sound Mastering, SADiE can also provide a quicker way of creating a finished CD (using an external CD-R). The CDR (Red Book) or DDP Exabyte formats can be used to transfer the audio faster than 'real time'.

Other users of the SADiE system include Dolphin studios in Frankfurt, The Roundhouse, where it is used for creating Red Book CDs (using the above techniques). Sprockets and Bytes also used it to synchronise film for the recent Billy Connolly Comic Relief reports from Mozambique, plus numerous other remastering projects including Elton John, The Who and Gong. Danny McAleer

For more information, contact: Studio Audio and Video, (Contact Details).

An essential component in Sound Mastering's pre-editing process is noise abatement and general sound tidying, using two modules from the Cedar 'Series 2' range. The DC-1 De-Clicker was the first module Sound Mastering invested in, and has become a lynchpin of their re-mastering process. With this device, the more prominent clicks are removed, and less obtrusive ones 'softened', before any other processing is done to the signal. Its sophisticated software makes educated guesses about the signal's shape before the recording was damaged.

There is a dramatic reduction in extraneous noise, although Duncan often applies a little EQ afterwards to the signal, just to ensure that no character has been lost.

Since the interview, Sound Mastering have acquired a CR-1 De-Crackler, to complement their DC-1. This device enables them to more efficiently remove crackle and buzz from all manner of audio sources including vinyl and acetate, thus producing a clearer signal into Audiofile or SADIE for editing. The rear panel connections are the same as the DC-1, offering both RS232 and MIDI interfaces, for operating the module under remote computer control. There is also the option of controlling both units with SMPTE/EBU timecode, via an add-on interface board. Audio connections come in the form of digital RCA-type SPDIF (16-bit) and XLR-type AES (24-bit) inputs and outputs, plus balanced XLR analogue inputs and outputs.

Both modules cost around the £10,000 mark, but for this hefty sum provide professional quality audio processing. There's also real-time control of parameters, with additional battery-backed memory for storing presets, all with an apparently simple user interface. Danny McAleer

For more information on the DC-1 and CR-1 restoration devices, contact Cedar Audio, (Contact Details). Or contact: HHB, (Contact Details).