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Primed For Launch

Chroma Polaris

The new Chroma Polaris Polysynth. Will it self-destruct?


Mike Beecher takes off to review the Chroma Polaris, a £1,700 polysynth designed to conquer.


The original Chroma instrument technology has been handed down to the Polaris — outwardly evident from the multifunction 'touch pad' and slider control panel, although the more complex Chroma algorithms are restricted to setting up what amounts to the most comprehensive in/out links on an instrument in this price range (£1700).

Not only does it provide a host of MIDI functions, but it also links to its mother keyboard, the Rhodes Chroma, and has sync matching that means you won't need a Dr Click to make its sequencer fully compatible in the studio.

Shades of Blue



The Polaris weighs and sizes up like a Yamaha DX-7 and is enclosed in a rigid steel chassis with plastic trim and shaped black wood end pieces that finish off its low profile.

The main control area above the 61-note C to C keyboard has a Chroma-style touch panel with its microswitches (underneath) located by light or mid-blue coloured pads. There are 20 short run sliders for adjusting the synthesiser's sounds when editing or creating a 'program' voice played from the keyboard or built-in sequencer. Slide setting can be rather hit and miss if you're used to patch-charting your sounds because no number scales are shown, just black stripes on light or mid-blue backgrounds for each that show where 'off' setting should be. From one to four functions on each pad can be switched using 'lower function' or 'upper function' pads beforehand for the appropriate control. Besides having a built-in red LED on each pad for on/off indication, the Polaris features an LED signalling system that keeps you informed of where to go next, during recording for example, and stepping back a stage to show the last program sound chosen — this is a very useful way of helping you along when there's no other means of display.

At the rear a large heatsink is seated flush with the panel next to a 3-pin Europlug power socket. Other connections are MIDI in, out/thru, a Chroma interface socket, stereophones and 100K assignable swell pedal plus low and high level line outputs, footswitch sockets for sustain/glide and metronome/tempo control, sync in/out and cassette recorder 5-pin DIN sockets.

Polaris Soundmaking



The Polaris has a different kind of operating system from most synths, using memory sharing for putting in program sounds and realtime music sequences. So you can either fill up the 132 possible program locations with different sounds or cut down on the number of programs in order to get some sequences as well. One thing that CBS must show in the user manual is some guide to the different combinations of programs/sequences that could be obtained with the instrument as it stands — there is in fact extra space inside the Polaris for inserting more memory, adding four or five times the capacity.

The soundmaking uses two oscillators to each voice for its 6-note velocity sensitive playing, with analog-style controls for synthesising the program voices. There are 11 vertical sections across the control panel for sequencer, keyboard program linking, master volume and tuning, synth parameter control (including an assignable section for pedal/footswitch control, oscillator modulation and detune), plus a large group of bank/program select touch pads that will call up program sounds by a letter (A-K) and number (1-12) combination as well as allow programs and sequences to be saved, loaded and edited. Finally, there are important 'housekeeping' functions for setting in and out routing, MIDI diagnostic checks and various operating adjustments.

If you've spent some time with analog keyboards, you'll find the Polaris has straightforward synth sections covering oscillators one and two, sweep (LFO), filter, envelopes for filter and volume, and assignable controls. The instrument comes with various programs and sequence examples stored in its memory and you can either edit these one at a time or take an empty (or deleted) location which then sensibly gives you a basic organ-type sound to start with.

The range of control with the various parameters in the synth sections is very good and essential features, like dual oscillators per note, are all here — even though there are only two types of wave source: sawtooth and pulse, because these can both be varied directly by the Pulsewidth (PW) slider or by the Pulsewidth Modulation (PWM) slider (normally it's only pulse). PWM can be from either the so-called sweep oscillator or the filter envelope stage. By varying the sawtooth wave, you get a change from the fundamental to the first harmonic that has a nice range of timbral textures. Pulse goes from off at end settings to narrow pulse and square wave and back.

Envelope and volume envelope controls.


The pitch setting of each oscillator is done by a transpose switch that takes overall pitch from a selected keynote — very large intervals can be selected in this way and quickly updated.

Ring modulation can be added from Osc 1 section to give metallic clangs and bizarre frequency swoops (with pitch modulation), and 'Sync' pulls both oscillators' pitch together, making distinct timbral changes as well.

Modulation of the pitch and filter is set by the sweep section, providing simply sine or square wave control at a rate set by the slider, from one cycle every 13 seconds to over 50 Hertz.

The low pass filter section has the usual cut-off, resonance, sweep depth, envelope depth and keyboard tracking controls on sliders. The resonance control will put the filter into oscillation at max settings or discriminate the harmonics just prior to this. 'Keyboard Track' can progressively brighten up sounds on lower or upper keyboard ends.

White noise can be brought in here for getting plenty of effects: sea, wind, and thunder to spaceship take-offs and the like. But true random variations cannot be made and this is a notable omission, particularly with effects. And the only way you can turn off an oscillator (to use just the noise source) is to put the pulse wave at extreme slider positions.

Two envelope shapes act on filter and volume respectively. The filter envelope has normal attack, decay, sustain and release sliders, plus a sustain decay slider for creating another cut-off level during keying. No high pass or band pass filtering is available and the volume envelope is a simple ADR type, with 'hold' obtained by putting release at maximum. Both envelopes can be 'fixed' or 'touch' controlled from the keyboard for timbral and dynamic variation from its velocity-sensitive keyboard, and the 'adjustments' section will allow you to set the response to suit your playing.

Taking the Chroma's one control for setting most parameters' idea — a popular hardware economy on several instruments like the Korg Poly-800, Poly-61, Yamaha DX etc — the Polaris has one control switch in its assignable control section for setting the glide rate (this is a top-note-only effect turned on by footswitch (1), footpedal control of sweep rate, vibrato depth, oscillator pitch, filter cutoff frequency, and output volume, program volume, modulation lever and pitch bend lever range (these controllers are located to the left of the keyboard).

Vibrato depth can also be set for osc 1 and 2 independently, with a shared variable delay of up to two seconds (maximum effect at six seconds) making a more natural acoustic instrument effect or dramatic swoops at full setting. The vibrato rate is set by the sweep slider. Alternatively, or in combination, the pitch can be modulated from the filter envelope for interval jumps and slides on each new key played. Detune completes the assignable controls and is the only means of getting ensemble and 'honk-tonk' sounds, since no chorus is provided. Still, you'll hear on the tape that strings are quite acceptable by this method when oscillator vibrato is added as well.

The 'Master' section has one slider and a 4-function pad, normally for setting main output volume, but also able to tune one or all six synth voices automatically (the LED flashes for each osc. tuned and a soft tinkling noise heard!), as well as setting overall tuning to match other instruments.

Left hand keyboard functions and performance controls.


This is one of the few instruments that can link two programs together and despite the reduction of poly notes to three, you'll probably find that linking two together in unison can give you the most impressive sounds. Two programs can also be linked to upper and lower sections of the keyboard, with the actual split defined from a note played and an optional one note higher setting matching low and high ranges suitably.

The combination of two programs in this way can be saved as a 'linked' program in a free location, storing all the link details for recall in performance. Editing of the link functions or one of its two program sounds used can also be done easily.

Multi sequencer



Several polysynths have built-in sequencers, some of which are more like arpeggiators because of their very limited storage. The Polaris stores around 1,500 events for one or more sequences, although I found in practice that I could store some seven sequences as 10-second riffs, up to one 3-minute backing sequence and still leave room for 72 programs in banks A to F (played on the demo). Up to 12 sequences can be recorded in, all from the keyboard, through the MIDI or from another, Chroma/Polaris instrument.

The sequencer controls are kept to a minimum with Stop, Record and Play pads showing current metronome/tempo from their LEDs. The tempo for record and playback can be set from external sync or MIDI timing as well as internally. Using the latter as the 'master clock', it is possible to sync up drum machines, sequencers and instruments to play together, and the Polaris can initiate a new tempo very simply from a couple of taps on footswitch two in time with your beat.

There appears to be no editing except to re-do the whole sequence again (no manual supplied!). Nevertheless, the program sound used to record the sequence will be saved, along with note data, key touch and performance control such as pitchbend and vibrato.

Housekeeping



Once you've created sounds or sequences you can use the Bank Select/Program Select section at the far right of the control panel to manipulate these in various ways. Other 'housekeeping' tasks are also carried out here for setting in/outs, parameters and performance adjustments or service checks.

Programs are handled in much the same way, and selection of the current program is the normal use in performance of this section on power-up and after saving or loading. Programs can be stored, erased, swapped, saved or loaded singly or all at once on cassette.

Master Keyboard



As you build up your collection of MIDI keyboards, you'll need a 'master' keyboard to do your playing and controlling with other instruments (unless you use a micro-linked system that can handle all your requirements) and the Polaris could well fit the bill as long as you did not want pressure (aftertouch) response (as on the DX-7) or weighted keys (as on Roland MKB-1000).

There are still more functions hidden away in the Bank/Program select section under the labels Cassette, adjustments, interface, Metronome, Sync in, Sync out and Diagnostics.

Bank select controls revealing 'hidden' functions.


The Cassette options give save and load monitoring, Chroma panel control, MIDI parameter control and mode selection, Polaris to Polaris program exchange, and connection to MIDI.

Diagnostics show battery back-up condition, current software number in use, LED check and one location to be avoided (D, 12) that erases all programs and sequences!

Adjustments to the click volume of the metronome while using the sequencer can be made, and the touch pads can have an audible click or buzz too, and there is slider adjustment of lever range, pedal volume, volume envelope and key velocity sensitivity.

The Interface functions will switch the Polaris' three main controllers: instrument, link and sequencer, to MIDI in/out and to the Chroma interface.

Sync is a real winner for the sequencer as it will alter in and out clocks separately to match 12, 24, 48, 96 or 192 clocks per quarter note, with negative or positive polarity and dual switching levels for TTL or CMOS. Sync to tape is also possible direct from the machine, with 1200, 600, 400, 300 and 200Hz setting.

The sequencer's metronome can be slaved to the internal clock, sync in/out and/or MIDI in 12 different combinations that reinforces the Polaris's worth as a master keyboard. Each of the six voices on the instruments can be switched in or out, should a fault occur or some form of reset condition appear from MIDI.

I mentioned earlier that there are three control areas within the Polaris: main keyboard, link and sequencer, and these independently produce information first, from the split or full keyboard (including performance, program and parameter changes). Link will send out all the changes made in the keyboard section and even send info during parameter edit.

The sequencer can receive and send to MIDI, handling all program voice, note, velocity and performance changes as well as timing codes for MIDI-equipped drums and sequencers. In fact, the Polaris will also receive Yamaha's pressure control and output it again on sequence playback even though the current Polaris synth doesn't recognise this. Computer links to the Polaris will be the inevitable step in getting the most communication out of your set-up and the major MIDI software companies like EMR, Jellinghaus and Rittor/Passport will no doubt provide packages in this direction.

The big feature of the MIDI control is that all parameters are communicated and that, combined with footswitch control of sequencer tempo (and anything else that's connected!) make it a powerful system.

This makes it one of the most versatile programmables to date under two grand and it could well be the ideal complement to digital and FM machines, not only in sound, but for taking in sequences as well.



Previous Article in this issue

Beauty And The Beat

Next article in this issue

The Lizard King


Electronic Soundmaker & Computer Music - Copyright: Cover Publications Ltd, Northern & Shell Ltd.

 

Electronic Soundmaker - Nov 1984

Donated & scanned by: Mike Gorman

Gear in this article:

Synthesizer > Rhodes > Chroma Polaris


Gear Tags:

Analog Synth
Polysynth

Review by Mike Beecher

Previous article in this issue:

> Beauty And The Beat

Next article in this issue:

> The Lizard King


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