It looks like any other budget digital delay line, but thanks to some clever software writing, the Yamaha SPX90 is one of the most versatile signal processors yet designed, offering a whole host of facilities for the price of an 'ordinary' DDL. Outboard gear will never be the same again.

Take two digital effects processors - a reverb unit and a chorus, say. Open them up, look inside, and you'll discover that, if their electronic specifications are similar, the main difference between them is one of software. Once you've digitised an input signal, the things you do to it are all realised in arithmetic processing, so the same box of tricks can function as a reverb, a chorus unit, or even a fuzz-box. Yamaha have given the fuzz-box angle a miss on their new SPX90 effects unit, but despite this gross and disturbing omission, the machine can still manage no fewer than 12 different signal-processing operations, with several variations on each - though not all at the same time, of course.

In paper specification terms, the SPX90 uses linear 16-bit encoding, and has a quoted dynamic range in excess of 75dB. Sampling rate is 31.25kHz, and all the effects have a 12kHz bandwidth.

The unit has 30 preset programs ready to go at switch-on, and room for you to store a further 60 of your own, giving them appropriate names along the way. As with Yamaha's REV7 dedicated reverb, user programs on the SPX90 are created by calling up a preset effect and then modifying the available parameters, so you don't ever have to start from scratch.

In common with so many modern machines that use digital parameter access, the SPX90 has a front panel that doesn't give much away. A solitary rotary control covers input signal level, with all other facilities being selected and modified using a handful of function keys and increment/decrement (up/down) switches.

The SPX90's many functions can be split into different families of sound effects and treatments, namely Reverb, Early Reflection, Delay, Echo, Modulation, Pitch Change, Freeze, Gate, Compressor, Pan, Vibrato and Parametric EQ.

The reverb features offered by the SPX90 are derived from those used in the REV7 - though understandably, there are fewer variations this time. Reverberation time is variable up to a (silly) maximum of 99 seconds, and you can add up to 50mS of predelay to this.

The first four preset effects are reverb treatments called Hall, Room, Vocal and Plate, which give a reasonable variety. High-frequency decay time can be varied independently, and there are high- and low-pass filters for further tailoring. Subjectively, these reverb settings sound very much like those on the REV7 - clear, bright, and just a touch artificial, though not in any unpleasant way.

An Early Reflection mode is included, but this is not strictly speaking a reverb effect, as you can only use it without the following main body of reverberation. There are four types of initial reflection on offer - Hall, Reverse, Random and Plate - and all of them are useful for adding a discreet reverb ambience without yelling 'reverb!' at you; it's particularly effective on percussive sounds. The spacing and decay time of these reflections is under user control, and up to 400mS of pre-delay may be added. There's also a low-pass filter covering a range of 1kHz to 11kHz - useful for removing excess brightness from the effect.

"Reverb: There are four types of initial reflection on offer, and all of them are useful for adding a discreet ambience without yelling 'reverb!' at you."

There are also some Reverse Reflections, which create an interesting backwards reverb sound, again similar to that generated by the REV7.

Gated Reverb is catered for in a different section, predictably entitled Gate Reverb. Gate Hold time is adjustable up to a maximum 30 seconds, and the release time can be as long as 32 seconds. In practice, many users will select shorter values to produce those distinctive if rather passe gated drum sounds, but this extra range does give scope for experimentation, which is always a good thing.

Curiously, the Yamaha's Delay and Echo modes appear to do much the same thing. Both offer independent control over right- and left-channel delays, and both permit you to apply positive and negative feedback. The only difference is that Delay has a maximum delay time of half a second, whilst Echo effects only go up to 250mS. In order that the echoes can be made softer in tone as they die away, the amount of high frequency feedback can also be varied in both cases.

Setting function apart from composition, we find that Echo and Delay can only be used to generate repeat echoes. Other, modulation-based DDL effects such as chorus, flanging, tremolo and so on are not possible in either mode.

Despite the 12kHz bandwidth, the Delay effects all sound fairly bright, and the only real complaint is that the maximum delay time is not longer: 500mS can be a bit restrictive.

Stereo flanging is the first effect to come under the heading of Modulation, and offers all the usual parameters like modulation frequency, modulation depth, delay time and feedback. As the time delay increases in one channel it decreases in the other, giving a true stereo effect with a convincing sense of movement.

"Sampling: Maximum storage time is only half a second, so Ensoniq and the others aren't under much of a threat from the SPX90."

Chorus uses the same ingredients as flanging, except that there's no feedback. Other modulation effects include Stereo Phasing, Tremolo (deep chorus) and Symphonic, the latter being a lush, spatially-enhanced chorus treatment that uses similar parameters to flanging but, again, without the feedback. All these effects are up to the standard you'd expect from a DDL in the SPX90's price range, and the fact that they're in true stereo is a great advantage for studio use.

Pitch Change is the effect most people would describe as harmonising - though it can't be called that because Eventide would get cross. On the SPX90, it allows you to change the pitch of any input by up to an octave in either direction, in one-cent steps; the output can also be delayed by up to 400mS should you wish it. As this is a two-channel device, you have the option of selecting a different pitch shift for each output. If this isn't what you're after, you're given the alternative option of using a MIDI keyboard to control the amount of shift in real time - not by playing the pitch as such, but by selecting the amount of pitch-shifting to which the input signal is subjected, and by choosing a base key at which no pitch-shifting occurs. You can also add feedback and delay for pitch-spiralling effects.

Like all budget pitch-shifters, the output of this one gets rather lumpy when more than a little shift is introduced, which means that subtle detuning effects are fine, but fifths or octaves start to show signs of glitching. This manifests itself as an atonal modulation, making things sound slightly out of tune or metallic. Used with care, though, the pitch-shifting is musically useful, and adding a pitch drop to a snare drum, for example, can result in quite a novel sound.

Freeze mode turns out to be Yamaha's way of saying sampling. Don't get too excited, though: maximum storage time is only half a second, so Ensoniq and the others aren't under much of a threat from the SPX90.

In fact, there are two separate sampling modes. The first allows you to alter the start and end points of the sample, but doesn't permit keyboard control of pitch. The second mode allows no such editing, but does give you keyboard control via MIDI.

Sampling can be initiated automatically by the sound itself, or manually by pressing the Parameter Increment key. A trigger delay feature lets you trigger up to 500mS either before or after the input exceeds the triggering threshold, negative trigger delays being obtained by delaying the actual input signal somewhere inside the SPX90's circuitry.

"Compressor: There's no parameter to tell you exactly which compression ratio you're using, and you really do need a visual indication that the input is exceeding the trigger level."

The 'Gate' included here is actually more akin to the sort of ADSR envelope shaper common to so many synths, though without the 'S' bit. Thus it can be used solely as a gate to clean up recordings, or to impart a new envelope to existing sounds. You can vary the trigger level (or threshold), and invoke a trigger delay function similar to the one just discussed, except that the maximum time is only 100mS. There's another new function in Trigger Mask, which prevents the Yamaha from re-triggering until a user-determined time (in this case somewhere between 5 milliseconds and 32 seconds) has elapsed.

As far as the envelope shaper goes, Attack Decay and Release times are all variable between 5 milliseconds and 32 seconds, while Hold time can be as little as a millisecond. Decay level is also variable.

There's also a switchable MIDI Trigger facility. With this switched on, the gate triggers when any note is played on the MIDI keyboard - useful if you need to apply a new envelope to a MIDI sampler such as the Akai S612.

Using the gate in a serious recording context can be a problem, though, thanks to limited bandwidth. Whereas 12kHz is satisfactory for delay effects where a portion of the original signal is to be added, it's too small for any processor designed to pass the whole of the audio signal. Ergonomically, setting up a gate using increment/decrement keys isn't a lot of fun, and there's no threshold LED to help you, either. The SPX90's gate, then, is more usable as a triggered envelope generator than as a gate in the traditionally accepted sense.

Like gates, compressors are often analogue devices, but Yamaha have succeeded in writing some suitable software instructions for the SPX90's electronics to carry out. Thus, the compressor section offers independent control of Attack, Hold and Release times, as well as allowing you to set the operating Trigger threshold and the Hold level. Both positive and negative Trigger Delay times can be programmed, again by delaying the input signal when required. The Compressor can also be triggered by pressing a key on a MIDI keyboard, in addition to the more conventional mode of operation.

In the same way as Yamaha have seen fit to make the SPX90's version of a Gate useful as special-effects generator, so the Compressor can create a few fireworks of its own, in addition to operating in its traditional, corrective manner. Only trouble is, the Compressor suffers from the same limited bandwidth and ergonomic problems that beset its near neighbour. There's no parameter to tell you exactly which compression ratio you're setting-up, and you really do need a visual indication that the input is exceeding the trigger level.

"Autopanning: So long as you don't overuse it, this is a useful effect, particularly striking when used to pan echoes without moving the original sound source."

The Pan section hides an autopanner that sweeps a signal from left to right, right to left or alternately from one side to another - depending on whether it's in its free-running mode or set to be triggered from the input signal or optional footswitch. The signal-triggered mode is the most exciting, as pans can be synchronised to individual notes or drum beats; pan speed is variable from 5ms to over half a minute. Once the signal exceeds the threshold, the output pans from whichever side it's resting at to the opposite side. Like the Gate and Compressor modes, the Pan section includes a Trigger Mask facility which lets a sweep complete itself before re-triggering is allowed: this may be set for any time up to 32 seconds, or deselected completely if not required. And as with most of the other effects, the Pan may be initiated by a MIDI note-on signal.

So long as you don't overuse it, the Pan is a useful effect, particularly striking when used to pan echoes or reverb sounds without moving the original sound source. Bear in mind, though, that you'll need a second effects unit to do this, as the SPX90 can only do one thing at a time.

And so to the Vibrato section. All the usual vibrato parameters are accessible, including Speed, Depth and Rise Time. There's also a Delay parameter so that the vibrato (or pitch-modulation) can be made to develop gradually over a period of up to 30 seconds.

Finally, we come to the last stop on our journey through the SPX90's myriad functions: the Parametric EQ. This consists of two fully parametric filters, a high-pass filter, and a low-pass filter. The high-pass filter has a 6dB-per-octave slope, and is variable from 32Hz to 1kHz, whilst the low-pass one covers the range 1kHz to 11kHz. Both parametrics offer up to 15dB of cut or boost, and their frequency ranges are 315Hz-4kHz and 800Hz-8kHz respectively. Bandwidth is variable, and up to 400mS of delay can be added so you can generate a sort of equalised echo.

For serious use, a parametric filter with a 12kHz frequency response makes no sense whatsoever. But it can be used to good effect on electric guitars and other instruments that have little or no really high-frequency content, or if preserving the original signal's bandwidth isn't of paramount importance anyway.

You could be forgiven for reading through that list of functions and facilities, parameters and possibilities, and thinking, at the end of it all, that the SPX90 is an utterly mind-boggling instrument that takes an eon-and-a-half to get acclimatised to. But you'd be wrong. As digital-access devices go, this one is quite easy to operate and program. It's not an ideal state of affairs, having just a central panel of switches with which to do everything, but on a machine as multi-layered and multi-faceted as the SPX90, there's no realistic alternative. And in any case, the system only becomes a hindrance (as opposed to a nuisance) in the Gate and Compressor modes, as mentioned earlier.

"Conclusion: Before this machine appeared, you had to buy four or five outboard devices to get the same versatility — and that could work out at the price of two SPX90s."

Cramming so much into so little a space (and at so low a price) obviously has its drawbacks. But overall, you'll be consistently and pleasantly surprised by the SPX90's overall performance, so long as your expectations aren't sky-high. Yamaha have realised that it isn't enough simply to endow a machine with a load of functions, none of which it can execute properly. Thus the SPX90 performs very respectably in most areas - just as well, in fact, as just about any other DDL in its price category, regardless of the number of musical options on offer.

Even where its capabilities are limited by restricted bandwidth (Gate, Compressor, Parametric EQ) or sample time (Echo, Delay, Sampling), the new Yamaha succeeds in offering sufficient variable parameters to make each section a useful stimulus for creative signal processing, outside what would normally be considered as 'state of the art' performance.

On the interfacing front, Yamaha have been thoroughly modern and gone for MIDI above all else. If you don't want to trigger the effects from MIDI, most modes let you use the footswitch input to do the job - but I'd still like to see a dedicated trigger pulse input for drum machines and monosynths. MIDI may be the standard where polyphonic synths are concerned, but for simple triggering (and especially for things like auto-panning), the humble pulse is more practical.

MIDI is useful when it comes to patch selection, though. Any effect, preset or user-programmed, can be selected by MIDI patch-change information in the range 1 to 128. Any MIDI channel between 1 and 16 may be used for this purpose, and the machine can also be used in Omni mode.

Those facilities are at their most useful playing live, where remote, instant access of programs can come in really handy - even more so when MIDI-controlled combo amps become widely available. The SPX90's restricted bandwidth won't be as noticeable at a gig as it is in the studio, either.

Overall, it's tempting to look at the SPX90 and conclude that it's the pinnacle of digital signal-processing achievement. For the time being, that's exactly what it is: the first effects unit to take full advantage of the flexibility of computer technology, using the same electronics to perform a multitude of different software tasks. In some ways, this revolution has been a long while coming to the outboard effects sector; synth players and sampler users have been enjoying its benefits for years.

But there's a second stage of that revolution which has still to make its presence felt in the music industry. For whereas machines like the SPX90 can only accomplish one task at a time, many of today's home computers have sufficient memory and processing power to accomplish several - multi-tasking, in other words. The SPX90 may be clever enough to do the musical equivalent of a home micro's game-playing, accounting, and word-processing jobs, but unlike the most recent computers, it can't do all of them simultaneously.

This shortfall poses something of a dilemma in the recording studio, where reverbed compression, pitch-shifting echoes and so on aren't possible with the SPX90 unless you do one of two things. One is to record each instrument with the first treatment already applied to it, leaving the second layer of processing to the mixing stage. The other is to buy more than one SPX90, which isn't quite as silly as it sounds. Before this machine appeared, you had to buy four or five different outboard devices to get the same sort of versatility - and that lot could add up to over a grand, or about the price of two SPX90s. And I understand that Yamaha, for their part, have no objections to anyone buying more than one SPX90.

Price RRP £599 including VAT

More from (Contact Details)