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Wednesday, October 23, 2013

Rhodes Chroma

Analogue Polysynth (Retro)


Reviews : Keyboard

NORMAN FAY takes a retro look at the Rhodes Chroma, the last and most obscure of ARP's long line of analogue synthesizers.

When I first saw a Chroma, back in 1982, it had been delivered to my local music shop along with a consignment of Memorymoogs. The newly-released Moog was a 'hot item', and people in the shop were actually queuing up to play one. Nobody played on the Chroma -- to a generation of synthesists raised on knobs, switches and sliders, the Chroma's flat control panel and weird, clunky piano keyboard were too intimidating. The poor old Memorymoog (super though it is) was almost the last instrument of its kind, while the Chroma was a glimpse into the future, with its velocity-sensitive keyboard, pre-MIDI computer interface, multitimbral sound facilities, its availability as a keyboardless 'expander' unit, and (worse luck) its digital parameter access controls. One day all synthesizers would be made this way!




The Chroma is a hybrid analogue/digital polysynth. The oscillators, filters, and amplifiers are analogue circuits, whilst the LFO and envelope generator control voltages are digitally generated. Its 'variable architecture' lets you assign the oscillators, filters, and amplifiers in different ways, making it almost as versatile (and confusing for the unwary) as a small, modular system.

The easiest way to explain how this variable architecture works is to compare it to Single or Double modes on a Korg M1: Single mode on the M1 is the same as Patch 1 on the Chroma. You get one VCO, one VCF, one VCA, one LFO, and two envelope generators. In this mode both instruments are 16-note polyphonic. If you switch to Double mode on the M1, equivalent to Patch 2 on the Chroma, then you double your synthesis power at the expense of halving your polyphony. A further 13 patches are available, with the filters arranged in parallel, in series, or in 'variable mix' mode.

VCO B's frequency can sync to that of VCO A, for a variety of powerful cutting timbres, or you can include a ring modulator. Best of all is 'filter FM', which is selectable in all bar one of the basic patch types. Here, VCF A is modulated at audio frequency by VCO B. This produces fantastic but very controllable effects, quite unlike anything else I have ever heard.

This versatility is matched in the Chroma's modulation options, where nothing seems to be preset. There is no 'filter envelope generator', for example. You can choose any, or indeed several, of the four available. Want to use a different envelope for each VCF? No problem. A different LFO for each oscillator? VCO pulse width controlled by keyboard position? Easy!
The synthesis possibilities are almost endless, as are the possibilities for getting lost. Most of the Chroma's circuits have 'something extra' when compared with its contemporaries. The LFOs, for example, have no less than 16 waveforms, including six different stepped waves. They are also polyphonic, which means that chordal sounds are very spacious and full. Each oscillator, as well as having the usual variable pulse waveform, also has a variable sawtooth wave. Each VCO has its own portamento control, so they can be set at different rates -- very effective for both lead and chordal effects.

This depth of control is the key to the Chroma's sound -- detailed, wide, airy and rather beautiful. Though it lacks the power of a Memorymoog or a Roland Jupiter 8, the Chroma also lacks the 'muddiness' which seems to go along with that kind of analogue power. Having owned one of these splendid instruments for eight years, I have found that its only weak area is the production of deep bass sounds, which have evaded me thus far. Its greatest strength lies in the way both lead and chord sounds sit clearly in a mix, without dominating it. With its dual filters, a variety of unusual yet very musical sounds can, with patience, be programmed. Convincing vocal sounds are a speciality thanks to these filters, as both fixed and keyboard-tracking resonant peaks can be placed within the sound.

The Chroma is also very good at 'imitative' synthesis, and the intrepid synthesist is helped here by the excellent velocity-sensitive keyboard, which (when functioning) is one of the nicest I've ever encountered, in terms of playability. It's a non-sprung, weighted design which seems to be an almost perfect balance between organ and piano type feels. It was one of the first velocity-sensitive designs available, along with the Yamaha CS80. An upgrade was planned to give the Chroma polyphonic pressure sensitivity, but I don't think it ever materialised. (If any readers know different, then please let me know!)




The instrument has a large, flat top, designed for another keyboard or a computer and monitor. It also has a fine range of controls for expressive playing, including two footpedals, whose functions can be programmed as part of each sound.

Back in 1982, the most futuristic features of the Chroma were the fact that the instrument is multitimbral, and the 'TRIAD' computer interface. When plugged into an Apple II computer fitted with the correct hardware, this acted much like today's MIDI interface. Such features are now taken for granted, but back then the ability to edit your sounds from a computer screen, or replay sequenced parts from a computer, with program changes and so on being recalled, was almost unthinkable. Thanks to this interface, adding MIDI capabilities to a Chroma is very simple (see 'MIDI-fying The Chroma' box).




Some of you may already be rushing out to find an example of this wonderful synthesize, but hold on... My Chroma, which has never been regularly gigged in all the time I've owned it, has cost me about £100 a year in repair bills. The main problem seems to be the dual voice cards inside the instrument, which go out of tune. Fortunately, when this happens, the instrument's software will switch off the offending voice, so that you can continue playing. In fact, my Chroma is currently functioning as a 7-voice polysynth as I write! This is easy enough to fix -- all you need is the service manual and an oscilloscope.

Occasionally something worse goes wrong with a voice board. I've had to replace a special chip on two of mine, a part which is no longer manufactured. It took six months to source one last time, which rather depressingly leads me to conclude that, eventually, my Chroma will become unserviceable, unless an alternative part can be found.

Reliability-wise, the Chroma is no worse than many instruments of its time. This is inevitable, I suppose, given that microprocessor-controlled synthesizers were a new concept back then. So if you're looking for an analogue synth to play at gigs, forget the Chroma and look for a more reliable and portable Japanese instrument. I'd also forget about the Chroma if you're making techno music, since the Chroma only has one parameter slider and is thus not much use for real-time analogue fiddling, and the instrument doesn't have a spectacular bass-end. Otherwise, if you're looking for a fine analogue synth for your studio, then the Chroma is well worth considering.




Despite the fact that it is an ARP design, the Rhodes Chroma is relatively obscure today. This, and the fact that the Chroma isn't well endowed with knobs and switches, means that an example can be picked up far cheaper than its contemporaries. A good deal then, provided you can find one. The problem is that most Chroma owners are very attached to them. If you just want to dabble with subtractive synthesis, then you'd probably find other, simpler analogue synths more instantly rewarding. On the other hand, if you love programming and playing synthesizers, and want something with a lot of depth from which you won't easily tire, then the quality of this instrument will be remembered long after the expense is forgotten.

Published in SOS October 1995

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