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Keyboard Report: The Rhodes Chroma

By Dominic Milano

The following article is being reprinted with permission from Keyboard Magazine, August, 1982.

There was a time when the word synthesizer brought on visions of surrogate switchboards; miles of patch cords hanging from their fronts interconnecting hundreds of modules. You needed hours to get through the tangled mess to see just which modules were functioning in very complex patches. These days, things have changed in ways that reflect changes in technology. The switchboard image is more or less gone. Nowadays you're more likely to see very austere front panels with just enough knobs and dials to get the job done in a live performance situation (of course, it may still be a little tricky figuring out what's being routed to what). Computers are taking a more active role in the instruments too, helping to make things faster in live performance by remembering patches. Most recently (even not considering the high-powered all-digital machines) computer technology has been called on to assist analog tone-generating circuitry, which can increase the flexibility and operating speed of the synthesizer while bringing the cost down.

The Rhodes Chroma is one of these analog/digital hybrid instruments, incorporating two microprocessors in its design. One is to keep track of the keyboard functions, the other is to store program information (patches) and to generate things like LFO functions and envelope functions -- things that a computer does very well. The computer in the Chroma also allows you to play some very fancy tricks. For example, instead of being stuck with one configuration of two oscillators, a filter, two ADSRs, and a VCA on each voice, you can alter the configuration in a number of different ways. You can put two filters on each voice, put them in parallel or in series, put the amplifiers before or after the filters, and so on.

Of course there is a tradeoff. In order to operate this software, you have to learn to use a set of controls that operate rather differently than the knobs on the familiar synthesizer. The Chroma's front panel has 50 membrane switches on it which are made to serve dual function. In one mode of operation, they call up presets. In the other mode, they call up various parameters of the patch, one at a time, to be altered by adjusting a single slider control, as on the Synclavier. It's an approach that takes some getting used to, but it's not hard to learn and it does save the manufacturer a lot of money in parts, so the savings can be passed on to the musician.

The Chroma is the first synthesizer project that Rhodes (as in the Rhodes piano) has undertaken. However, the Chroma was in fact designed by ARP Instruments before ARP went out of business in 1981. CBS, the parent company of Rhodes, bought the Chroma and hired the staff of engineers from ARP that worked on the project. So it's no surprise that it has a sound very reminiscent of the ARP sound and a velocity-sensitive keyboard like the one on the ARP 4- and 16-voice pianos.

The Keyboard

This has kind of a strange range: 64 notes, E to G. It's velocity-sensitive and that sensitivity's control voltage can be applied by the computer to a number of different places, such as the pitch, the filter cutoff, the rate of the LFO, the waveshape, amplitude, and attack time, all of which are very useful parameters to be able to control with velocity sensitivity. Variable attack time and waveshape were particularly interesting. There is a programmable split point, available anywhere on the keyboard, and the keyboard algorithm is programmable too--that is, it has 16 different modes that it operates in, ranging from monophonic single-trigger to polyphonic pitch ordered (voices are assigned to notes in the order they're played at) to monophonic arpeggiation modes (four of those in addition to a sequencing mode). The action isn't as firm as an acoustic piano's, and some people might find that objectionable, but if you're playing a synthesizer with a velocity-sensitive keyboard you don't necessarily want a piano-like action. The Chroma's action was at a comfortable median between a stiff piano action and a wet noodle synthesizer action.

The Controllers

To the left of the keyboard are two levers whose functions are programmable. [You] can have one bending pitch and the other sweeping the filter, or you can have one changing the rate of an LFO while the other changes the rate of another LFO. You can even have them change voltage in different directions through calling up one as a negative voltage and the other as a positive voltage. There are two pedal inputs -- one pedal is supplied with the instrument -- for 5-volt pedals whose functions are similarly programmable. However, the pedal that was supplied with the instrument we reviewed was a bit squeaky mechanically and had an uneven response (nothing much happened at the bottom of its travel, but quite a lot happened very suddenly when you got to the top). A pair of piano-type brass footswitches are also supplied with the instrument. You can program them to operate in eight different modes, some of which are esoteric but very intriguing. For example, you can set it up so that you get no sound until a pedal is held down. That produces some interesting effects when you've got two sounds linked together on each key with one of the sounds being turned on and off by the pedal.

The Left Front Panel Controls

The front panel of the Chroma is divided by a thin strip down the middle. To the right of it are the program/parameter switches and to the left are various controls, including a master tuning slider, bass, treble, and mid EQ tone controls, a master volume control, switches for using the cassette interface function, four octave transposition switches, four two-program linkage switches, an auto tune switch, a switch for programming the keyboard split, and a program store switch. The transpose switches let you transpose the main and linked programs up or down one octave.

In order to understand the concept of main and linked programs, you need to know how the Chroma's oscillators, etc., are assigned to voices. The Chroma has 16 channels, each with an oscillator, filter, and amplifier. Normally, the channels are divided into eight pairs whose configurations can be programmed, which means that normally the instrument will have eight-voice polyphony (although you can have sixteen-voice polyphony on a patch if you're satisfied with a one-oscillator tone color). When you call up a program all eight channels can produce the same sound, or you can link two different sounds together so they can be played simultaneously, either in unison (two sounds on the same key) or with one on each end of a split keyboard. Obviously, when you link two sounds in unison, the Chroma becomes a four-voice instrument. You can get some very thick and beautiful tone colors by linking sounds together, as well as some very interesting effects (two sequencers going at the same time at different speeds with different tone colors).

To the right of the link switches is the parameter control, which functions as both a switch and a slider pot, depending on 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 it's a slider pot it's silent. To the right of the parameter control is a small LED readout called the data display that can show various things depending on what controls are activated. Its basic function is to show which parameter the slider is currently affecting, and the value that the parameter is currently set at.

Underneath the parameter control are two switches for controlling the edit mode. Since each of the eight oscillator cards has two channels, an A and a B channel, the edit mode switches are necessary to determine which channel the parameter control is controlling. You can activate Edit A, Edit B, or both simultaneously. In this case, however, when you call up a specific parameter, the data display will show only the value of the A channel setting. If you then move the parameter control, both channels will jump to the same value. What's useful is that you can program into any patch the type of edit mode you want and the parameter that you most often want to alter with the parameter control.

Next to the parameter control are the program number display (a larger LED display), the data readout, and four switches for controlling the mode of the program/parameter switches on the right side of the panel. The number display seemed a bit dim to us. You might want to build a little hood for it and the data readout to shelter out room lights. When you change any parameter as compared to the value stored in memory, a little period will appear in the lower right of the program number display to tell you the program has been modified. The data readout, instead of telling you the parameter number that's being modified and the parameter's current value, will also show the number of the second program when two are linked together; in this mode, the parameter control functions as a balance control for determining the relative volume of the two programs, and the data readout gives a balance figure in 2dB increments. The system of using a single slider and a readout to show you what parameter you're changing is one that takes some getting used to, but after you've been working with it for a few hours it will probably feel very natural.

The four panel mode switches determine if you're selecting a new program, a program parameter, or copying a program parameter value from the A to B or vice-versa.

The Right Front Panel Controls

These are a set of 50 switches, which as we've said can function as program select switches or parameter select switches. Selecting a program is simple. You just press the program select switch, followed by the number of the program you want to call up. If you're calling up a parameter things get slightly more confusing. You still just have to hit the parameter select switch, followed by the appropriate number switch for the parameter you want to edit. That part is easy. What's not so straightforward is remembering what the little numbers in the data readout mean in a particular case. To help you out, Rhodes has included with the instrument a chart that shows what parameters are controlled by what switches, and what the numerical values are. Each of the 50 switches is labelled with a word such as "rate" or "mod depth" in addition to its number, but remembering which modulation source or keyboard algorithm corresponds to which data readout number isn't that simple, since there are 15 or more of them.

Now, the big question is, what parameters do you get control over? There are 50 of them, as follows: (1) sets configuration of oscillators, filters, amplifiers -- 16 possible; (2) sets 8 possible footswitch modes; (3) 16 possible keyboard algorithms; (4) detunes oscillators; (5) selects between the four outputs on the back panel; (6) sets the glide rate; (7) chooses between portamento and glissando; (8) four different types of synchronization for the LFOs; (9) adjusts the rate of LFO sweep; (10) 16 possible modulation sources for the LFO; (11) selects 16 different LFO waveshapes; (12) modulates the depth of modulation from the LFO; (13) sets the envelope peak as a function of key velocity; (14) sets the attack speed of the first envelope generator; (15) 8 sources of modulation for the attack time; (16) varies the decay rate; (17) 8 sources of modulation for the decay; (18) adjusts the release time; (19) sets a delay time between the moment a key is struck and when the second envelope starts; (20) controls the relationship between the keystrike velocity and the second envelope amplitude; (21) varies the attack time of the second envelope; (22) 8 sources of modulation for the attack time; (23) sets the decay time; (24) selects from among 8 decay modulation sources; (25) adjusts the release time; (26) controls the tuning of the oscillators; (27) selects from among 16 different modulation sources for the pitch; (28) controls the frequency modulation depth; (29) a second modulation source selector for the pitch; (30) controls the depth of the second source of frequency modulation; (31) a third modulation source selector; (32) a third frequency modulation depth control; (33) selects the waveshape; (34) adjusts the width of the waveshape; (35) 16 modulation sources for the waveshape; (36) a waveshape modulation depth control; (37) determines whether the filter acts as a highpass or a lowpass filter; (38) a filter resonance amount control; (39) a filter cutoff frequency control; (40) 16 modulation sources for the filter cutoff frequency; (41) a filter cutoff frequency modulation depth control; (42) a second filter modulation source selector; (43) a second filter modulation depth control; (44) a third filter modulation source selector; (45) a third filter modulation depth control; (46) selects one of 4 different envelopes as modulation sources for the VCA; (47) varies the depth of modulation from 46; (48) selects a second envelope as a modulation source for the VCA; (49) varies the depth of the second envelope modulation the VCA; (50) selects one of 8 different sources of modulation to the VCA.

All that isn't as complex as it sounds, since in most cases the 16 modulation sources are the same, the depth controls are self-explanatory, and the effects of most of the other controls are plainly audible as you make the change. You can pretty much get by without ever reading the extensive owner's manuals, but if you really want to understand what's going on in this instrument, reading the manuals is highly recommended. However, a little more confusion will set in when you find out that there is a set of subroutines that makes the 50 right front panel switches have a third set of functions, such as setting up temporary link parameters, controlling Chroma-to-Chroma interfaces, muting channels, and resetting the main computer. There's also a lot to keep track of mentally with each patch you set up, since you'll have no immediate visual feedback on parameters other than the one you've currently got called up.

The Back Panel

There's a multipin connector for interfacing the Chroma to a computer (an interface for the Apple [II] is planned, and we're told it should be available by the time you read this -- cost is projected at about $100). Outputs are plentiful. There are two XLR outputs, 1/4" high- and low-level mono outputs, and four 1/4" audio input/outputs. These can be used for routing the outputs of four separate channels in quad or for doing effects send and returns -- a very useful feature. There are also inputs for the dual footswitch controller, a sequencer input for controlling the clock of the sequencer externally [this is incorrect--it's a program sequence footswitch for moving from one program to another], and two voltage pedal inputs. The cassette interface output is a DIN plug -- it's not very common to see DIN plugs used anymore, but one is supplied with the instrument and most electronics supply houses still carry them in case you need to replace yours. Still we would have rather seen a plug that a musician is likely to have some spares around of -- a 1/4" phone plug most preferably, or an RCA plug -- but you can't have everything. Then there is a lock/unlock switch for protecting the memory when you don't want to accidentally blank a patch, an on/off switch, and a removable power cord.


You've probably gotten the idea that the Chroma offers a lot of function buried under a deceptively simple front panel. That front panel is probably both the instrument's strongest and its weakest point. Someone who doesn't want to get involved in programming and who's intimidated by a lot of knobs and dials can just punch up presets very easily without being bothered by a lot of confusion. But the person who's used to analog gear with knobs and dials may find the Chroma's flat panel foreign-looking. Some of the presets that the instrument is shipped with are quite nice-sounding, while you may want to re-program others to give them a more distinctive character. It's safe to say that the Chroma offers more potential for distinctive tone colors than just about any analog instrument we've seen yet, but it's also safe to say that you'll have to do a certain amount of head-scratching figuring out how to get at that potential, since a lot of the possibilities aren't readily apparent.

In terms of live performance, we suspect that it would be tricky to adjust your tone color with the single parameter control quickly on stage, particularly because of the small size of the data readout, but once you get the programs set up the way you want them, this shouldn't be a problem. One feature that we would have liked to see that wasn't included was a programmable loudness control for matching the levels of the various programs. The volume control on the front panel created drastic level changes with only a small amount of movement, and this will probably take a little getting used to as well.

Cosmetically, the Chroma has wood sides and metal panels on the top and bottom. It would be a handsome instrument if it weren't for the green and blue front panel controls. They're a bit on the ugly side. Also, while the program select switches have large white easy-to-read numbers, the parameter labels over the numbers are in black letters on dark blue or green -- not too easy to read. Although the switches don't move when you press them, something under the front panel makes a satisfying 'thunk' so you can tell you've done something.

The instrument we had to review was one of the first 50 built, and with this in mind we've got to tell you that it glitched every now and then. The computer locked up a couple of times for no apparent reason, and turning the instrument off and back on helped sometimes but not always. Sometimes leaving it off for 15 minutes was the only answer. We were told that the problem was in a set of faulty E-PROMS that won't be in the units that go on sale, so consumers shouldn't have this problem. We'd suggest that you play the instrument for a while in the store in order to check it out before you buy it.

Overall, the Chroma gives you a great deal of synthesizer power for your money. The instrument comes with an Anvil flight case, a voltage pedal controller, two piano-type footswitches, and a cassette with 150 programs on it (50 can be stored in the machine at one time). A pressure sensor option for the keyboard is going to be available sometime later this year at a price of about $300. Suggested retail price for the current system is $4,995.00.