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Pitch to voltage converters and envelope followers are conventionally those synthesiser peripherals that attract little interest from most musicians, possibly because the average synthesist and synthesiser manufacturer is more concerned with trying to extract the maximum information from the way the keyboard is played than considering any other type of human input. Moving away from this restricted point of view, there's obviously great potential in providing an interface between the sounds of the instrument, with the human input that initiates it, and a synthesiser to reinterpret the original musical intentions. A number of manufacturers, Gentle Electric, for instance, make very good pitch to voltage converters that will more or less faithfully track any pitched information fed into it from voice or instrument, and then produce a control voltage with which to control a chosen synthesiser. This sounds fine in theory, but many musicians that aren't suckled on synthesisers find problems in relating their technique to an electronic instrument that needs a considerable amount of knob-pushing to get anything interesting or useful out of it. I wouldn't be surprised if this explains the rather chequered career of guitar synthesisers and the like.

So, the first step that Musico have taken with their Resynator is to integrate a synthesiser section within the same package as the interface and then normalise the functions of the synthesiser so that it is totally geared towards the performing musician wishing to expand his instrumental horizons without subverting his technique to the potentially (for him, at least) dehumanising demands of synthesisers.

Pitch to voltage conversion can be effected by a variety of means, including the use of a phase-locked loop which locks onto an input frequency and adjusts an internal VCO until the frequency difference is nulled. The voltage necessary to do this can be sampled and then used as a control voltage for a synthesiser, but the limitations imposed on the sampling technique and rate invariably lead to mistracking of the input frequency.

Musico go way beyond this level of technology by using a Digital Frequency Analyser that converts pitch to bits of digital information at a fast but variable sampling rate for processing by a microprocessor. Sampling of the input occurs every 40 microseconds, which results in very accurate pitch tracking. I couldn't ascertain what routines were being used to process the pitch data, but I presume that a clean-up operation is performed, the fundamental pitch being sorted out from overtones. The digital data from the CPU is then converted to an analogue control voltage with which a principal VCO, offering sawtooth, square or variable pulse waveforms, is controlled, in addition to a second VCO, called a 'FXO' (effects oscillator), which can be configured to provide harmonising, phase-synching, or various types of overtone synthesis as a result of being modulated by the principal VCO.

An excellent facility that the Resonator possesses is the ability to set the tuning relationship between the two VCOs by merely pressing a foot-switch and playing a note which is then compared to an internal A440 reference, the FXO then being automatically returned to the new interval.

A standard analogue envelope follower, patched to a VCA, tracks the dynamics of the input signal pretty accurately as far as I could tell from the demonstration I heard using guitar and voice input. An important feature is that decay time follows the input signal unless it's overriden by using a footswitch.

So far, we've covered the pitch and envelope analysis performed by the Resynator; what about timbral considerations? It's here that I feel that Musico haven't gone far enough. Practically everyone must have heard the products of analysis of voice formants in the shape of that pie in the blue sky, the vocoder. In analogue terms, this involves a lot of bandpass filters and envelope followers and is usually pretty limited in terms of sampling accuracy. Digital frequency analysers, on the other hand, produce some fairly remarkable results when applied as vocoders, as evinced from work being currently carried out at Stanford University in the States. I'd have thought that it would be valuable to use the DFA in the Resynator for VCF control by using the processor to analyse harmonic or timbral information. This doesn't mean that one is forced to copy the input signal faithfully; instead, really interesting and potentially useful sounds could be derived from digitally cross-patching the results of timbral analysis, i.e., low harmonics could trigger a high filter sweep and high harmonics a low filter sweep.

What Musico do use, though, is a VCF that can be patched to eight different 'filter envelopes' ("Select a Shape" in the photo).

The filter envelopes consist of a variety of more or less complex filter sweeps initiated by respective stepped control voltage patterns stored in ROM and controlled by a second microprocessor. Musico call this their 'Timbral Image Modulator', and it is very effective in animating the output of the synthesiser in a way that's far less predictable and infinitely more interesting than most filter sweeps. The idea isn't unique, though, as the Phase-filter produced by Blacet Music Research in the States uses the same principle: in their case a 14-step variable digital waveform generator controls a Curtis Electro-Music VCF chip to shape the frequency content of a signal fed into it. To sum up: the Resynator tracks a variety of input sources with terrific accuracy, though I haven't heard its performance with signals of high transient content or ultra-rapid pitch variation, but it is strictly a monophonic device and makes no attempt to perform any timbral analysis on the input signal, which, it seems to me, is a serious omission considering that its main selling point is the digital frequency analyser. As a live performance addition its range of footswitch controls and easily-comprehended panel controls must make it a very attractive proposition to the musician normally scared-off by synthesisers. To my ears, the basic sound isn't wildly different to that from other quality monophonic synthesisers controlled by an external input, and for a UK price of approximately £1,200 it is very expensive.

The Musico Resynator is distributed solely by Syco Systems, (Contact Details).