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The Modular Approach

Expander modules may be the modular synths of our age, but are they as good? Steve Howell explores the Akai VX90 and provides some guidance on how it can be used with Akai's range of sampling machines.

Steve Howell tries out Akai's VX90 synth expander module and discovers what it can do when you connect various sampling machines to it.

One of the things that originally attracted me to synthesizers was their expandability, especially the early modular variety. If you felt like adding a few oscillators or an extra filter, or whatever, you could do so easily and economically - heck, you could even mix modules from different manufacturers and create a system which used (stable) ARP oscillators, the famous Moog filters, and punchy Oberheim envelope generators and VCAs. If you were up to it, you could even incorporate your own designs into the instrument. Modular synthesis, therefore, is a highly flexible method of sound creation that I believe still remains unequalled by many modern synthesizer designs.

The advent of programmable polysynths in the mid-Seventies rather knocked all this on the head as the Prophets and Oberheims were very much self-contained instruments with little in the way of interfacing facilities. Then, of course, came MIDI, which has allowed us to return to a form of modular synthesis where you can combine sampling, FM, analogue or digital synths virtually in any permutation.

Of course, the cheapest way to build such a synth system is to use keyboardless expander modules - after all, why waste money on extra keyboards if you already have one capable of doing the job! Technology has advanced to such a degree that the synthesizing capacity of Rick Wakeman's or Patrick Moraz's keyboard arsenal can, today, be fitted conveniently into one or two 19" rackmounting expander units.


One such expander is the VX90 from Akai. This is a keyboardless version of their AX73 polysynth and offers a fairly basic 'Junoesque' voice architecture of one VCO, one VCF, one HPF (High Pass Filter) and one VCA per voice. Unlike the Juno, however, it has two envelope generators and a far more useful LFO though it does also have a built-in chorus function.

What is unusual in this hi-tech age is the fact that the VX90 employs voltage controlled oscillators (VCOs) instead of the more common DCOs (digitally controlled oscillators) found on most modern designs. Now some would argue that DCOs don't produce such a 'warm' sound as good ol' VCOs. The latter are well known for wandering out of tune slightly, and in a polysynth this can be a potential disaster area. It can also be an advantage...

You see, it is impossible to tune 'real' instruments (ie. non-electronic ones) to mathematical precision and it is this failing, if you like, that gives them 'warmth', 'character', 'vibrancy' - call it what you wish - and DCOs, with their rock-steady digital pitch stability, cannot recreate this. I think Akai's decision to use VCOs has been a good one as the VX90 sound does have a certain undefinable richness to it that seems lacking in other synths I have tried. The VX90 is particularly effective when layered over DCO-equipped synths or FM machines as the little tuning discrepancies add a lot to the overall sound. If the tuning wanders too much on the VX90, there is an [AutoTune] button that will recalibrate the tuning of all six VCOs. Interestingly, this function is transmitted over MIDI thus allowing other synths to be tuned remotely.

The VCOs feature a goodly selection of waveforms which include sawtooth, triangle, square/pulse and a sawtooth/triangle mix. There are pulse width modulation (PWM) controls as well but what is most interesting is that these controls don't just affect the square wave - they affect all the waveforms - which leads to the creation of some quite unusual sounds. As yet, I've not had the chance to look at them on an oscilloscope but they do sound very inspiring. There are two PWM controls - [Depth] and [Rate].

The LFO that controls the pulse width modulation is totally separate from the main LFO, which is good news, and also, if the PWM rate is set to '0', the [Depth] control then acts as a manually-operated pulse width control for setting a static offset on the selected waveform.

There is also a pink noise generator which can be balanced against the level of the VCO waveform.

The VCF is a fairly standard low pass filter and sounded like a 24dB/octave type (as opposed to the 'fizzy' sounding 12dB/octave variety favoured by other Japanese manufacturers). It offers the usual controls for [Cut-off Frequency], [Resonance], [Env Depth] (positive and negative going) and [Key Follow]. Unusually, though, it is also possible to modulate the filter's cut-off frequency with the selected VCO wave and this introduces interesting sidebands into the sound since it's performing a very basic form of FM (frequency modulation). As the VX90 only has one VCO per voice, the possibilities are restricted - with two VCOs some very serious noises could have been made - but, even as it is, you can create sounds you won't get from other comparably priced units.

The envelope generators (EGs) are the usual 4-stage ADSR types found on most synths and these can be assigned to sweep VCO pitch, VCF cut-off frequency and to open and close the VCA. It's a shame Akai didn't incorporate a more capable design, such as we find on the Juno or Ensoniq ESQ-1, but the bonus of having two EGs on the VX90 helps to overcome this. All in all, a fairly standard arrangement but very flexible. I suspect that the EGs are software-generated as the ADR slopes are very linear - I only wish we could return to having exponential slopes as these produce a far more natural characteristic. As it is, though, they do the job.

The VX90's LFO offers no less than five waveforms - rising and falling sawtooth, triangle, square and random - and these can be routed to modulate either the VCO, the VCF, or the VCA. I'd like to have been able to combine routings to a choice of destinations, but the arrangement's OK as it is, I suppose.

I'm pleased to say that the LFO is of the free-running variety which doesn't reset to the leading edge of its cycle with every new note played, making it ideal for slow filter sweeps. The LFO can either be permanently 'on', automatically delayed, or introduced via a Mod wheel. It's a shame aftertouch can't be used for this as I suspect that the VX90 will be used by owners of keyboards that have such a facility. Still, can't have everything I suppose.

Other features include the chorus unit and Assign mode. Both of these are ostensibly for beefing up sounds using detune effects. The chorus is a bit of a disappointment in that it's weak. It has three depth modes - off, 1 and 2 - none of which give the rich texture I have heard on other synths, though I wouldn't say that it's altogether useless - just subtle.

Three configuration modes are offered by the Assign function - Poly, Dual and Unison. 'Poly' gives you the straight six-voice polysynth, 'Dual' reduces the polyphony to three notes and layers the sound on top of itself, whilst 'Unison' assigns all six voices to one key. If you wish to offset the frequency of the voices in Dual and Unison modes you can do so with the [Detune] control to produce a wide range of effects, from subtle chorus (using small pitch offsets) to adverse discordancy. Also in Dual and Unison modes you have access to the variable portamento effect which can produce a range of glissando/slide effects. Unfortunately, Unison is not the usual single-triggering monophonic mode we have come to expect from most synths these days, but it can nevertheless produce some 'filthy' sounds!

Finally, it is possible to use the pitch bend wheel to bend the VCOs up or down a maximum of an octave. This wheel can also be used to open or close the filter, a particularly useful implementation of wheel control I wish other manufacturers would adopt as it allows for a great deal of expression. Brass and other swells are easily achieved with it, as are searing leadlines and expressive basslines.


The VX90 has provision for the storage of 100 sounds and those that come with it are generally of a high standard. Akai are also making available alternative cassettes of 100 sounds (there are two soon to be released giving a total of 300 sounds) if you want to expand your sound library. But editing is a very simple procedure and I see no reason why even novices can't get in there and personalise the factory sounds.

To edit, you simply press [Edit] and use the [BWD] or [FWD] buttons to get to the parameter you wish to alter, then you change the value using the data entry slider or the up/down incrementor buttons. Alternatively, you can enter the parameter number using the keypad - very simple and easier in my opinion than Roland's alpha dial system. Once you've edited or created a sound to your satisfaction, you can name it (up to twelve characters) and store it in any memory location you like (note: all the parameters described so far are programmable). You can also save the contents of the VX90 to tape which takes a few minutes. When loading sounds you can choose to load all 100 sounds or just a bank of 10, which is a nice touch. Sensibly, Akai have located the Tape In and Out sockets on the front panel, so if your VX90 is rackmounted you don't have to rummage around the back of your rack.

On the MIDI side of things, the VX90 can respond to velocity, pitch bend, mod wheel and patch changes, and can be set to receive on any MIDI channel (but not OMNI interestingly enough). There are the usual MIDI In, Out and Thru ports on the back panel but, sadly, there is no System Exclusive data available from MIDI Out.

All this in itself adds up to a modest but very capable unit that would not be out of place in anyone's set-up, however large or small, but there is one feature that I have purposely avoided that sets the VX90 apart from its competitors.


On the back of the unit you will find a 13-pin DIN socket. This is an external audio input that allows you to route the separate voice outputs that appear on a similar DIN connector on all of Akai's samplers through the VX90, where you can take advantage of the synthesizer's analogue processors. Being a six-voice synth module, this method is best suited to the S700, the X7000 or the now discontinued S612 samplers, although it is possible to process samples from an S900 if you put up with a few compromises.

Figure 1. Connecting an S700 sampler to the VX90 expander.

There is a special way of connecting the two units together, however, and a few things you have to do to get the system operational. Figure 1 shows an S700 rack sampler connected to a VX90, controlled by a master keyboard (which could, of course, be anything). You should note that the S700 is connected to the VX90's MIDI Out and not its MIDI Thru as you might expect. This is necessary because the VX90 does some MIDI data juggling which is actually transmitted to the S700 whenever a note is played. This happens automatically whenever you select [Sampler On] on the VX90. Now I don't know exactly what is going on inside the VX90 when you do this but it's not really relevant - simply connect the two units in this way and you'll have no problems.

Figure 2. Connecting a VX90 to an X7000 sampling keyboard.

Figure 2 shows the connection of an Akai X7000 keyboard sampler to the VX90. Note how, once again, the VX90's MIDI Out is used. When you use an X7000 in this way it is important that it is turned to the 'Logic Off' (Local Control Off) setting. What happens now is that the X7000's keyboard generates the MIDI note information and passes it to the VX90, which re-transmits it via the VX's MIDI Out all suitably 'scrunched' so that the X7000's samples are played correctly.

To connect an S612 rack sampler you should follow the diagram shown in Figure 1. In all cases, OMNI must be switched 'off' (this is very important). Once you've done that you can now start work.


One of the drawbacks with Akai's S700, X7000 and S612 samplers is the absence of onboard analogue processing facilities. But by hooking up any of these units to a VX90 you can filter samples and use the EGs, LFO, keyboard scaling and velocity control for a variety of tonal sweeps and modifications. You can 'shape' samples using the VCA and EG and you can mix the sample sounds with the VX90's VCOs - which is a handy way of disguising bad loops! You can also mix in noise from the pink noise generator and add stereo chorus to samples. That in itself makes the set-up very attractive but one feature that is very appealing is the ability to add a basic sort of FM to samples.

You'll remember that it is possible to modulate the VCF with the audio output of the VCO to create sideband frequencies - well, by routing samples through the VX90 and adding some VCO modulation, you can do this to samples. I'll admit it's not as capable as the Synclavier's method of adding true FM, but it's a source of much experimentation and some interesting sounds. The results are very dependent on the samples you feed through the VX90, of course, but it is possible to add a bit of 'rasp' to brass sounds and some 'scrape' to strings as well as some interesting metallic sweeps to other sounds. Add to this all the other processing possibilities and you have the means to transform sounds quite drastically.

You must remember, though, that what you are programming on the VX90 are only the parameters for processing the sample, and that when you save them you are not actually saving the sample itself - you must load the sample into your S700, X7000 or S612 whenever you want to use that 'sound' again. Not ideal for live work, I admit, but no problem in the studio.

Of course, because the main audio outputs from the sampler are still available, you can use those as well so that you can mix 'straight' and 'processed' samples together and, presuming that you are using some form of audio mixer, each of these can have different EQ and effects. So, plenty of possibilities despite the apparent simplicity of the design.

To use an S900 sampler with the VX90 is a slightly more complicated affair, however. You must connect it to the VX90 in the same way as the S700 but there is a lot more to be done on the S900 internally.

Firstly, you must copy every 'keygroup' in a program six times. I had it explained to me why you must do this but I can't quite remember the reason. So, rather than mislead you with duff information, let's just leave it at that. Having copied each keygroup you must then assign each one a separate MIDI channel (from 1-6) using the [MIDI Offset] page in the Edit Program. In other words, if you have a string sample with four keygroups you must copy keygroup 1 six times, keygroup 2 six times (and so on) and then, using [MIDI Offset], you must end up with a situation where keygroups 5, 9, 13, 17, 21, 25 are set to MIDI channel 1; keygroups 6, 10, 14, 18, 22, 26 are set to MIDI channel 2; etc...

It's a fairly complicated procedure, I'll admit, and one which eats up keyboards at an alarming rate. You can also run into some problems if you have more than a few samples loaded into the S900 as you'll reach a point where the internal memory is full and you won't be able to copy any more keygroups. Having done all that you must make sure that the 'global' MIDI channel is set to 1 and OMNI is 'off' on the master MIDI page. You can now take advantage of all that the VX90 has to offer.


So, there we are. This set-up is probably the first real modular MIDI system where, instead of simply layering sounds on top of each other or using the expander for multi-part sequencing, you can actually get into the guts of the expander for a more symbiotic (OK yaah!!) relationship between the two devices. Of course, if you do a bit of rewiring of the 13-pin DIN lead it might be possible to process other synths through the VX90 - anyone fancy filter-swept DX sounds?

It would probably mean a few compromises but I'm sure there is room for experimentation. Who knows, maybe manufacturers will take the lead from Akai (no pun intended!) and fit the 13-pin DIN (or its equivalent) onto their synths and samplers so that they can be processed in this way. I remember the fun I had routing string synths through my modular system years ago and it would be nice to get those sort of possibilities back again.

On its own, the VX90 is a nice little module. It's just a shame it isn't multi-timbral, as this would add a lot to its capabilities as an expander and as a sample processor. As an add-on to an S700 or X7000 sampler it opens up a lot of creative possibilities and can do a lot to personalise sounds. In these days of standardised presets, it's good to see a system that encourages experimentation (remember that?!!) in an affordable and easy to use package. Let's hope this is the start of a new way of thinking from manufacturers - after all, experimentation is what synthesizers are all about!

The VX90 expander retails at £549 inc VAT. Further details from Akai on (Contact Details).

Previous Article in this issue

The First Commission

Next article in this issue

Casio FZ-1 Sampling Keyboard

Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.


Sound On Sound - Jun 1987

Feature by Steve Howell

Previous article in this issue:

> The First Commission

Next article in this issue:

> Casio FZ-1 Sampling Keyboard...

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