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Computer Musician

Studio Focus

Durham University Electronic Music Studio


Custom-built 32/16/2 mixer.


The electronic music studio at Durham was established in 1970 with the modest resources of two Revox tape recorders, a portable Uher mixer, a secondhand jackfield and a VCS 3 synthesiser. At that time electronic studios in Britain were few and far between, nonetheless we were quite unprepared for the widespread interest shown in our tentative first steps. As the very existence of this magazine so clearly demonstrates the subsequent explosion of activity in the field of electronics and music has long since eclipsed those early pioneering days and left institutional studios such as ours with a dilemma, either merely to duplicate commercial studios by purchasing and updating manufactured equipment, or to develop alternative and hopefully more attractive systems by custom design and development.

Durham chose the latter approach at a very early stage, and has sustained a programme of research and development as a major priority, under the direction of the author. Technical engineering was initially spearheaded by John Emmett, spirited away by the research division of Thames Television in 1976. Since this date responsibility for hardware has been in the hands of Ron Berry, building up not only the resources for the analogue studio, but also more recently all the special interfaces required for our second, all-digital studio. (Regular readers of E&MM will recall Ron's article on the Home Electro-Musician in July, 1983).

Analogue Studio



The two studios will be described separately, although it is important to stress that composers will often combine the resources of both studios in realising a piece. In the analogue studio two VCS 3 synthesisers and a keyboard are the only items of commercial electronic music equipment. Even these will be released for live group work when a further bank of envelope shapers and ring modulators has been constructed. The rest of the system consists of the following custom-built items; a 24 element oscillator bank, a digital pink noise generator, 2 third-octave filter banks, 4 adjustable filter units, a stereo frequency shifter, 4 signal processors, a digital delay line, and a spectrum analyser.

The oscillator bank is divided into two groups of twelve oscillators, one group producing sine/square waves, the other ramp/triangle. In designing this unit particular emphasis has been placed on frequency stability, freedom from interaction (eg. locking together), and waveform purity; features not particularly notable in commercial voltage-controlled designs. For composers brought up on synthesisers it is usually a pleasant surprise to discover that it is possible to combine several oscillators to create rich and stable textures which do not drift apart during a break for tea. The pink noise generator is integral to the spectrum analyser, its digital design ensuring a distribution of noise energy through the audio spectrum sufficiently smooth to calibrate the analyser itself, as well as being available as a studio sound source.

The two filter banks each consist of twenty-eight fixed frequency filters, wired in parallel to encompass a range of nine octaves. The gain control for each filter may be adjusted from +6dB to -infinity, providing a shaping facility significantly more powerful than a conventional equaliser. The four adjustable filters may be switched between high pass, low pass, band pass, band stop and all pass modes, with a 'Q' factor variable between 1 and 200. Coarse and fine tuning controls allow accurate frequency tuning, matching the specification of the oscillator bank.

This emphasis on manual control facilities, so much a feature of studios of the '50s and early '60s might appear distinctly old fashioned. It is important to appreciate, however, that the range of music produced by a studio such as ours is very broad, stretching from rock to the avant garde. Towards the latter end of this stylistic spectrum the desire to work more intimately with the components of electronic synthesis increases sharply, hence the need for more precise control over each parameter. Voltage control networks are still important as a facility for adjusting several parameters simultaneously, and sequencers provide a useful means of recording these changes. The freedom to 'play' systems, however, must be weighed carefully against any consequential loss of accuracy in the sound generation process itself. As will be seen shortly our all-digital studio overcomes all these drawbacks, but not without producing one or two of its own.

The stereo frequency shifter provides a facility for modulating applied signals against an internal sine wave generator to produce either sum or difference tones. A conventional ring modulator, such as that available on our VCS 3s, generates both sum and difference tones simultaneously. Whilst the resultant effect is a rich spectrum of sound, the unavoidable mixing of these products often results in a harshness which restricts their usefulness. The ability to generate these sidebands independently is thus invaluable when exploring the more subtle features of this modulation technique.

The signal processors combine the characteristics of a number of commercial devices and a few of our own in a single unit. Incoming signals may be subjected to varying degrees of compression, expansion, gating or level inversion as required, an adjustable level detector determining the point of triggering, and variable attack and decay circuits the speed of response. Side-chain filters may be switched into the level detector feeds to allow the units to be activated by particular frequency areas, for example the thump of a drum or notes from a bass guitar. The voltage function generated by one processor may be used to operate another, particularly useful when it is desirable to gate one sound with another. The digital delay line was built in the early 1970s and uses outdated technology. It has its uses, however, not least as an effects unit for frequency modulating incoming audio signals. This is achieved by voltage controlling the internal clock which determines the speed at which sound samples are digitized and subsequently resynthesised. In view of the intervening delay, sounds may thus be coded and decoded at different rates, producing FM effects more usually associated with digital synthesisers such as the Fairlight or the Synclavier.

Sequencer facilities may be provided via the digital studio. This particular link, however, is not at present encouraged for reasons of system efficiency, and a microprocessor controlled unit is under construction to service such requirements. This particular technology is now so cheap and powerful that custom design is far more attractive than any commercial unit.

The analogue music studio.


Flexibility



The studio mixer is a 32/16/2 desk, custom-built to our own specifications. Comparable large commercial mixers are primarily intended for conventional recording and broadcast environments and are not entirely ideal for the more specialist requirements of the electronic music studio. In many situations it is desirable for the mixer to be used as an extension of the treatment facilities described above. Complete flexibility has thus been a design priority. Any input channel may be routed via simple thumbwheel switches to any output channel, or panned between any pair of channels, or connected to any one of four joystick controls for quadraphonic manipulation. Spatial positioning and movement, whether in stereo or quad, are important features in many electronic works, and the flexibility of this arrangement has proved very popular.

Reverberation facilities consist of a Great British Spring, accessed via a pair of echo sends on each input channel. Equalisation facilities consist of six units per channel, spaced 1½ octaves apart from 50 Hz, with a variation of + or -24dB, this particularly wide degree of variation reflecting the role of the mixer as a treatment device. For straight mixing the equalisers may be switched out completely to ensure a perfectly flat response. Simple VUs indicate the level on each input channel, and output levels are monitored via a bank of BBC pattern PPMs. Input gain selectors, phase inversion switches and microphone monitoring facilities complete the range of facilities.

Such a large mixer offers many advantages, in particular the facility to treat the unit as a series of smaller mixers by dividing input and output channels up into groups. The system can thus be configured at one go for several stages in the preparation of a work without the need for endless repatching. The patch system itself is unusual, for in place of the conventional patch bay of jack sockets and interconnecting leads we use a pair of pin matrix boards. Despite their size (58 x 74 holes and 38 x 33) composers find them simple to use and very easy to check, for in place of the usual mess of intertwined cables one is faced with a neat arrangement of pins. Pin patch systems have generally been viewed with some suspicion, doubts being fuelled by some very badly assembled versions in early synthesisers. Our experience over ten years, however, has more than justified our choice. A damaged pin is quickly replaced at insignificant cost, and we have never experienced a single broken board contact. Even the inevitable spillage of a cup of coffee, after the initial interesting effect of everything shorting together, has been quickly cleared up with no lasting legacy of dirty contacts. Careful screening of all cables at installation and attention to earthing points gives us a crosstalk figure between adjacent channels better than -75 dB, with a hum figure lower still.

The recording facilities consist of six A77 and B77 Revoxes and two multitrack machines, one ½" 4-track, the other 1" 8-track. Brenell transports have been used for the latter, all the electronics being custom built. In addition a ¼" 4-track Teac is available for running off performance tapes. Two Revoxes are fitted with the manufacturer's + or -50% speed variation controls. A further two have been studio modified to provide a variation between dead stop and flat out, in practice about 24" per second. An accurate indication of tape speed can be obtained by displaying the speed of capstan revolution on a frequency counter. Noise reduction facilities consist of a bank of Dolby A units, and quad monitoring is via Quad amplifiers and Tannoy loudspeakers.

PDP 11/23 minicomputer with peripherals.


Digital Studio



The digital studio, established in 1981, was the first of its kind in this country, although others are now following our lead, notably the University studios at Nottingham and York. The equipment consists of a PDP 11/23 minicomputer with 192Kbytes of memory, 10 megabyte hard disk and dual floppy disk storage facilities, 2 VDUs, a line printer, various I/O ports, a programmable clock, and custom-built, fully buffered 16 bit stereo digital to analogue and analogue to digital conversion facilities, capable of operating at speeds up to 50kHz. A special bit slice hardware 'floating point' processor is incorporated, allowing mathematical calculations to be executed at speeds approaching those attained by much larger machines.

Reference has already been made to large digital synthesisers such as the Fairlight and the Synclavier, now to be seen regularly on stage in rock and pop concerts. Avant garde composers too have been exploring their facilities in increasing numbers as one by one institutional studios across the country scrape up the £25,000 or so required to purchase one. What is not generally realised is that these synthesisers, based on microprocessors, are derivatives of research and development into digital synthesis, initiated as long ago as 1957 by Max Mathews, working at Bell Telephone Laboratories, New Jersey. Working entirely in software, on large computers, Mathews constructed a series of MUSIC programs, further developed by others during the '60s and '70s to become the main compositional facility at many of the main international electronic studios, for example IRCAM in Paris, and Stanford in California. At MIT, however, Barry Vercoe developed a version known as MUSIC 11, written in machine code for the PDP 11 range of computers, and it is this package which has been installed at Durham on hardware costing significantly less than the commercial synthesisers discussed above.

MUSIC 11



The characteristics of programs such as MUSIC 11 are rather different to those of a commercial synthesiser, so it is potentially misleading to make a strict comparison. A few general points nevertheless may usefully be made. Fairlights and the like are performance orientated systems with an immediate response, offering the user a finite range of options, for example up to 8 voices at any one time. Manufacturers, however, have generally been reluctant to release details of the latter for fear of revealing trade secrets, and their insistence on non-disclosure agreements has restricted the accessibility of program libraries and programming techniques to others. The preferred method of operation, via the keyboard and special console is nevertheless very versatile and adequate for many purposes.

MUSIC 11, being entirely a software simulation on a standard computer is restricted only by memory space and processing power, allowing the composer a far wider range of choices.

Specifying upwards of 48 oscillators, using a variety of waveforms and envelope characteristics, for example, presents no difficulty. Indeed the degree of control which may be exercised over individual parameters is limited only by the willingness of the composer to enter sequences of instructions. Further, since the programming language is freely available to all, no restrictions are imposed on the interchange of information.

The tradeoff for this enhanced versatility is a lack of immediacy, for even a computer as fast as ours cannot calculate the sounds in 'real' time. An intermediate stage has thus to be introduced, which involves a wait perhaps of several minutes whilst the computer calculates the numerical sequences which will constitute the final sound, and stores them in order on disk for subsequent conversion.

In the earlier pioneering days when composers had to wait perhaps overnight to obtain the results of a single program run on a central computer, it was doubtful whether the ends justified the means. In our situation, with a dedicated machine of our own, experience is showing that the relatively short delay is a price worth paying for the benefits to be derived, especially in avant garde composition. At present our system lacks such aids as interactive graphics, and auxiliary input devices such as keyboards and joysticks. We expect, however, to add these facilities within the near future as part of our continuing programme of research and development.

Course Work



Access to the Durham studio of necessity has to be restricted in the first instance to our own undergraduates, postgraduates, and members of staff, although occasionally we are able to allocate time to advanced composers from outside. Our undergraduate music degree course demands the usual combination of A levels at high enough grades, although it is not always realised that a combination of science + music is as acceptable as arts + music. A subsidiary subject must be studied during the first year, and the choice includes fields such as computing, electronics, or mathematics. Opportunities exist in our honours course to study both the theory and practice of electronic music, and also related topics such as musical acoustics. Composers may submit an electronic work as part of their degree. At a postgraduate level our one year foundation course pursues more advanced aspects of composition, both traditional and electronic, and prepares the more able student for a further two years of study, leading to a Ph.D.

The existence of our studio influences the concert giving scene, and during the academic year a number of concerts of electronic and other avant garde music are given to which the public are welcomed. Regional interest is fostered further by links with Spectro Arts Workshop in Newcastle, who provide studio facilities and stage concerts as an arts centre activity, and the relatively new Newcastle University studio just up the road.

Dr. Peter Manning is the Senior Experimental Officer in Music at Durham University, currently working on a book of electronic and computer music, to be published by O.U.P. in mid 1984. Along with Hugh Davies of Goldsmith's College, he is completing the entries for electronic and computer music instruments for a forthcoming dictionary of musical instruments, to be published by Grove in the new year.

For further information about the courses contact: Dr. Peter Manning, University of Durham, (Contact Details).



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Which Micro?

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Decillionix DX-1


Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.

 

Electronics & Music Maker - Dec 1983

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Computer Musician

Feature by Peter Manning

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> Which Micro?

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