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Music UK: The Rhodes Chroma

By Vince Hill

This article is from an issue of Music UK acquired via an eBay auction, and is from 1982 (probably November); see the Bibliography for more information. I have not been able to find who owns current rights to the magazine, which appears to be long defunct. If you have any information, please let me know.

(RRP £3,800 inc. VAT)
Over the last few months I have looked at a variety of polyphonic synthesisers utilising within their design some type of digital generation, either in the form of a DCO or with a microprocessor on board. The Rhodes Chroma is computer based, having two microprocessors within its housing, any analog controls are encoded digitally and then processed by the central computer and sent to the synth channels. The Chroma may be used very simply or with great complexity depending on you not only as a musician but as a sound technician. It is well designed, as there are touch sensitive membrane switches flush to the panel, most of which have dual modes. The ergonomics of the instrument are not in question. The unit is manufactured with wood surrounds and metal control panel giving a very solid look and weight to it.

The keyboard is touch sensitive, one of the two microprocessor controls and understands the keyboard response. It is a weighty keyboard, and you do feel you are nearly playing on acoustic piano yet the velocity sensitive keys allow very delicate manipulations. For those people who remember ARP and might have purchased one of their voiced pianos, the touch response is very similar. The Chroma was a design from ARP and when they went broke in 1981 CBS/Rhodes purchased the project [see The Rise and Fall of ARP Instruments]. So, the keyboard computer controls the 64 note keyboard and can apply its control voltage to the amplitude and be programmed for pitch, waveform, cut off, filter, modulation rates and envelope control. The keyboard can be split at any desired point by means of--yup you guessed it--the Set Split command. We are going to look at the Chroma mainly from the preset performance angle BUT (and as you see it's a big but) it does extend to a complex programming and sound generation tool and beyond that the eventual interface with another computer. This would allow the computer to play the Chroma's keyboard and performance controls, it could act as a complete digital event recorder, remembering what is played by the musician--not just the notes, but all keyboard expression and controllers. The computer could be used to change sounds and to modify required parameters in existing programs plus recognise alterations made by the player on the panel controls giving a huge library of subprograms and with the use of the cassette interface it can load or store immense amounts of programmed data.

The central microprocessor in the Chroma is used to digitally generated all of the control signals. The computer generates 16 channels which are linked into 8 pairs, each channel has an oscillator, waveshaper, filter and amplifier; also generated are 32 envelopes (2 per channel) and 16 Low Frequency Sweep signals. The Sweep signal is akin to an LFO; as there is no need for separate oscillators to control modulations of the sound it is now a control function on the Chroma, with its rate and waveshape being variable.

You are able to have a sixteen-voice patch if required, however, most will be of the eight-voice type allowing for the way the computer pairs the channels. This is in normal mode, the whole keyboard playing the same program; you can change this to use two programs together, either in Unison or using the Set Split to obtain one program for the lower octaves and another for the top end. This is particularly effective as you can choose where the key split should occur. The process for this selection is made from a series of switches with LEDs above to confirm operation, aptly named the Two Program Linkage, consisting of No Link/Link Lower/Link Unison/ and Link Upper, above this are four switches for octave transposition, you are able to take the Main program up/down 1 octave and able to do the same for the Link program. The Main program is the sound currently controlled by the computer, ie all of its parameters may be altered, the Link program is controlled by one of the fifty stored programs. Its parameters cannot be altered at will until it is made the main or current program.

This ability allows for some devastatingly rich sounds and full effects, particularly in Unison--obviously when using Set Split you obtain two distinctly separate tones. When in the Unison mode, the number of voices or keys played is decreased depending on the oscillator allocation within the two programs, you must be aware of this when considering the Chroma as a live performance synthesiser. You are also able to set the Link program as part of the integral program so that it will automatically produce the two sounds when required.

Before going onto the actual program sounds let us take a look at the remaining controls on the left hand side of the Chroma. There is a fine tune slider variable to plus or minus one semitone, when needing a wider tuning range you can edit the Tune parameter which is the dual mode on program 26. Next are three sliders: Bass/Middle/Treble for the Mono Out Eq, an overall volume slider, a series of switches for Cassette Interface, Set Split, Store, Edit Mode A/V and Auto Tune. This latter switch does the same as switching the instrument on [sic], all LED's flash wildly at you as the computer searches through for faults and to tune each of the 16 oscillators and filters. When the LED's stop the tuning is complete, if there is any fault or a channel does not tune correctly, you will see in the Data Readout display an error message "Err" followed by the defective channel number. Next we come to the controls we will use in the 'live' sense. There is a long lever for Parameter control and two readout windows, one showing the Program number and if there has been any modification to it, this window is quite large and can be easily seen on a dimly lit stage; underneath is the Data Readout window showing two numbers, the parameter which can be changed directly by the slider to modify the sound and the numerical value of the slider, each facility has a different range of values. The Data Readout will show which Link a program has with another. Under this display is the Panel Mode bank, again four switches; Parameter Select, Copy from A, Copy from B, and Program Select. The 'Copy From' switches are used for editing/creating programs and there are a number of temporary panel modes which can be achieved by pressing two switches in a determined sequence. These are confirmed when in operation by a flashing LED. So pressing the program Select and looking to the bank of fifty switches on the right here we go.

This bank of controls are flush membrane but without LED's. They have dual purposes legibly numbered they contain the first of fifty programs (you get a cassette with a further 100 programmes when purchasing the Chroma). When selecting Parameter Select the switches revert to the parameter function which is written above the number, this function is then altered by the parametric lever.

The Brass programs ranged from full throaty ensembles to slurring solo trumpets, the chimes, gongs and bells were very clean and using the parameter slider to change pitch or modulation depth gave full tonal and timbral variants. The pitching of these matallic [sic] effects was easy and extremely precise. The Flute was wonderful with the push breath and subsequent vibrato being well timed. Some of the effects were arpeggiated, one program when playing a four note chord allowed the top percussive tone to arpeggiate fast and rolling whilst the underlying bass tone played in sync. but at a slower rate. The speed of the bass line was parametrically controlled, its top speed syncing directly. The Clarinet was superb, strong and hard, the degree of touch sensitivity was quite startling--it was surprising how hard you could hit the keys to obtain varying degrees of programmed touch sensitivity. The strings were of the slow quartet type, the cellos were excellent. Program 28 was linked with 27 producing full orchestral strings.

Program 1 was a heavy thick filtered percussive growl with a fast and high modulation effect with slow but slight portamento, the parameter level is set here to give more emphasis to either part of the total sound. Program 23 was a rich percussive organ tone, the parameter was 47 which translated its Mod 1 Depth, this adjusts the gain of the No 1 modulation input into the amplifier. The result of increasing this parameter transferred the tone to a bring and heavy percussive jazz organ, a really good sound. 32 was a slow attack, fat filter sounding exactly like the bass line from Midnight Express with a faint sweep phasing through the sound. Prog 40 was weird: the entire keyboard had been changed tonally so the bass was at the top and vice versa. For the first time my bass solos were great! prog 43 linked with 42 produced a dynamic sustained sawtooth tone with random sequencing effects rising and falling in the background. 44 was an immediate echo repeat, the spacing being altered by the parameter level. prog 47 was very interesting, a low percussive thump but with overtones and depending on what notes or chord variations you played you obtained a whole host of rhythmic tones.

I loved prog 48. The initial sound was of chimes and bells all in different tonings, but if you keep the notes pressed down a sequence of hundreds of clocks chiming emitted. 49 was the most perfect sea noise, gulls, surf, shingles, and the occasional ringing of a bell--presumably on a buoy. I could have been drifting in the middle of the Channel! I was able to edit the attack and release of the surf which worked a treat. The last program was the sound of gulls and birds and increasing the parameter (sweep rate) you had the frenzy of Hitchcock's Birds surrounding you!

So there are some of the sound effects available, the Chroma allows total control depending on your imagination. The sound is strong, clean and effective. There are three seperate [sic] manuals with the instrument for performance, programming and computer interfacing, the unit is supplied with a flight case and all foot pedals that hook up to the rear to give quick live performance control. Within the Chroma manuals you begin to realise the hidden capabilities of the instrument, as it is computer based there are facilities to diagnose faults, obtain stereo set-ups, programming aids, subroutines, interfacing commands and many more.

The Chroma is not to be taken for granted, nor at face value. It does its job more than admirably and is realistically priced for a monster of a machine!