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Sonics: Rhodes Chroma Synthesizer: The Creative Touch

By George Faithfull

The following article is from the June 1983 issue of the Australian magazine Sonics. I received a photocopy of the article when I bought my Chroma. I made numerous attempts to track down the magazine for permission to post the review on this site; as far as I can determine, Sonics no longer exists, and there is no trace of what happened to it or who might currently own rights. If you have any information, please contact me. I have omitted two photographs from the article, which are very poor quality in my photocopy. They are of the back panel and case--the earlier versions, from the brochure.

The range of synthesizers on the market today is constantly growing. It has got to the stage where new keyboards are being superseded even before they hit the shops. This is due both to technological advances, and to manufacturers' trying to outdo each other, either by simplifying and cost-cutting, or by providing a plethora of extras to attract the eye of the confused consumer. "Not only does it have 87 VCAs, each with an overhead cam ultra-drive, but it can wash twelve pounds of woolies in under a minute--even in cold water!"

One possible solution is to provide a keyboard that can do all that a new keyboard player might require, along with the potential to upgrade as new developments occur. Such a machine is the Rhodes Chroma.

First and foremost, I will say that the recommended price is [Australian] $7650, but let me quickly add that not only does it do everything a fully-fledged (or novice) synthesizer player might wish for, but it is both software updatable and provides for interfacing with other hardware such as Apple II and TRS 80 computers. "SO WHAT?" I hear you mutter. All I can say in response is, "Read on!"

THE CHROMA at first appears less stream-lined than its predecessor, the ARP Quadra. In fact it looks quite chunky in comparison. It is also unusual in that most of the control switches are touch-sensitive, lying flush with the panel. The trim is real wood, and even more surprisingly, so are the keys, of which there are 64. The dimensions of the whole are 107 x 61 x 15 cm, and it weighs in at 32 kg. Included free is an ATA Anvil road-case, probably around $400 worth, which takes the total weight to around 58 kg. Other freebies include a dual footswitch assembly, a volume footpedal, an on/off footswitch, a cassette interface cord, a cassette of 150 pre-programmed sounds, and not one but two instruction manuals.

The keyboard itself is velocity-sensitive, with eight levels of sensitivity, and an optional pressure-sensitive adaption (i.e. control by 'aftertouch' pressure) will soon be available (for around $400). The touch is very good, approximating that of the Yamaha GS2, and quite unexpected on a synthesizer. This is due to the wooden piano-keys, each centre-mounted, and precisely balanced and weighted to achieve an acoustic piano-like feel.


Velocity-sensitivity in the Chroma: Each key operates a leaf switch. Basically, when you press a key, it moves a metal blade from the lower post to the upper. The switch, which is controlled by a separate microprocessor, measures the time of flight of the blade and communicates that value to the Chroma's microprocessor. The result is true dynamic control over each note.



The Chroma can store fifty sounds at a time. These fifty sounds can be loaded or dumped, all at once or one at a time, via a cassette interface. The sounds (or programs) are stored in a memory powered by two size AA batteries.

As usual, many of the sounds provided by the manufacturer can be improved on in some way, especially since American sounds tend to be a bit on the 'funky' side. However, there are some very impressive and realistic programs among the hundred and fifty on tape. The harp, Renaissance flute, cathedral organ, jazz guitar, Farfisa organ, cello, acoustic jazz bass and pizzicato violin are all excellent. The velocity-sensitivity of the keyboard seemed to bring out the dynamics of the bass, strings, clavinet and harpsichord, and allowed a great degree of control. This was especially noticeable on listening to a tape of orchestral and instrumental compositions, recorded entirely using the Chroma by Chris Harriott. Chris composed the music for the hit musical Dingo Girl which enjoyed considerable success in Sydney recently, and he is a talented film-score and jingle composer with his own 8-track studio. He has owned a Chroma since the end of 1982 and it was his that was used for this review. Among his personal sounds are an exact string program, a Fender Rhodes piano, and a male-voice choir, all of which demonstrate that the Chroma is capable of a great deal.


The front panel of the Chroma is neatly set out (perhaps a little too neatly--neatness can sometimes lead to identification confusion when it comes to quick on-stage decisions). On the far left are sliders for master tuning, equalisation (bass, middle and treble) and overall volume. Next to these are sets of control functions. One set controls the linkage of two programs, allowing either a 'dual' linkage or a 'split' linkage, with the linked program able to be above or below the split. The split itself is programmable anywhere on the keyboard. Another set of control switches transposes the selected program up or down one octave, and if a particular program is in linkage with another, the other program can be separately transposed up or down also. Interestingly enough, the transposition does not affect notes while they are being held--only when they are released. This enables a chord to remain unchanged while subsequent notes played around it are transposed. The other control functions are the cassette interface switches, automatic tuning, storage of manually set up sounds, and the editing of selected programs.

The touch-sensitive switches on the right side of the panel have two major functions each. Firstly, they act to select programs 1-50(the stored pre-set sounds), when the Program Select switch is activated. Secondly, they call up fifty different parameters which are the individual pieces of information that go to make up a program. The latter function is selected by the Parameter Select switch. Program numbers, when selected, are displayed in a large two-digit display. Parameter numbers are displayed in the Data Readout display, just beneath the Program Number display. The Data Readout display also shows the amount of the parameter used, and this amount is attained by moving the Parameter Control slider. Different parameters have different ranges of course, and the slider can operate by selecting from two positions up to 64 positions, depending on the parameter.

The touch-sensitive switching provides no feedback as to exactly what the controls are doing, so the Chroma's designers have thoughtfully provided a mechanical 'tapper' which audibly clicks under your fingers when you activate a switch or select the value of a parameter. If for example, a parameter has only two possible values, only one click will be felt and heard as you move the slider from one extreme to the other, whereas for a 64-value parameter, it will click through them all as the slider is moved. This tapper mechanism can be turned off if desired.

Outputs and Inputs

On the rear panel are inputs for the dual footswitch, volume pedal, on/off switch and one extra volume-type footpedal.

There are also four input/output jacks which can be used to send/receive certain effects by using stereo plugs from each effect (such as phaser, reverb etc). Any program can select a particular effect automatically if it has been so programmed using the Output Select parameter. This effect is then mixed into the output.

Output is possible in both stereo and mono. Mono mixes exit via an XLR or high/low jack outputs, and these mixes consist of the selected program, any other program linked to it, and any added effects. Stereo outputs are achieved by rerouting the linked program via, say, output 3, thus removing it from the mono mix and allowing it an output separate to the main program. Stereo outputs can also be XLR or jack.

The input marked 'sequence' is for an on/off switch which can trigger a change from one program to another. Each program can in turn be programmed to change to one other, and so by setting up a sequence (say 1-19-7-50-2-1) you can change right through those programs without touching the panel--obviously very valuable if your fingers can't leave the keyboard or you are playing another keyboard.

Finally the 25-pin computer interface allows you to connect two Chromas together and control them from one keyboard, or to link the instrument to an Apple II or TRS 80 computer. This will give expanded memory facilities and multi-tracking--enabling eight independently voiced channels and sequencing to occur, something only previously possible with an instrument like the Fairlight CMI, or the Passport Designs and alphaSyntauri systems mentioned elsewhere in this issue.

How it works

The Chroma is both analogue and digital. It has eight dual-channel circuit boards in the rear of the machine, each channel containing an oscillator, a waveshaper, a filter and an amplifier (i.e. 16 of each). This is the analogue section. The central computer, located under the front section of panelling, contains two microprocessors: one to control the touch-sensitive keyboard, and the other to control the oscillators, waveshapers, filters and amplifiers of the circuit boards via 32 envelopes (two per channel) and sixteen low frequency sweep signals that trigger and modulate the pure sounds in various ways. The central computer, of course, is digital.

Signals from various levers, pedals, the control panel and the keyboard itself are all processed via the central computer and are then relayed to the circuit board channels.


The programming facilities of the Chroma are seemingly endless, allowing more capabilities to be incorporated into one memorised program than virtually any other synthesizer. This is largely because the Chroma is digitally based, with all operating, programming and tone controls generated in software, leaving the sixteen oscillators, filters and amplifiers completely accessible. For example, when a two-VCO sound is created on a Prophet or a Jupiter 8, both VCOs must use the same two envelopes, but because the Chroma is virtually sixteen complete synthesizers, two-oscillator sounds have four envelopes and you can thus have quite complex sounds even before a program is linked with another.

Another important asset is the ability of the two channels on each of the dual circuit boards to be patched in a variety of configurations. They can be separated as sixteen independent channels to give sixteen-note polyphony (for single-oscillator sounds) or patched as eight independent channels, with two-pole filtering (high and low pass) and eight-note polyphony. Even further, the eight dual boards can be patched in parallel, series or other variations with four-pole filtering and four-note polyphony, creating very rich and complex sounds. Patched configurations can be used to synchronise the oscillators to each other, to allow ring modulation for metallic and bell sounds, and to create filter frequency modulation for phase-shifting, vocal effects, and percussive sounds.


1. Pitch

The Tune parameter tunes the unmodulated pitch to a normal keyboard range, or to play in quarter-tones or whatever you wish, even to the extent of reversing the keyboard so that low to high pitch goes right to left. The Pitch Modulation has a menu selection, i.e. sixteen possible ways of modulating the oscillator using the keyboard glide, the low frequency sweep generator, either of the envelopes, pedal 1 or 2, lever 1 or 2, the velocity-sensitive keyboard or the pressure-sensitive option. As there are three separate Pitch Modulation parameters, you can choose three of those sixteen types. Finally, there are three Modulation Depths to choose from: semi-tone, quarter-tone and sixteenth-tone increments, all three capable of modulating above or below the note.

2. Waveshape

There is a choice of four waveshapes--sawtooth, pulse, pink noise or white noise. The Pulse Width can be adjusted from no pulse at all to a very complex wave. The Pulse Modulation, like the Pitch Modulation, has a menu selection allowing one of sixteen types of control, and the depth of the Pulse Modulation has a large negative to positive range.

3. Cutoff

The Filter can be low or high pass, and there is a wide range of Resonance control. The Filter Tune doesn't necessarily track the keyboard unless it is modulated by the keyboard glide. Again, like the Pitch Modulation, the Filter Modulation allows three out of sixteen types of control, its depth being adjustable for all three choices in semi-tone increments.

4. Volume

The amplifier has two modulation inputs, each using a separate envelope and each Modulation Depth is adjustable from -30 to 0 dB. Post-modulation is controlled by a variety of things, including the keyboard (as a Keyboard Follow), the sweep (for a tremelo effect), and pedals 1 and 2.

5. Glide

This can be chosen as Portamento (smooth) or Glissando (chromatic), and the Rate is adjustable over a large range.

6. Sweep

The low frequency sweep generator modulates the pitch (vibrato, trills), the waveform (pulse width modulation), the filer (tremolo) and the amplifier. It can be independent, key-following or free-running. Sweep Rate is adjustable, and both the Sweep Rate Modulation and Sweep Amplitude Modulation are controlled with a sixteen-type menu selector. There are sixteen Sweep Waveshapes to choose from, including sine, triangle and sawtooth.

7. Envelopes

Both envelopes can be programmed with Amplitude Touch, which sets the envelope peak as a function of keyboard velocity. This is invaluable for, say, string sounds where fast-hit notes have a sudden attack whereas slow-hit notes have a smooth entry. Attack, Decay and Release times are adjustable from 0 to 10 seconds, with the possibility of an Extra Threshold Release triggered by the velocity at which the key is released. Attack and Decay Modulations have menu selections and a Delay parameter (on envelope 2 only) can delay that envelope or cause the sweep generator to trigger envelope 2 at the beginning of each sweep cycle.

Other control parameters

The Detune between dual-oscillator setups allow chorusing effects and the tuning of ring-modulation programs.

The Footswitch Mode assigns eight possible combinations of duties to the dual footswitch, which is especially useful when set differently for two linked programs. The Keyboard Algorithm defines the way in which the Chroma assigns synthesizer channels to notes, which gives you amazing versatility for things such as chord-gliding, triggering chords which don't play until a footswitch is depressed (allowing cuing while playing another keyboard), arpeggiation in any direction, and most importantly--sequencing. The notes played when sequencing are remembered in order, up to 195 notes, and the sequence keeps playing as long as the sustain pedal or a key is held. New notes can constantly be added, and by means of the velocity-sensitive keyboard, the dynamics of every note in the sequence are remembered, exactly the way they were played. Sequencer timing can also be programmed accurately so that you can link two sequences together or to an outside drum machine.

Self Diagnostics

By using the Set Split switch in combination with certain numbered switches, the Chroma can give diagnostic feedback on itself. These diagnostic functions include locating and displaying a malfunctioning circuit board, disabling any malfunctioning circuit board, turning the tappers on and off, muting the oscillators, testing the LEDs and even checking the memory batteries (with an actual voltage readout!).


In conclusion, I can only say that this is a superior machine. Not only does it give you the ability to play a synthesiser dynamically, but the programmable facilities make live performance much easier in many ways. Although seeming complicated, it is pretty well instantly playable, and some time later, after a journey through the programming manual, its vast potential begins to become evident. The size and weight are a drawback in comparison to a Jupiter 8, say, but you do get a free flight case.

Computer linkage is already available; the central computer located under the front panel can be updated without touching the basic sixteen synthesizers; and the front panel itself can be peeled off and replaced with any necessary replacement panel. Damaged or malfunctioning dual-channel circuit boards are instantly replaceable from your dealer, so that you don't have to be forced off the road in an emergency.

I thoroughly recommend the Rhodes Chroma to any keyboard player looking for the best, and given its flexibility and updatable design, there's a strong possibility that it may remain the best for longer than one issue of this magazine.

The Rhodes Chroma is distributed in NSW by Greg Hutchings of Hutchings Keyboards, 9 Edgecliff Rd, Bondi Junction (02)387-5507. Inquiries from other states can be directed to Greg or to the indent agents Peter O'Loughlin and Co, 20 Ploughman St, North Bondi NSW 2026 (02)309-1741.

Chroma 21040006 was for sale on Australian eBay in February 2005 and sported a Hutchings Keyboards sticker:

Recommended Retail Price: [Australian] $7650