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International Musician: Synth Check/Rhodes Chroma

by Paul Fishman

The following review is being reprinted with permission from International Musician, January 1983. See the Bibliography for more information.

(Marks out of 20)
Performance 14
Tonal Quality 16
Construction 10
Tonal Variation 19
Value for money 14
Total % 83

Question: when is a review not a review?

Answer: When it is impossible to spend enough time with the equipment to fully absorb all its functions and truly understand how it operates. I'm afraid that recently this has become an increasing headache for me. As each week the instruments become further technically advanced, it is harder to just browse over it and actually take in enough information to give one an instant sense of how it works. This matter is further hampered by manufacturers being unable to hand over their latest gizmo for the purposes of testing, due to whatever reasons such as all stock being in the shops. This is fair enough, but what we are talking about here is equipment that costs thousands of pounds and uses advanced computer logic to control its functions. i don't have any sympathy with anybody who goes out and spends a lot of money on something that they don't really understand. You are either mad, stinking rich, or just plain stupid. Some might be even lucky enough to combine all three.

So not being put off by this matter, I decided to take the viewpoint of what it would be like if I just strolled into a music shop and said, "Excuse me, but I would like to see the Chroma." And this is exactly what I said when I recently payed a visit to Argents Keyboard shop in Denmark Street, London. Thus creating an environment of street credibility to this article (Oh wow). Much thanks to Mickey of Argents who gave me the 'instant Chroma mix it with water' demo.

Who is this guy anyway?

This is the bit where I go into the family background and tell you how many 'O' levels they've got and general hereditary [sic]. You know, whether its mother was a hamster and did its father eat elderberries(?).

Well the Chroma was originally designed by that wonderful company of days gone by, namely ARP. Them of the 2600, Odyssey, Pro Soloist Rhodes [?], as in pianos [?]. (The plot thickens.) The Chroma is the only keyboard out of the ARP range that has been developed, as to my knowledge all the others have ceased to be manufactured. I am informed that it has inherited some of the original qualities of their old range of keyboards. Exactly what, I'm not really sure. The development of the Chroma has been in the air for quite a long time now, and rumours of its arrival have been around for about two years. I assume this time was spent developing and de-bugging the instrument from its initial teething problems. But more about that later.

The Rhodes Chroma is of the analogue/digital hybrid instruments (like the OBXA, Prophet and JP8). Basically the pitch is generated from an analogue source, ie -- an oscillator, and is then treated by other analogue processors, eg -- envelope shapers, filters etc. The digital side of it is used to control various parameters of the generated sound and to store programs (or patches). It uses two independent microprocessors to run these functions. The Chroma has gone one step further than most of its present counterparts, and that is to use the computer like an internal patch bay. In the good old days 9before they dropped the bomb), synthesizers were huge modular efforts that you patched all the various bits together with vast quantities of leads, giving the appearance of one of those old fashioned telephone exchanges, or as it was known, 'spaghetti junction.' The advantages of this sort of system was that you could patch anything into anything else, in any configuration you liked. This was very interesting and could be highly educational and creative, as it allowed the user to explore synthesis far more than the form in which keyboards are manufactured today. Now everything is hardwired and you have no choice apart from the way the designer decided how you could use it. This is obviously limiting. The disadvantages of the modular system was that basically it was a pain in the posterior. By using the Chroma's facility to assign what and where, you aren't stuck with the usual configuration of two oscillators, a filter, an ADSR and a VCA for each voice. You can alter the patching configuration in various ways. For example, you can put two filters per voice, put them in parallel or in series, put the amplifiers before or after the filters, etc...


There are eight dual channel synthesizer circuit boards, which means that it has a 16 voice capability but is mainly designed to be used so that all its voices are doubled up, and therefore allow far greater possibilities of synthesis by the combination of different sounds, or simply to enhance the basic sound by doubling the voices, creating that ugly expression 'a fat sound'.

Its 16 synthesizer channels (or more commonly understood by plebs like you and me as 'voices'), each consist of an oscillator, filter, waveshaper and amplifier. As already mentioned, the 16 channels are split into eight pairs, these are labelled either 'A' or 'B' and can be processed independently of each other. The computer generates 32 envelopes (two per channel) and 16 low frequency sweep signals. Signals from the levers, pedals, control panel or the keyboard are all encoded digitally, processed by the central computer, and then sent to the synthesizer channels. Everything including keyboard split, transposition etc can be stored digitally.

The two envelope shapers are both capable of generating either AR and ADR envelopes. By using two modulation inputs, say to the filter, the mix of these two will create the traditional ADSR shape. But what is particular in this case, is that they can be run independently. One could be set up to create a fast percussive attack while the other could be set for a slow percussive envelope, combined with two different delay times, you can use this to create realistic piano sounds. Alternatively, combining a short envelope with a delayed slow attack gives you (and I quote from the manual) "a sforzando envelope." (I'll translate, this is a new form of language called 'Techno-Italia'," this particular expression means a strongly accented or forced enveloped.) Both envelope shapers can be modulated by one of seven control signals.

The waveshaper can be selected to to either a pulse or a shape called 'Saws' which is a combination of a pulse and a sawtooth. The pulse width and the 'saws' can be adjusted from 0% to almost 100% and can be modulated.

The Filters work as either high pass or low pass and can be made to oscillate by the use of the resonance control. There are three modulation inputs.

The Sweep generator (no relation to Sooty -- Ha-appalling joke!) generates low frequency control signals (LFOs). Its rate can be modulated by one of 15 other control signals. It has 16 waveshapes available, including sine, triangle, saw, square and random. Its amplitude is modulated by one of 15 other control signals, including its own internal delay envelope generator. It can also be synchronised to key depression.

There are six different performance control signals. These are derived from the two floor pedals, the key strike velocity is available as a control signal, and key pressure is available as a hardware option. The level and pedal signals differ from all other control signals in that they are common to all channels.

The assignment of modulation inputs is highly extensive, if not to the point of being a little over the top. The oscillators have three modulation inputs and the filter three more, and the waveshaper has one. These seven inputs can be set to control which of the many modulations sources is to be used, and the depth of modulation. The 16 selections of modulation sources are the same for all of these inputs. They are:

  1. Kybd Glide A
  2. Sweep A
  3. Env 1A
  4. Env2A
  5. Kybd Glide B
  6. Sweep B
  7. Env 1B
  8. Env 2B
  9. Lever 1
  10. Lever 2
  11. Pedal 1
  12. Pedal 2
  13. Velocity
  14. Thresh Vel.
  15. Pressure
  16. Thresh Pressure

The keyboard has a range of 64 notes from E to G (don't ask me why). It is velocity-sensitive and its sensitivity can be applied to control things such as the pitch, the filter cutoff, the LFO rate, the waveshaper, amplitude, and attack time. The keyboard is designed with a weighted action and has caused much interest from musicians who have been waiting all their lives for 'piano type keyboards' to be available for synthesizer users. I personally couldn't give a monkey's bum, as I believe that you adapt your keyboard technique to suit the instrument. Although I did once upon a time study piano technique, I have spent most of my playing years working with bits of plastic and contact strips. When the piano came along, people didn't say 'why doesn't it feel like a harpsichord or a clavichord' the answer would have been, 'cos it's a bleedin' piano, mate!' So my feelings are to the current situation 'cos it's a bleedin' synthesizer, mate.' But each to his own, horses for courses, fish for water, one man's meat is another man's poison, one man's meat is a vegetarians' lentils, some days the bear eats you, other days the bear eats you, etc...I'm sorry about that, but I got quite carried away. I don't know what came over me. It must have been all that Blu-Tac that I've been sniffing.

There are 16 different keyboard modes, ranging from monophonic single trigger to polyphonic pitch ordered. That means that voices are assigned to notes in the order they are played. There are four monophonic arpeggiation modes in addition to a sequencing mode.

The Front Panel

Yes, it's got one! And odd it is too. It is divided down the middle by a thin strip. On the right hand side are the 50 program switches which also double as the parameter switches, on the left are various controls; master tun, Eq, master volume, cassette interface controls, octave transposition (up or down one octave), program linkage, you get the general drift. Next to these link switches is the most important control on the whole keyboard, and that is the 'parameter control', not the 'parameter control', yes the 'paramater control'. Well we had to get to it sometime. Without the comprehension of this control you are absolutely 'roast ducked'. It acts as both a switch and a slider pot, depending upon the parameter it's called upon to vary. When it's functioning as a switch you hear clicks for each switch position it passes through. When used as a slider pot it is silent. These clicks are somewhat disturbing to say the least. They are created by something inside the keyboard that causes a mechanical thump on the front panel. (A Woodpecker?) You not only hear them but you also feel them. A great asset if you are a blind keyboard player, but absolutely useless if you have no hands! (Or alternatively -- a major contribution to road safety.) These clicks also register in one of the two LED displays, as numbers relating to the amount of increments for the particular parameter you are setting. Though not all the settings have the same amount of increments, some don't seem to have enough degree of control. Which can be a problem. This concept of the 'master control' has previously been introduced by the 'Moog Source' which uses a similar principle, except that it uses a device called an 'optical wheel', which functions better than the Chroma's slider and has the advantage of not having parts that could wear out. This principle has also been applied with better results to the control of the Synclavier. The other LED readout you get, is that of the program number you are currently working with. The size of the parameter LED was ridiculously small. I'm sure on stage this could be a nightmare. Bring a magnifying glass, you'll need it.

As for the 50 parameter/program select switches, well for all of you who haven't copped a look at one of the adverts for this instrument, they are of the touch sensor/contact type and therefore have no real moving parts. I found you had to be quite positive with them otherwise not a lot happened. They also take on a third function; when setting up temporary link parameters, controlling Chroma-to-Chroma interfaces, muting channels and resetting the main computer.

Computer Interface

One of the selling points of this instrument has been that you can interface it with an Apple [II] computer or a Tandy TRS-80, just in case you had one lying around the house. Personally, the possibilities of this sort of connection I find very interesting (in fact it gives me the 'Trevor' -- in joke for producers). I can definitely foresee more companies following along these lines. I believe that when connected you can use the computer to program all parameter functions and particularly use it for complicated sequencing. Although as yet I haven't met anyone who has been able to do this, or in fact anybody who seems to know much about it at all.


The Chroma is a very interesting chap, as it doesn't quite fit into the Prophet, OBXA, JP8 league, nor does it fit into the Fairlight, Synclavier, PPGs ot. It seems to be somewhere between both categories, which may or may not be a good thing, only time/sales will tell? Despite the fact that it offers far more versatility than most synthes it is a pain to edit. You have to use the manual to remember all the information, unless you've got a photostatic memory, which I definitely haven't. It's all very well designing a versatile keyboard, but please spare a few thoughts for the musician who's got to use it. If you were using programs which you had to edit whilst playing live this could well be a real torture. Why couldn't it have been designed with far more access to operating information on the keyboard itself? The 50 programs it can store is all very well, but it does seem to be a little limiting considering that these days it is quite a low amount for on board memory, despite the fact that its tape dump system can reload in less than a minute. Which isn't that fast considering we live in the age of the floppy disc.

As for its looks, well I wouldn't say it's particularly attractive but I'm sure many current Chroma users would say the same about me.

I must also mention for any prospective buyers, do check the instrument out well and truly, make sure it is all functioning properly. I've heard different reports from lots of sources that early models have had a few technical problems. Initially people were told that these were teething matters and software faults, but still reports keep on coming in.

Finally the sound of the instrument. Well I'm sure if you sit down and do some really serious programming you can make some wonderful sounds. It is a versatile instrument, but of the factory sounds I heard, most were rather average and lacking in any real character or identifiable colouration. I would have also liked to have seen far more waveforms available from the main oscillators, as the waveshapes are the crucial building blocks of every sound.

Priced at £3800 appro, the Chroma ain't cheap. It's definitely got some good points, but was it designed by a musician? I doubt it!