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Yamaha REX50

Article from Sound On Sound, February 1988

Martin Russ reveals the hidden features of Yamaha's budget digital multi-effector and explains how it can be coaxed into supplying more than one effect at once.

It is under a year since the REX50 was announced - and at the time many people dismissed it as just an SPX90 Mk1 in a different box. Always on the look-out for a bargain, I bought one more or less straight away since, at £365, it cost less than the Mark I SPX90s which were being sold off at the time to make room for the incoming MkII. Since buying it, I have been busy exploring its potential - so now seems like a good time to report on the results so far. OK - so I got a cheap SPX with built-in distortion, but what is so special about that? Read on and you will discover that there is rather more to the REX50 than the advertising and even the manufacturer's documentation might suggest - yes, it's time for some 'undocumented' features! [see panels- Ed.]


But first, an overview of the history of budget digital effects units by the big Y.

All of their reverb and delay units are a direct result of the enormous investment made by Yamaha in developing its own VLSI chip production facilities, especially in connection with the design of Digital Signal Processing chips (DSPs). The first unit I encountered was the R1000, a simple, four preset reverbs-plus-parametric EQ 1U high box, closely followed by the D1500 - the world's first MIDI-compatible digital delay line (you could remotely select one of the 16 memory banks with a MIDI program change command!). In the professional arena, there were the REV1 and YDD2600 reverb and delay units: big, comprehensive and expensive, but using the same basic digital signal processing technology.

Early in 1986, the offspring ot all this activity was released onto a mostly unsuspecting world - the SPX90. Affordable, high quality, MIDI-compatible, with 13 basic effects covering all the DDL effects you could think of, as well as a few others like parametric equalisation, panning, compression and gating - not surprisingly, the SPX90 was an enormous success.

Exactly a year later, the SPX90 was updated to the Mark II version, with longer delay times and a few improvements to parameter ranges, etc. Hot on its heels came the REX50, a small, distinctively shaped box (I've heard it called 'the Hoover' by several people) which was tentatively described as an SPX90 Mk I with distortion added for guitarists. So what do you get for your money?


Yamaha describe the REX50 as a 'digital multi-effector', meaning that it can produce a large number of audio effects singularly, rather than several effects simultaneously. In fact, as we shall see, there are a few cases where you can obtain more than one effect at once, but you cannot combine reverb and echo, or early reflections and reverb; if you want this sort of combined effect then a second REX50 or the REV5 [reviewed SOS Nov '87] should provide the answer. Remember that for the price of a REV5 you can buy about 3½ REX50s!

There are 9 major types of effects available:

  • Reverb: 4 types - Hall, Room, Vocal and Plate.
  • Early Reflection: 4 types-Hall, Random, Reverse and Plate.
  • Delay and Echo: with either separate or combined feedback.
  • Modulation: 4 types - Flange, Chorus, Phase and Symphonic.
  • Pitch Change: 3 types - MIDI controlled with feedback; 2 pitches in stereo or mono.
  • Gate: a noise gate/envelope shaper and gated reverb.
  • Compressor: a delay and compressor.
  • Pan: auto-panning.
  • Distortion: basic 'overdrive' distortion plus nine combinations with reverb, delay/echo and modulation effects.

30 presets are stored permanently in ROM and give some idea of the scope of the basic effects. 60 RAM-based memory locations (with battery backup) are provided for storage of your own variations.


The incoming audio signal can be either mono or stereo, although the two channels of the stereo signal are summed before the digital processing. A rotary control on the rear provides adjustment of the input gain. The unbalanced output is in stereo, with a switch to select either effect-only or effect-plus-input, so you can use the REX50 in-line or as an outboard effect using the send and return connections on a mixer.

All audio levels operate at the home studio standard -10dBm level, with a 10Kohms impedance. The left channel input is the mono input, and if you connect only this then the direct signal appears at both outputs. Rather than the usual 'home recording standard' phono/RCA connectors, the REX50 uses quarter-inch jack sockets for the audio input and output connections, presumably because of its intended application as a guitar effects unit.

Digging out my rather ancient custom-built guitar (from my 'aspiring guitar hero' days!), I discovered that the input of the REX50 is rather insensitive when used with single-coil or low output level pickups, and I only achieved acceptable performance with humbucking (high output) pickups or 'active' guitars. So for the best dynamic range and lowest noise floor, it looks like some sort of preamp is recommended to use this unit with guitar, although the effects loop of most guitar amps may suffice (using the REX50 with a single combo amp rather defeats the purpose of the stereo outputs!). In contrast, the levels were OK with the REX connected to my multitracker, and my keyboards and expanders.


Once inside the REX50, the audio signal is converted to digital using some very clever technology which thoroughly exploits Yamaha's expertise in designing chips. They use a single digital-to-analogue convertor (DAC) chip to perform the analog-to-digital conversion, as well as the stereo digital-to-analogue conversion, multiplexing between each function. So, for the price of a DAC and Yamaha's LSI control chip, you get an ADC and two DACs.

The quantisation is 16-bit linear at a sampling rate of 31,25kHz, which gives a resultant frequency response of 20Hz to 12kHz (limits of 1dB up or 4dB down at 12kHz is the specification in the service manual, referenced to 1 kHz), with a maximum harmonic distortion figure of about 0.1 % at 1 kHz. The noise floor in 'Bypass' is specified as less than -76dBm, and there is a servicing adjustment to optimise this. Yamaha specify a dynamic range of 74dB for the effect signal and 80dB for the direct signal, and I found the overall performance to be of the high quality which all the above figures suggest.


The effects are all of high quality as well. All 30 presets are set up with the effect balance at 100% (all effect) and so need the 'effect-plus-direct' back panel switch setting for in-line use. Before the SPX90, one might have expected a mix of excellent, merely OK, and rather indifferent effects from a multi-effect unit, but since then consistent excellence seems to be the order of the day. The REX50 continues this precedent: the reverbs are natural sounding (although for an 'artificial' reverberator like a 'plate reverb', I am unsure as to what natural means!) with no unexpected colouration or nasty quantisation effects. The Early Reflection program provides a convincing acoustic simulation of a room, without the mushiness of reverb. The Gated Reverb produces the slightly cliched, familiar sound and needs to be used with care - drums sound fine, but... The times and feedback levels for the Delay and Echo presets are independently adjustable for the two channels, but the maximum times are rather short (500ms for Delay, 250ms for Echo).

The Flange, Phasing, Chorus and Symphonic presets all do exactly what their names suggest, and are very effective at producing the 'modulated delay' type effects. The Reverse Gated Reverb is a very effective special effect giving an impression of backwards echo or reverb. The Pitch Change presets offer all the Daleks, Donald Ducks, instant arpeggios and harmonising effects you could want.

The above effects are all variations of 'digital delay line' type effects. The remaining REX50 effect programs suffer from the limitation of only having a 12kHz bandwidth and so lose some of their usefulness. The Compressor works well and serves as a nice introduction to the creative use of compression and limiting. The ADR-Noise Gate is slightly more obscure in its application - gates are often employed to quieten the output of noisy effects pedals; or it could be used for controlled muting of audio signals via MIDI. The Pan preset is the final effect in the non-distortion set and sweeps the sound between the left and right channels at any speed you like. Personally, a triggered pan would have been much more useful - so I created one (see panel text for more details).

The final 10 presets all feature the digital distortion, either on its own or combined with other effects. There are four variations on Distortion with Reverb, Distortion with Delay or Echo, and Distortion with Flange, Chorus or Symphonic. In each case, the amount of distortion and the effect balance can be altered to suit. The Distortion-only preset and the Echo/Delay combinations also allow some control over the tone of the distortion. Opinions of the distortion effect itself varied amongst the guitarists I consulted - this is a very subjective area - so try one out and decide for yourself.


You can use MIDI Program Change messages to remotely select any REX50 effect, as well as set the pitch shift of one of the three Pitch Change options and trigger the Gate effects. You can map the incoming Program Change messages to the 90 memories in the REX50 using four independent banks, each covering the 128 possible Program Change messages. So you could have a normal mapping (where program 1 = memory 1, program 42 = memory 42, etc) and use the remaining three banks for particular instrument combinations. I'm not sure if I would rather have had the memory allocated to longer delay times, or perhaps a MIDI System Exclusive command to load in and save banks of maps. As it is, there are no System Exclusive messages, so you cannot change REX50 effect parameters via MIDI, nor store and load memories - a great pity. You can select MIDI Off, Omni or a Channel for reception and that is it - the MIDI implementation chart is mostly empty.

For part of the answer to why the MIDI implementation is so sparse, you only need to look at the REX50 back panel - there is only a MIDI In socket. Actually, there is very little room left on the back panel. Apart from the audio input and output jacks mentioned above, there are two additional jack sockets for two footswitches - a Bypass footswitch and a memory increment switch which can be used to select effects. A range selection feature enables you to choose the memories which this switch will advance through, making it very useful for live performance (guitarists take note). Also on the back panel is the mains lead inlet and the mains switch; in common with other Yamaha pro-audio equipment there is an onboard power supply, so you don't have to worry about losing mains adaptors or treading on their fragile and tiny connectors. An IEC socket for the mains would have been even better, but there isn't really enough room!

What about the front panel? Well, you get a non-backlit LCD readout, which shows you the name of the currently selected memory and any parameters, etc. The only indication you get for the Bypass condition is a flashing 'B' in the top left-hand corner of this display, which is not visible in low light conditions and a LED would have been much better (you should be able to hear if it is bypassed, of course!). A bright, easily read LED display is used to show you the number of the current memory and a three section (-20dBm, -10dBm and Clip) LED input level monitor is provided. All other controls are accessed using just eight pushbuttons (another from the FB01 designer?).

Despite this alarmingly small number of buttons, it is very easy to use the REX50, and I am almost inclined to think that more buttons would detract rather than improve the usability. To access a memory, you press the MEMORY button and then use the up and down arrows to step through to the required effect. Pressing the RECALL button activates that effect. To edit the parameters you press the PARAM button repeatedly to choose the parameter and then use the up and down buttons to change the value. There is a dedicated BYPASS button which does exactly what you might expect. Accessing some of the UTILITY button's functions requires careful selection, and some additional legending on the front panel would have helped here. At any rate, the buttons fit into the overall design of the REX very nicely.

It is a pleasant change to find a piece of cost-effective hi-tech gear which is stylishly and effectively designed. Inside, a single PCB is used with all the components mounted directly on it - a combination of conventional thru-hole and surface mount. The metal case, which is hidden beneath the plastic exterior casing, is used as a heat-sink for the voltage regulator and the buttons are a moulded part of the case itself, not separate.



Freq Response: 20Hz to 12kHz (+1/-4dB, 1kHz = 0dB)
Sampling Rate: 31.25kHz
Quantisation: Linear, 16 bits
Dynamic Range: 74dB (effect)
Noise Floor: -76dBm
60 RAM memories
30 preset effects
4 banks of MIDI program change mapping
Stereo Input and Output at -10dBm
MIDI In only

If you thought that multi-effects units had reached their logical conclusion with the SPX90, then the REX50 must have come as quite a surprise. At the price there are only a few dedicated reverbs for competition and certainly nothing with the control over a wide range of effects as the REX50. The addition of built-in distortion makes the REX50 a contender for the guitarist's effects armoury (possibly replacing almost everything else!) and it is certainly an indispensable tool for the home recordist. There is a great deal of scope for imaginative use of the available facilities, particularly on drum sounds and rhythm tracks.

Overall, this is a wonderful box for creating just about any acoustic environment you care to mention, from the natural to the impossible. The ultimate accolade from a reviewer is to say that he bought one - well I did! (I now have a slightly under-used effects rack in my studio and a REX50 permanently coupled to the MIDI network in the keyboard area.)

Price £365 inc VAT.

Contact Yamaha-Kemble Music (UK) Ltd, (Contact Details).


There are several differences between the REX50 and the SPX90 Mk1. Here is a summary of the major ones:

Table-top 1U rackmount
10Kohms 0/P 600 ohms O/P
<0.1 % Distortion <0.03% Distortion
Optional remote
- MIDI Thru
- Switchable in/out levels
3-LED meter 7-LED meter
- Backlit LCD
(see panel) Triggered Pan
- Freeze (sampling)
Delayed Vibrato
8 buttons 11 buttons


Chorus using Pitch Change:

One of the standard tricks with pitch changing is to use it for 'chorus' type effects. Use PITCH CHANGE B for mono chorus, PITCH CHANGE C for stereo chorus.

First one suitable for Piano:

1 Pitch: +0
1 Fine: +8
1 Delay: 0.1ms
2 Pitch: +0
2 Fine: -10
2 Delay: 0.2ms

And now one for Strings and Pads:

1 Pitch: +0
1 Fine: +12
1 Delay: 0.1ms
2 Pitch: +0
2 Fine: -16
2 Delay: 10.0ms

NB. Balance and Output Level should be set to your own preference.

EQ Tricks - Preset 21:

You can use Distortion preset 21 to give Equalisation without Distortion. Set the Distortion parameter to 0% and you can now use the three EQ parameters to change the tone of your sound. The sound will now not be passing through the distortion section and so you get only the effect plus the gate. The two remaining parameters enable you to access the noise gate built into all the Distortion-based effects.

Gating Effects:

By exploiting the Gate at the output of presets 21 to 30, you can create all sorts of treatments not possible with the other types of effect. Turn off the Distortion parameter (set it to 0%) and then try setting the Trigger Level to somewhere between 80 and 90. An input signal of about -10dBm on the LEDs will trigger the effect, lower sigmals will not.

Using a velocity-sensitive keyboard, you can now bring in an effect merely by playing slightly harder - you will need to experiment a little to find a suitable combination of level and trigger.

With non velocity-sensitive synths, it is easy to set the Trigger Level such that it does not trigger for single notes, but does for two or more notes. This can be very useful in solos and performances, where you can add echoes or reverb to just the notes you choose from the keyboard, without any need to break your concentration and grope about on the floor for a footswitch.

Using a drum machine with programmable output levels or accents, it is possible to set the triggering so that it only works for the loudest drums. Thus, it is possible to have the rest of the drums passing unmodified through the REX50 (choose the Effects-plus-Direct switch setting) with Gated Reverb only on the drum you want. This means that you do not need a drum machine with individual outputs!

Triggered Pan:

Depending on the way you connect the REX50 to a mixer/multitracker, you can use the Gate/Trigger effect already described for presets 21 to 30 to obtain all sorts of effects which are theoretically 'not possible' on the REX50!

By splitting the input into two and feeding one signal directly to the left channel and the other through the REX50 to the right channel, you can use the loudness of the incoming signal to trigger a pan to the centre of the stereo image. This is very effective on drum sounds or bass lines. Try using a very simple effect (just an increase in level will work - use the Output Level parameter and set the modulation in the chorus to 0, for example).

By using echoes in such a triggered pan set-up, it is possible to have echoes of only the loudest sounds appear in the centre of the stereo image, whilst everything else is unaffected. Once you start using the extra possibilities provided by the Distortion-plus-Effects programs, you will quickly discover a wide range of other effects, most of which are not possible on an SPX90 and are even quite difficult to set up in a whole rack of outboard gear! Have fun!

Instant Tangerine Dream:

An old trick this, but well worth mentioning. By using extreme room sizes and long delay times, you can effectively lower the density of the early reflections and produce just a couple of syncopated echoes. By choosing your timings carefully you can exploit the stereo nature of the reflections and have one echo on one side, and two on the other! Try putting a simple repetitive sequence into the REX50 and experiment with tempo settings.

Type: Random
Room Size: 11.8
Liveness: 10
Delay: 400ms
LPF: Thru

Drum Toasting:

Fed up with your drum machine's ROM based sounds? Try altering the sounds with your REX50.

Pitch: +12
Fine: +0
Delay: 21.0ms
FB Gain: 73%
Base Key: Off

...or this one:

Pitch: -12
Fine: +0
Delay: 0.1ms
FB Gain: 77%
Base Key: Off

NB. Cymbals are particularly suitable for this sort of tweaking.

Chorus, Reverb and Slapback Echo!

You can obtain three effects at once if you try this:

L Pitch: +0
L Fine: +12
L Delay: 30.0ms
R Pitch: +0
R Fine: -13
R Delay: 10.0ms

Also featuring gear in this article

Previous Article in this issue

Ensoniq SQ-80

Next article in this issue

Customising Synth Patches

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

The current copyright owner/s of this content may differ from the originally published copyright notice.
More details on copyright ownership...


Sound On Sound - Feb 1988

Gear in this article:

Studio/Rack FX > Yamaha > REX50

Gear Tags:

Digital FX

Review by Martin Russ

Previous article in this issue:

> Ensoniq SQ-80

Next article in this issue:

> Customising Synth Patches

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