Yamaha's SPX90 would be good value for money even if it only produced reverb and delay effects... but it goes on to do nearly everything.

When contemplating digital sound processors, it soon becomes evident that the main difference between one processor and another is simply a matter of software. Once the input signal has been digitised, the end result is achieved by mathematical processing and so the same box of tricks should be able to function as a digital delay, a reverb or even a fuzz box. Well, Yamaha have given the fuzz box angle a miss but their SPX90 can manage no fewer than ten different signal processing operations (with several variations on each), though not all at the same time of course.

In terms of sound quality, linear 16-bit encoding gives a dynamic range in excess of 75dB and the sampling rate of 31.25kHz means that all the effects have a 12kHz bandwidth. Both the input and output levels may be switched between -20dBm and +4dBm; signal distortion is quoted as being less than 0.03%.

As it stands, the unit has 30 preset programmes ready to go at switch on and there is room to store a further 60 of your own. You can also enter your own names for your effects. And it's got MIDI. As with the REV7, user programmes are created by calling up a preset effect and then modifying the available parameters so you don't ever have to start from scratch.

Construction

The SPX90 is an unassuming 1U rack mounting module and the front panel doesn't give much away. The only rotary control is the input signal level, all other functions being selected and modified by the keys located to the right of the display. The display itself is in three parts; the first part is a LED ladder input level display and this is followed up by a two digit numeric display which shows the memory number currently selected. Completing the display section is an illuminated LCD unit which displays the effect name and the parameter data value.

Also on the front panel are the Memory Trigger and Bypass jack sockets for use with optional footswitches. More of that later.

The back panel carries the MIDI In and Thru sockets as well as the signal ins and outs. Because some of the effects are stereo, there is one input and two outputs, all on unbalanced jacks. The operating level switches are also on the rear panel as is an 8-pin DIN socket for the connection of an optional remote control unit which looks to be identical to the one used with the REV7. The mains lead is captive.

Because this machine can do so many useful things, it's best to look at them all in turn rather than attempting to write a general overview so I'll kick off with reverb.

Digital Reverb

It would appear that the reverb features offered by the SPX90 are derived from those used in the highly successful REV7 but with fewer variations. Reverberation time is fully variable up to a maximum of 99 seconds and you can add up to 50mS of pre-delay. The first four preset effects are reverb treatments called Hall, Room, Vocal and Plate, so there is a reasonable variety. High frequency decay time can be independently varied and there are both high and low pass filters for further tailoring of the effect. Subjectively these reverb settings sound very much like those available on the REV7 though a longer decay time is available. All the reverb effects are mono in, stereo out.

An Early Reflection mode is included covering presets five and six but this is not strictly speaking a reverb effect as you can only use these initial reflections without the following main body of reverberation. There are four types on offer; Hall, Reverse, Random and Plate and these are useful for adding ambience without adding distinct reverb, 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 is also a low-pass filter covering the range 1 kHz to 11 kHz which is useful for taking excess brightness off the effect. The Reverse reflections create an interesting backwards reverb sound and the Room Size parameter (which controls the spacing of the reflections) determines the length of the effect. A specific reverse reverb effect is to be found at preset 17. These effects too sound like those provided by the REV7 and are sure to find a variety of uses.

Gated Reverb is catered for in a different section entitled Gate Reverb located in slot 16. The gate hold time may be set up to 30 seconds and the release time up to 32 seconds. In practice much shorter values would be selected if you want to produce the contemporary gated drum sounds but this does give scope for experimentation which is always a good thing.

"Of course this machine can only do one job at a time so you'll either have to record some of your effects directly onto tape or buy more than one SPX90..."

Delay and Echo

I must confess to being a little puzzled by the inclusion of both Delay and Echo modes as both appear to do much the same thing. They both offer independent control over the right and left channel delays with both positive and negative feedback being possible. The only difference that I can see is that Delay offers up to 500mS of delay whilst Echo has a maximum delay time of 250mS. In order that the echoes can be made softer in tone as they die away, the amount of high frequency feedback may also be varied.

The other DDL type effects such as chorus and flanging have their own sections and are not possible in this mode.

Despite the 12kHz bandwidth, the delay effects all sound quite bright enough for most purposes and the only real complaint is that the maximum delay time is not longer as 500mS can be a bit restrictive.

Modulation

Stereo flanging is the first modulation effect and this has all the usual parameters of 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. Chorus uses the same ingredients as flange except there is no feedback. In addition, amplitude modulation is included to give tremolo like effects.

Other modulation effects include Stereo Phasing, Tremolo (deep chorus) and Symphonic, the latter being a spatial enhancement chorus mode using similar parameters to flanging but without the feedback. All these effects are well up to the standard that you would expect from a good digital delay and the fact that they are in true stereo is a great advantage for studio use.

Pitch Change

If the SPX90 had no further tricks up its sleeves it would still represent excellent value for money. After all, what we've described so far is really just a stripped down REV7, but there's a lot more to come. Pitch Change is the effect that most people would describe as harmonising but as Harmoniser is a registered trademark of Eventide, it can't be called that. This setting allows you to change the pitch of any input by up to an octave in either direction in one cent steps and the output may be delayed by up to 400mS if so desired. Also, as this is a 2-channel device, you have the option of having a different pitch shift for each output and a MIDI keyboard may be used to control the amount of shift in real time.

If you do choose to operate in the 2-tone mode, this precludes MIDI keyboard control but if you only want a single pitch shift, you can use keyboard control and you can also add feedback for pitch spiralling effects. It must be understood that you don't play the pitch of the output from the keyboard but rather determine the amount of pitch shifting to which the input will be subjected and the system allows you to select a base key at which no pitch shift occurs.

"To my mind though, this processor is really aimed at the live performance market where its Jack of all trades virtues can be exploited to the full..."

Like all budget pitch shifters, the output 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 this setting is musically useful, particularly for slight detuning effects, and adding a pitch drop to a snare drum can be quite interesting. Pitch shifts of more than a couple of semitones do sound quite rough in isolation and so should be mixed with a generous helping of untreated signal for best results.

Freeze

This inauspiciously titled mode is in fact sampling, and although there's only a 500mS storage time, the sample can be played back under MIDI keyboard control. There are two modes of sampling, the first of which allows modification of the start and end points of the sample but does not permit keyboard control of pitch. This is useful for percussive sounds and the simple editing facilities are effective in making sure that the sample starts and finishes at exactly the right time.

The second mode allows no such editing but does give you keyboard control. Sampling can be initiated automatically by the sound itself or manually by pressing the Parameter Increment key and a trigger delay feature lets you trigger up to either 500mS before or after the input exceeds the triggering threshold. If this sounds impossible, it's easily explained by the fact that negative trigger delays are obtained by delaying the actual input signal somewhere inside the circuitry.

The sampling effects that are possible are somewhat rudimentary due to the lack of editing facilities and the limited sampling time but it is useful for short percussive sounds such as tuned bottles or metallic objects being struck. Trimming of the start and end of a sample is possible but not in the keyboard controlled mode.

Gate

Noise gates are usually analogue devices using voltage controlled amplifiers, but there's no reason not to do the job digitally if the hardware already exists for the digitisation and processing of an input signal. The gate included here is more akin to an ADSR envelope shaper found in many synths and so it may be used solely as a gate to clean up recordings or to impart a new envelope to existing sounds. The Trigger level or threshold is under user control and trigger delay may be effected if required for certain effects. Also a new function, Trigger Mask is included which prevents the device from retriggering until a user determined time has elapsed. The parameters are as follows: Trigger Level, 1 to 100%; Trigger Delay, -100 to 100mS; Trigger Mask 5 to 32000mS; Attack Time 5 to 32000mS; Decay Time, 5 to 32000mS; Decay level 0 to 100%; Hold Time 1 to 30000mS; Release Time 5 to 32000mS and MIDI Trigger may be either on or off. When on, the gate will trigger when any note is played on the MIDI keyboard, a useful feature if you need to apply a new envelope to a basic MIDI sampler such as the Powertran MCS1.

The only serious drawback to using this gate in a recording context is its limited bandwidth. Whereas 12kHz is perfectly satisfactory for delay effects where a portion of the original signal is to be added, it's too small for any serious processor designed to pass the whole of the audio signal. Neither is there a threshold LED to aid setting up as you would expect to find on a dedicated gate and setting up a gate using increment/decrement keys is ergonomically unsatisfactory. I would tend to treat this gate as a triggered envelope generator rather than as a gate in the traditionally accepted sense.

Compressor

Again, compressors are often analogue but this one offers independent control of Attack, Hold and Release times as well as allowing the user 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. Also the compressor may be triggered by pressing a key on a MIDI keyboard as well as the more convention mode of operation and the essential parameters are as follows: Trigger Level 0 to 100%; Trigger Delay 100%; Trigger Mask 5 to 32000mS; Attack Time 5 to 32000mS; Hold Time 1 to 30000mS; Hold Level 0 to 100%; Release Time 5 to 32000mS and MIDI Trigger may be on or off.

As with the Gate, this feature has been designed for the creation of special effects as well as corrective applications in recording but the same negative comments concerning the reduced bandwidth and the manner of setting the parameters apply here also. There's no parameter that tells you exactly what compression ratio you are setting up and you really do need a visual indication that the input is exceeding the trigger level.

"This product should not be seen as the pinnacle of achievement however as it is merely a taste of things to come."

Pan

Here's one that I didn't expect for a unit of this price but it does everything else so why not? Basically the autopanner will sweep a signal from left to right, right to left or alternately from one side to another in either a free running mode or triggered from the input signal or a footswitch. The signal triggered mode is the most exciting as pans can be synchronised to individual notes or drum beats and the pan speed is variable from 5mS to over half a minute. Once the signal exceeds the threshold, the output pans from whatever side it is resting at to the opposite side and the sweep rate may be set up by the user. Like the gate and compressor modes, there is a Trigger Mask facility which lets a sweep complete itself before retriggering is allowed though this may be set for any time up to 32 seconds or de-selected if not required. As with most of the other effects, the pan may be initiated by a MIDI note-on signal. This is a useful effect if not overused and I like panning echoes or reverb sounds without moving the original sound source. Of course you will need a second effects unit to do this as the SPX90 can only do one thing at any one time. One feature missing from this and many other MIDI devices is an input for a simple trigger pulse. It is most effective to use one of the trigger outputs on a drum machine to initiate a pan but with this system you have to use MIDI or the signal itself to set things going.

Vibrato

True vibrato or pitch modulation is catered for by the SPX90 and this includes a Delay parameter so that the vibrato can be made to develop over a period of up to 30 seconds. This may be initiated by the input signal for which a variable Trigger threshold is provided or a MIDI keyboard may be used to trigger the effect. All the usual vibrato parameters are accessible including speed, depth and vibrato rise time. Used on guitar or bass this effect is very tasteful and quite automatic but there is no reason why it should not be used to process signals off tape when mixing.

Parametric EQ

Another unexpected feature in a digital machine but I'm sure you'll find a use for it. 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 1 kHz whilst the low pass filter covers the range 1 kHz to 11 kHz. Both parametrics offer up to 15dB of cut or boost and their frequency ranges are 315Hz to 4kHz and 800Hz to 8kHz respectively. Bandwidth is variable from a Q of 0.5 to 5 and up to 400mS of delay may be added so that you can generate a sort of equalised echo. There is no feedback parameter though you could always add some using the controls on the desk. 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.

In Use

Though this is quite a mind boggling product, it is in fact very easy to operate and program. The parameter to be modified is selected using the Parameter key and then its value altered using the increment/decrement key. Actual memories or programs have their own increment/decrement keys and by this method a program may be displayed before it is selected for use using the Recall button. Likewise a new program may be committed to memory by using the Store key. Any effect set up may be selected either from the front panel or by MIDI patch change information in the range 1 to 128. For this purpose any MIDI channel between 1 and 16 may be used or, if preferred, the machine can be used in omni mode.

The only real difficulty is knowing which effect to use when you are mixing as you will invariably want to use at least three but be limited to only one.

Conclusions

There are aspects of this product that can be criticised but not reasonably so when its low selling price is taken into consideration. In spite of limited bandwidth, (not always a disadvantage anyway), such a wide range of different effects comes as a surprise. This product should not be seen as the pinnacle of achievement however as it is merely a taste of things to come. The day of the dedicated processor is drawing to an end and the new breed of machines will follow the same trends as home computers where one machine can do your accounts, play games and act as a word processor to boot.

As a reverb unit and as a delay the performance of the unit is well up to scratch though not quite as flexible as the REV7. Having a pitch shifter thrown in is really just icing on the cake and both the sampler and autopanner facilities should act as stimuli to the creativity of the user, even though they offer less than state of the art performance.

The maximum delay time really should be longer as should the sampling time but you have to make some sacrifices to keep the price down. On the other hand, it doesn't matter how cheap a unit is if all the effects are slightly substandard as no one will want it anyway but fortunately that criticism can't be levelled at the SPX90. The reverb stands up quite well as do the modulation effects and the DDL is fine in all respects but the maximum delay time.

The pitch shifter suffers the same problems as most budget devices offering the same facilities but it still useful if you apply it with care and the same is true of the sampler.

Of course this machine can only do one job at a time so you'll either have to record some of your effects directly onto tape or buy more than one SPX90 but I understand that Yamaha have nothing against this approach. If you already have a well equipped studio than an SPX90 would still make a lot of sense as an extra general purpose processor. After all it doesn't cost any more than most other programmable DDLs and it's a hell of a lot more flexible. To my mind though, this processor is really aimed at the live performance market where its Jack of all trades virtues can be exploited to the full and where the restricted bandwidth is less important. Keyboards are an obvious application but the new breed of MIDI controlled guitar amps should yield some interesting possibilities.

For the last few years we've been hearing nothing but DX7 this and DX7 that but by the time this year is through, I think that we'll be hearing just as much about the SPX90.

The Yamaha SPX90 costs £599.00 including VAT and further details may be obtained from Yamaha-Kemble Music (UK) Ltd, (Contact Details).