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Article from Electronics & Music Maker, February 1984


This column offers readers the opportunity of standing on the soapbox and airing their views on micros and music. This month, John Yau, a third-year student at Heriot-Watt University, casts a few aspersions on the musicality of micros and their manufacturers, and talks about the hardware projects that he's developing around the BBC Micro. We've invited him to submit this to Computer Musician as a possible project, so watch this space...

"As well as having a personal interest in micro-based music, I am currently developing a BBC Micro music synthesis system for my final year project at Heriot-Watt University. Electronic music and micros are both fast-moving growth areas in the consumer electronics industry in their own right, but when you put them together, you've got something which may well 'explode' within the next few years. With respect to the latter, I'm glad that there are mags like E&MM which keep us informed of the latest state-of-the-art developments.

I feel that there is a definite place for micros in music synthesis. Without being too specific at the moment, the keyword is 'control'. The present generation of micros are unsuitable for direct synthesis of waveforms because of limitations of speed. The key to the potential music capability of a micro lies with both its programmability and its hardware. The programmability offered by a microcomputer opens up tremendous possibilities for the micro musician, but contrary to what advertising copy says about a particular micro being capable of all the sounds of the orchestra, there's no micro that's adequate as a self-contained music synthesis system. So, hardware external to the computer has to be developed, and this requirement falls hard on the average micro owner.

The average consumer believes that with a suitable software package, perhaps the cassette with the gloriously glossy inlay on their local WH Smiths' shelf, he or she can relax to a little Bach or Vivaldi. Unfortunately, no matter how manufacturers boast about the number of channels and octaves, the sound chips used in current micros are not well suited to music. They were designed with game sound-effects in mind and lack timbre variation and frequency and amplitude resolution. In addition to that, the sound chip is often sited in a sea of highspeed digital signals which doesn't help the S/N ratio much - unless you want to compose 'The Breakfast Baroque Plus Frying Eggs'...

The BBC Micro has done well in overcoming the limitations of its sound chip by utilising routines in the Operating System to generate software ADSR envelopes. But with only 16 levels of amplitude available, it's a rather bumpy ride for slow attacks and decays. On top of the unremitting square waves, the 10-bit frequency resolution is the final blow - as frequency increases, the tuning ranges from bad (for the tone deaf) to AARGH!

Despite their inherent limitations, these sound chips still have uses if you're interested in the educational side of things. However, a line has to be drawn between the serious music punters (those who normally play instruments, etc.) and people like little Johnny and Dad, who marvel at the rendition of 'Greensleeves' buzzing out from their latest purchase. Unfortunately, and perhaps understandably, the micro manufacturers (and most reviewers) don't seem to recognise this line. As a result, it is difficult for the layman to distinguish between genuine claims and pure sales hype.

BBC Hardware



As I mentioned earlier, the real value of the micro is its programmability for controlling external hardware. At the moment, hardware add-ons are the inevitable way out for the more serious musician. After all, you don't buy a £400 BBC Micro to listen to some square waves coming out of a thimble-sized speaker. I know the expense of add-ons makes them forbidden territory for many readers, but I'm sure that manufacturers will produce kits or even finished items to ease the financial burden in time.

To illustrate my ideas on this front, let me describe the system I'm working on. The system currently under development comprises the following hardware:

1 A percussion board connected to the user port of the BBC Micro.

2 Four 8253s and an 8255 interfaced to the 1 MHz bus provide 6 voices (2 oscillators per voice). The voices also have a sub-octave to give the same sort of sound as in string synths and organs. An arrangement with the 8255 similar to the OMDAC generates the trigger voltages. Dynamics are possible since the volume of a note depends on the size of the trigger voltage. The tones go to an envelope generator and filter board (again, just like organs and string synths). We therefore have a 6-voice string synth interfaced to the BBC Micro, but as the filter voicing is under the micro's control, realtime processing is possible.

3 A single digital voice card, again under complete control of the BBC Micro. The card uses conventional TTL, so the chip count is high (18). The 2K x 8 CMOS RAMs can be addressed by the micro so that waveform tables can be filled. The static waveform then goes to a CEM 3372 (3 VCAs, 1 VCF), which is controlled from the remaining channels of the OMDAC-like configuration. In effect, this gives us a hybrid synthesiser, with all its parameters under micro control. The RAM address lines address two separate 2K RAMs, which go through separate 8-bit DACs, and then to two of the CEM 3372 VCAs. The idea is that with a clever bit of software the CVs for the VCAs can be made to pan during a note in such a way that the timbre will consist of smooth sequencing through 16 waveform tables. On top of that, there's also the possibility of VCF sweeping and so on.

Software



Of course, all the above hardware will be useless without software. The software I'm working on at the moment is in the form of an interrupt-driven interpreter, using the two VIAs on the BBC, which takes its code from an MCL sort of file. The main emphasis is on a non-real-time system, but sufficient provision is made for the (inevitable) possibility of extending it to a real-time system with keyboard.

I chose to utilise non-real-time because I want to have a system which does not have the glaring faults of many commercial products. For instance, the whole idea behind using a micro is its power in control and programmability, yet systems like the Compu-Music, Mountain Computer Music System, and Apple Chroma software do no allow you to program in repeats, macros, del capo, del signe el fine, and so on. The ultimate aim of the software is primarily as an accompaniment score machine, providing bass, chords, arpeggios, and polyphonic sequencing, not to mention the drums. Its other potential use is to play a complete musical score with a distinct improvement over the performance of the standard sound chip.

As you can see, it is a very elaborate system. The hardware costs may be quite high (£200), but this sort of modular project can be broken down. In fact, the drum board could be knocked up for just £10, allowing you and the Beeb access to drum scores that only the most sophisticated drum machines can produce. Alternatively, an analogue synthesist may be more interested in exploring digital synthesis with the digital sound card."



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Rumblings

Next article in this issue

Studio Scene


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

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Electronics & Music Maker - Feb 1984

Computer Musician

Topic:

Computing


Feedback by John Yau

Previous article in this issue:

> Rumblings

Next article in this issue:

> Studio Scene


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