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Cause & Effects

Jez Ford is seriously effected by Digitech's latest signal processor - the DSP-128

Jez Ford gives the DigiTech DSP-128 the once over.

The DigiTech DSP-128 Plus comes onto the market in direct competition with the Alesis Quadraverb. The two units are superficially similar - both MIDI controllable, multi-effect 16-bit digital signal processors with the ability to chain four separate effects in series simultaneously.

Alesis has the advantage that people have been proclaiming with delight over its last few offerings - namely the MIDIverbs and Microverbs - and the Quadraverb got the trumpet heralding that which such a reputation can command.

DigiTech has its own reputation, and very good it is too, but to break the virtual monopoly of public opinion that Alesis has been commanding will be no mean feat. It will need to find an edge over those chunky buttons and trendy black frontage on the Quadraverb. Will it, won't it? Let us see.

Buttons and Lights

The DSP-128 Plus comes as a 1U rack in grey steel finish with a bright red LED alpha-numeric display (which removes any problems of reading from odd angles that can occur with LCD displays). You cycle through the preset patches by up/down cursors, and through the parameters of each effect with the adjacent left/right cursors. There are 128 preset effects. These are not named as they are on the Quadraverb but are referred to simply by number. This is a pity, since nothing can identify a patch for a song called 'New York', for example, quite as easily as naming the effects patch 'New York'. Then again, as any synth user will tell you, it doesn't take long before the numbers fix in your mind as the patch sounds themselves.

In addition to the alpha-numeric display, DigiTech has added 12 LED lights on the left of the panel to show which type of effects have been chained into each patch. In many ways this surpasses the utility of a name - on the Quadraverb the limited number of characters available leads to names like 'DTUNE-SPRD-RVB'. No such abbreviations are necessary with the LED display on the DSP-128 Plus.

The preset patches are about what one would expect from a high-quality 16-bit processor - very quiet (s/n typically 88dB) and with excellent use of the stereo outputs for some wide-panned reverbs. The patches are divided up into types basically by room size, with variations on each theme using chorus, flange and delay. Gated reverbs follow, with various straight hall reverbs, some great multi-tap stereo delays and lastly a selection of handy parametric and graphic equalisers.

Patch Working

Programming new effects in the unit must be approached with caution since there is no buffer that keeps the factory original while you edit - no compare facility. You can return the entire unit to its presets but then everything you've ever done is wiped. Those with a computer would be strongly recommended to dump the lot to disc on MIDI systems exclusive whenever you make a change that you think will be a permanent one.

As suggested by the 12 LEDs on the front panel, there are 12 basic effects available. These can be chained together as algorithms. There are 14 of these in total to choose from. Statistics fiends will point out that this would seem not to allow all possible combinations to be followed but this is only because some of the 12 effects (graphic equalisation for example) use everything the processor has got and cannot be chained up. My personal taste in effects units inclines towards the 'whopping great reverb' sound that I consistantly swamp all my mixes with, give me the MIDIVerb II and I go straight to '27', a Quadraverb and I go to '66'. Huge sounds that could make a sawtooth sound like Mantovani. So I was interested to see how the reverbs in the DSP-128 Plus were put together.

The Ultimate Reverb

The first three effects, large room, medium room and small room, are all prepackaged reverbs to be chained with other effects. They are excellent reverbs but the tweakable parameters are limited to low-pass filtering, reverb level and the reverb decay time. If you need more control, you need to switch to algorithm 13, which DigiTech has modestly entitled "The Ultimate Reverb". The reason for such pomposity is clear.

With this algorithm you can fine-tune an effect to a remarkable degree. You can specify separate delay rates and diffusion ratios for initial bounces and subsequent delays, reflectivity figures, room width and so on.

The degree of control is far greater than that normally offered and the explanation of each term in the manual gets your brain buzzing with the rudiments of acoustics and sound propogation. And since this lets me design even bigger and thicker reverb patches, I approve wholeheartedly.

Because of the LED alphanumeric display, editing is not quite as simple as it might be. From the patch number, you scroll left or right along the full list of parameters. While this makes it easier for the processor to simply track along the memory EPROM's addresses, it would have been clearer to page through the parameters. The limited number of characters also means that each parameter has a two letter code that has to be checked in the manual. Once you have found the chosen parameter however, it is an easy task to achieve the required result.

MIDI Controllers

This next option is perhaps the most versatile on the whole processor and one of which all MIDI equipment manufacturers should take note. In the great book of MIDI there is a list of MIDI controllers, numbered 0 to 127. These are part of the MIDI messages that are transmitted to affect sounds. Messages starting with control code 1, for example, affect the modulation. These will be transmitted whenever you tweak the modulation wheel of a master keyboard.

As a bit of bonus versatility, DigiTech has deemed that any variable effect parameter can be assigned to any MIDI controller. Well get down and boogie - this is powerful stuff! Bung reverb level onto controller 1 and delay time onto controller 2 and you can vary these parameters mid-solo, from mod wheel and breath controller respectively. For live work this can be invaluable and is way preferable to stepping through patches with a foot pedal. It is particularly handy since most of us are already used to using these controllers on the fly. But... (yes there had to be a but...) these changes are global and irreversible. Global meaning that if you alter the delay time in this way, every patch containing delay will have that parameter permanently altered. Irreversible meaning that there is no button to press to get it back where it was. Oh whoops! Slap hands DigiTech. This makes it a pretty risky tactic to adopt unless you're happy to reboot the whole unit back to the factory presets between songs (see what I mean about dumping regularly to computer?).

MIDI IN and OUT Systems exclusive messages are limited to dumping the whole set of patches either to or from the DSP-128 Plus. It's a pity you can't program it via MIDI, especially given the small scrolling display problems there are when going in via the front panel. You could allocate each parameter to a different MIDI controller, select the algorithm by MIDI program change messages (which are recognised) and totally revamp the entire internal memory for each effect - but this would be a little drastic.


This is a very clean unit capable of powerful and accurate effects processing. It should be carefully examined by prospective Quadraverb purchasers as a viable alternative. Had the MIDI control been more versatile it could have had the edge - as it is, there is little to choose between them.

The Digitech DSP-128 Plus
Supplier: John Hornby Skewes & Co Ltd, (Contact Details)
Price: £439

Previous Article in this issue

Altima One

Micro Music - Copyright: Argus Specialist Publications


Micro Music - Jan 1990

Donated & scanned by: Mike Gorman

Gear in this article:

Studio FX > Digitech > DSP 128

Gear Tags:

Digital FX

Review by Jez Ford

Previous article in this issue:

> Altima One

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