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Chromascope Video Synthesiser

Article from Electronics & Music Maker, September 1981


The professional chromascope.


As one of the great megalomaniacs of the past, Scriabin was probably the first composer to inflict some highly dubious ideas of marrying music with the other sensations on a hitherto unsuspecting public. Like those that delve into the Soho backstreets, Scriabin never had enough, and is quoted as saying: "You will live in this music with all sensations, harmony of sounds, of colours, of fragrances". His 'Prometheus, The Poem of Fire' included a concertante part for a colour organ, or "clavier a lumieres", which played colours according to notes played on the keyboard. Attempts by psychologists and others to ascribe particular pitches, keys or timbres to particular colours haven't exactly made much sense, and it's generally recognised that synaesthetic experiences, or the way one sensory input (such as music) conjures up the impression of another sensation (such as colours or smell), is best left up to the individual listener to sort out to his own subjective convenience. However, for the enterprising contemporary artist wishing to indulge in his own interpretation of a son et lumière experience, a system capable of video synthesis could be a rather exciting idea. Unfortunately, it's often rather difficult to avoid commonplace associations such as green and orange with the consecutive fifths of Vaughan Williams in his most pastoral mood, or red with the stabbing string glissandi of the shower scene in 'Psycho'!

Background and Design



Units for translating sound into light have been around for some years, but the standard technique of using band-pass filters to trigger triacs leaves a lot to be desired in terms of subtlety. The Chromascope moves this potential for visual titillation well into the Eighties, though it doesn't exactly fullfil all the promises of true visual synthesis. Some background first: the Chromascope is the brain-child of Robin Palmer and it's his company, CEL Electronics, that launched the "Chroma-Chime", the first microprocessor musical door chime, in 1977. The Chromascope has been in development for the past six years, partly as a result of waiting for necessary advancements in chip technology, and partly to ensure that the market-place was in a suitably receptive state. As the video business is in a somewhat uncertain interim state between video tape and video disc technology, I'd say that they've chosen their launch time rather astutely, but a product like this is likely to sink or swim on the basis of long-term adaptability rather than its immediate appeal.

Currently, there are two versions of the Chromascope: the first is a domestic version priced at £295 inclusive of VAT; the second is a professional unit priced at £675 inclusive of VAT. Both units offer the same basic video synthesis features but with important distinctions that we'll come to later.

There are two modes for the operation of both units: either it can operate without an audio input, in which case all the colours and shapes are determined on a time cycle basis, or else it can work in the audio mode where some of the timers are put out of action and substituted with bandpass filters for very basic frequency analysis of the audio input. Like earlier, simpler units, four band-pass filters are used to analyse bass, low and high mid-range, and the treble components of the audio spectrum.

There is a mixture of digital and analogue circuitry to provide the best of both worlds. Apparently, if you use digital pattern synthesis, you're limited to rectangular forms, whereas analogue techniques give you nice wholesome circular shapes (the Lissajous figures). Basically, the unit operates by using a large number of synchronised function generators which produce all sorts of different waveforms. These are selected on a random basis, intermixed together, and, in some cases, with long and short feedback loops introduced on a random basis, then processed and fitted into a colour matrix.

Black and White photograph of colour-enhanced Video input.

An audio input has the effect of modulating a random picture, so that, instead of sequences and colours moving under the control of internal timers, these are at least partially controlled by the outputs of the four band-pass filters. Also, as a separate function, the sequencing, i.e., the change from one pattern to another, can be controlled by the bass rhythm derived from the music. Because music is so complicated, Robin Palmer suggests that it doesn't make sense to translate fast pitch and dynamic changes into visual terms. I'd agree with this point of view if the Chromascope offered a viable alternative; instead the viewer is obliged to view the product of internal programming with only (it seemed to me) a minimal interaction with the audio input. The main problem lies in the saturation of the senses that a constantly and randomly changing pattern of colours engenders. I tried concentrating on a display demonstrating a Genesis-modulated product of the Chromascope, but just ended up with a headache and a confused visual cortex; after all, of such stuff are brain-washing techniques made!

I'd like to see a video synthesiser offering the visual equivalent of additive synthesis of sound by actually building up patterns on the basis of the frequency structure of the music rather than by internal function generators more-or-less randomly intermixing. One of the most captivating visual displays that I've ever seen used fifteen or so band-pass filters to derive control voltages from an audio input; these were then patched to synthesise concentric colour rings, the pattern synthesis following a progression from dark 'bass' rings in the centre to light 'treble' rings at the edge.

The domestic chromascope.


Controls and Other Options



If the music interpretive qualities of the Chromascope leave a lot to be desired, other areas of the unit compensate for this, at least in part. Whereas the domestic version is limited to either the free-running sequencer mode, with timing of sequences selected by front panel controls, or the audio mode, with some elements of timing derived from the music itself, the professional model includes some very interesting facilities for processing external video inputs.

This version accepts visual sources such as a VTR or camera, and a cross-fade control allows patterns and colours to be superimposed on the visual source material. This is also true for a monochrome input and the colourising is really very impressive. At the demonstration I attended, the unit was being used in conjunction with a VTR playing 'Yellow Submarine'; the results can only be described as hyper-psychedelic, and, even though this could be regarded as an attempt to gild the lily, it does demonstrate that the use of the Chromascope, to superimpose abstract patterns of colours on familiarly-structured material, offers much scope for video studios and those amongst us with a Kenny Everett mentality. It's encouraging to see a British manufacturer producing a product that looks so thoroughly well-engineered; in fact rather Japanese in appearance! However, I suspect that the pricing of these units is likely to put the Chromascope out of reach of all but 'the man who has everything'. I, for one (but not one), wouldn't gain much more than transient amusement from the domestic model; for half the price maybe I wouldn't mind so much.

Availability: directly from the manufacturers, CEL Electronics, (Contact Details).



Previous Article in this issue

One-Handed Guitar

Next article in this issue

The Linn LM-1 Drum Computer


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

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Electronics & Music Maker - Sep 1981

Gear in this article:

Video FX > CEL Electronics > Chromascope

Review by David Ellis

Previous article in this issue:

> One-Handed Guitar

Next article in this issue:

> The Linn LM-1 Drum Computer


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