Strumenti Musicali: Sintetizzatore Chroma
By Francesco ChiariniA review from the Italian magazine Strumenti Musicali, January 1983. Thanks to Odysséas Tsakas-Grigoriadis [21010242] for the article scan, and to Enrico Dibennardo [21030494] and Luca Sasdelli [21010226] for the English translation.
His name is Chroma, a polyphonic synthesizer based on analog-digital hybrid technology with touch sensitivity. Designed in the ARP factory and manufactured by Rhodes, it will certainly be competitive with the few musical computers currently available on the Italian market.
The Chroma is targetted to Musicians with capital "M" (to be clear, those using two hands when playing), and for this reason—if we exclude its 25-pin external computer interface—isn't designed to be driven by sequencers or external rhythm units.
A choice like this distinguishes the Chroma from its major competitors (OB-Xa, Prophet) which are generally equipped with a computer interface but are missing a touch-sensitive keyboard, and makes it closer to the old and proud Yamaha CS-80. From first listening, the exceptional dynamics of the Chroma are in evidence, due to keyboard sensitivity, obtained by dedicating a microprocessor to key velocity calculations. The Chroma adds huge live-usage versatility to a variety of timbre never before heard on analog polyphonic systems.
Let's consider the two circumstances in which the Chroma can be used: performance and programming.
The Performance
There are two distinct ways of using the Chroma: performance and programming. This doesn't mean that it cannot be played while programming (or vice versa) but that, before going live or into the studio, one should think about how to approach the machine.
It it often the case that the person playing a polyphonic synth isn't the same person who programs it and—with some exceptions—it's reasonable to assume that a keyboardist, after dedicating several hours a day to piano exercises, wouldn't have enough spare time to dedicate him or herself to electronic sound synthesis, of the sort which audio engineers are used to. This dual role of electronic musical instruments (which will hopefully soon disappear) is today much more clear and more obvious in the Chroma than in other polyphonic synths. This not because timbre programming is particularly complicated (actually less so than most musical computers), but because the Chroma has been designed to help the musician to (almost) never take his or her hands off the keyboard, while having several expressive controls at the fingertips.
A look at the panel immediately reveals the paternity of the Chroma: the appearance is similar to that of the ARP Piano. Five sliders and around 70 soft-touch switches allows one to recall and edit fifty different timbres. With respect to expression control, to the left of the keyboard there are two spring-loaded wheels [sic] which can be programmed to control multiple effects (usually Pitch Bend and Vibrato depth); the Chroma is supplied with three pedals, two of them programmable (usually the sustain on right and the soft damper on left). The third footswitch, very useful in live context, allows one to switch timbres without need to use the panel switches; it's possible to program a sound's sequence, press the footswitch and swap from a choir to a grand piano without removing a finger from the keyboard. The split function is excellent: the keyboard split point can be set at any key, and any patch can be assigned to either of the two zones, or even the same patch to both as each part can independently be transposed one octave up or down.
A series of buttons allows storage and recall all 50 patches from tape. There are eight outputs: two studio balanced connectors (XLR 600 ohms), two mono ts jacks (high and lo impedance), and four assignable trs jacks, which can be used either as individual voice outputs or as send/return paths.
Editing
Besides the microprocessor controlling the keyboard, the Chroma incorporates a second one for voice managing and storing parameters. Editing on the Chroma is rather simple although you must become familiar with the instrument and have the manual, with its useful tips, within reach; some of the switches may represent up to 16 different functions and it may be very difficult to remember all the numeric values needed to access the various functions. The global editing of the instrument can be achieved through a single slider labelled "parameter control" used to set the numeric codes, and the 50 membrane switches which are normally used to access the patches before having pressed the "param select" switch which turns the patch membrane switches into voice parameters.
Pressing "prog select" you can access the play mode again. All voice parameter editing and data settings are really very simple in the end.
It is impossible to provide an exact idea of the timbric potential of the Chroma; suffice to say that besides the classical "VCO-VCF-VCA" chain with two envelopes (X 16 voices or 2 X 8 voices in split mode) there are still 15 more synthesis techniques available, such as: frequency modulation of the filters (VCF FM), amplitude modulation (VCA M), various ring modulators, filters cascades and more (see Figure 1).
Figure 1: Looking at the block diagrams that accompany the instrument, reproduced here, can give us an idea of the flexibility of the Chroma system.
Touch sensitivity is obtained through the envelopes which are digital, of the APSR type, where "P" stands for peak: in other words the maximum amplitude level is proportional to the key velocity applied to the keyboard (see Figure 2).
Figure 2
The only programmable performing patterns are a series of arpeggios and a monophonic sequencer capable of 195 notes. Accurate tuning is achieved through a self diagnostic routine which tunes the oscillators to the clock reference frequency of the microprocessors.
Conclusion
The Chroma, with its great and rich sound, great dynamic range and great ease of use in the live environment, can be considered the king of the polyphonic hybrid analog/digital synthesizers.
Probably within a decade or so it will be remembered as the "swan-song" of the hybrid synthesizers: a swan with an outstanding voice. 