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Parallel Lines

Ensoniq DP/4 Effects Processor

Four into one will go, as Derek Johnson discovers when working with Ensoniq's new four-channel parallel effects processor.

Four high-quality digital processors in one supremely versatile, multi-effects package. Derek Johnson puts it to the test.

Ensoniq are well known for their samplers and synths, many of which have high-quality, on board digital effects, so a move into the digital effects market is quite logical. With the effects market being so crowded, you might be inclined to think we need another effects unit like a fish needs skis, but Ensoniq's DP/4 parallel effects processor turns out to be a little bit special. The product is called a parallel — rather than multi — effects processor because, within the confines of its 2U package, the DP/4 has, in effect, four discrete effects processors — termed 'Units'.

An easy way of looking at the DP/4 would be as a virtual representation of four separate digital processors with integral digital patchbay and mixer. There are four inputs and four outputs in all, with several ways of using these, either separately or in combination, to produce mono or stereo effects. It's possible to chain all four effects internally (with each effects module having the choice of any of the onboard algorithms), or all four may be used as separate processors, with stereo or individual mono outputs. The system uses 16-bit linear conversion with 24-bit internal processing, giving an audio bandwidth extending to 18kHz.

The styling of the DP/4's black front panel is a good mixture of old and new touches. Inevitably, there is a data entry knob, a 32-character liquid crystal display, and so on, but there is also a collection of chunky, chrome covered knobs. They don't actually help with the programming, but allow you to have constant control over the input and output levels going to and from each of the four effects units. There is also a pair of level LEDs above each knob, green for signal and red for peak. There's also a two-digit LED numeric display which shows patch numbers, parameters and so forth.

Under the display are a Write/Copy button, a Cancel/Undo button, left and right arrow buttons (which change parameters, as opposed to values, during editing), and three mode buttons: Select, Edit and System/MIDI. Under the big wheel are the effects Unit buttons, labelled A, B, C and D, plus one labelled Config. The Unit buttons each have a pair of LEDs above them, one (yellow) to indicate that it is available in the current preset and one (red) to indicate that it's bypassed.

Round the back are the connectors: three MIDI sockets, a footswitch and a CV pedal socket, plus eight audio sockets — four in and four out. How these outputs are configured depends on how the individual effects units are configured; I'll get to that soon. Input one is duplicated on the front panel, for use with a guitar. There's no phones socket for guitar practice, though.

There are 400 Presets in the DP/4, 100 for each Preset type; 50 are ROM and 50 are user-definable RAM. As shipped, the DP/4 is filled with factory settings, even the 50 RAM slots. These factory settings can be recalled at any time, and are restored whenever the machine is initialised.


At the heart of the DP/4 is the familiar algorithm, which is simply an effect with a selection of parameters, such as 'Small Room Reverb', 'Speaker Cabinet' or, in a more complex vein, 'EQ-Panner-Delay'. There are 46 algorithms altogether (plus a 'No Effect' option), and they are all supplied with a comprehensive selection of parameters — 14 parameters at least, 31 at most.

"The DP/4 is easy to use and is completely flexible, all the routing taking place internally, in the digital domain."

The next step up is the Preset, which consists of an algorithm or algorithms with various parameters; there are four Preset types, consisting of 1, 2 or 4 Units. I said there were four Preset types, and the last one is the Configuration Preset. A Configuration determines the number of source inputs that are to be processed by the DP/4 and how the inputs, Units and outputs are routed. A Config Preset is the highest level of the DP/4 and comprises a collection of algorithms, signal routing and mixing information.

The DP/4 can handle up to four input sources, although a stereo keyboard would be counted as one source while actually using two of the inputs. This is the kind of thing that is handled by the Configurations section. There are two options given for one, two and three source Configs: mono in or stereo in. The four source Config, on the other hand, offers the option of stereo out or four mono outs.

Note that when you turn on your DP/4 for the first time, only 12 of the most commonly used Config Presets are available. This is a deliberate ploy to minimise confusion in the early stages of using the unit. The remaining 88 presets can be revealed by a function in System/MIDI mode. I suppose that's one way of making you read the manual!

Although the algorithm is the simplest building block, there are a couple of algorithms that use the processing power of more than one Unit to function: PitchShift 2U and 3.3 Sec Delay both use two processing Units, and the Vocoder uses all four. Apart from that there are five 'straight' reverbs, from Small Room to Hall, with a couple of reversed reverbs, a gated effect and three non-linear reverbs. There are four delays: multi-tap, dual, tempo and EQ-DDL with LFO. Those in need of guitar effects will welcome the VCF-Distortion (capable of distortion, wah-wah and auto-wah effects) and three guitar amp effects, two of which feature great tube emulations. There are also some speaker simulations — the tunable speaker is perfect for those AM radio and 'voice-down-the-telephone' effects. The remainder consists of a wide variety of choruses (including an eight-voice chorus), flangers, phasers, pitch shifters, a de-esser, a rumble filter, a ducker/gate, parametric EQ, a Vocoder (all four units), and a sine/noise generator. There are three kinds of expander, an EQ-Compressor and a Van Der Pol Filter, which adds an exciter effect to brighten sounds, and particularly benefits plucked sounds. Some of the single algorithms can be seen as multieffects in their own right. These algorithms consist of Chorus, Vibrato, Panner, Flanger and Tremolo, with EQ before and a delay after.


Configurations are based around the various ways in which the four effects 'Units' can be patched together, and each Unit within a Config can have its own MIDI channel and output.

"The guitar effects certainly have an 'in your face' quality to them — convincing amounts of hum, grunge and feedback emanate from the unit when in hooligan mode."

In Select Mode, the display shows the current Preset's number, name, Unit algorithms, the currently selected Unit and the signal routing. This is shown by the characters between Units: an arrow means a serial signal flow, a plus sign means parallel and a two-way arrow means a feedback loop. No symbol between Units means that the Units are not connected and are behaving as independent processors, and an asterisk means that two or more Units are ganged together, using the processing power of both Units. This last option only turns up on PitchShift 2U algorithm and Vocoder 4U.

To programme this unit, you have to keep a clear mind, but the manual does give a clear, non-technical explanations of what's going on. For example, the Phaser-DDL algorithm has parameters dubbed Phaser LFO Width and Phaser Center. You'll know exactly what to do with them when you read that high values of LFO Width give a very high and very low 'woosh', and that the Phaser Center allows you to adjust where the spectral location of the 'woosh' sound is.


The comprehensive MIDI implementation allows for control of up to eight sources at once, from a choice of over 138. A CV pedal can also be used to control one parameter. Streamlined access to the presets may be achieved through the MIDI Program Change map, a bit long-winded but not difficult. Patches can also be incremented or decremented by a single footswitch or by using Ensoniq's special dual footswitch, which allows you to increment with one pedal and decrement with the other. Each effect can be responsive to MIDI Controller 7 (volume) on its own channel, for 'automated' mix control.

In Use

Used on keyboards, guitar, drums or vocals, the DP/4 sounds great. The only noticeable noise comes about as a result of you overloading the unit or due to the nature of the algorithm. For example, going for a distorted guitar effect will inevitably result in some noise, hiss and distortion, but that's as a result of the high gains required to create the effect.

Trying to describe reverbs is always a difficult task, but I have to say these are very musical. Adjectives that spring to mind are 'silky' and 'organic'. I tried nearly all the reverb algorithms, both singly and in Configs of up to four effects, and they sound very natural, while being surprisingly versatile.

Small Room Reverb Parameters

01 Mix
03 Room Decay
05 Room LF Decay Time
07 Room HF Bandwidth
09 Room Diffusion 2
11 Room Detune Rate
13 Room Primary Send
15 Room Ref 1 Level
17 Room Ref 2 Time
19 Room Ref 2 Send
21 Position Balance (2)
23 Modi Source
25 Modi Param Range Min
27 Mod2 Source
29 Mod2 Param Range Min
02 Volume
04 Room Predelay Time
06 Room HF Damping
08 Room Diffusion 1
10 Room Decay Definition
12 Room Detune Depth
14 Room Ref 1 Time
16 Room Ref 1 Send
18 Room Ref 2 Level
20 Position Balance (1)
22 Position Balance (3)
24 Modi Destination Param
26 Modi Param Range Max
28 Mod2 Destination Param
30 Mod2 Param Range Max

The musicality of the reverbs carries over to the remaining effects, with an overall natural quality and smoothness. Quite often a single effect (such as chorus or phasing) sounded so perfect that no further processing was necessary. The 'Eight Voice Chorus' algorithm was a real treat for acoustic guitar, and it was hard to believe there was no reverb with the effect, the sound was so natural.

Real treatments that were rather good included the 'Bright' and 'Warm Vocal Chains', and nearly all of the distorted guitar effects — some of these make nice use of stereo spread, for a really big sound. I initially had reservations about the amp/distortion sounds, finding them a little artificial. However, they grew on me in a big way, and I was impressed by the illusion of real amp feedback and hum — virtual amplifiers! A four-Unit preset called '32 Voice Chorus' also proved to be rather sexy.


There have been multiple processors before, but few seem to be as well thought out as this one. It's hard to sum up the sound of the DP/4 succinctly, since it can be such a wildly different beast at different times, but it always sounds very classy and musical. The reverbs are smooth and natural, providing a convincing illusion of space. The delay effects are very clean and the pitch-shifts are perfectly usable — even so, they are best left for thickening effects or creative big sounds. With larger pitch shifts, you tend to notice the delay, and though they are a little lumpy, they're better than you get from most mid-priced units.

Though there's no dedicated sampling option, weird sample-type effects can be had with the two-Unit 3.3 second delay — play up to 3.3 seconds of music and it loops as you play over the top of it. It's not anywhere near grungy enough to sound like tape, but otherwise, it's just like playing with a big tape loop, which will be welcomed by Fripp-a-likes everywhere.

Apart from the actual sound of the effects, I welcome the inclusion of a vocoder, appreciated the maximum delay time of nearly six seconds, and boggled at the maximum reverb decay of over four minutes!

Those DP/4 Algorithms In Full

Small Room; Large Room; Hall; Small Plate; Large Plate; Reverse Reverb; Reverse Reverb 2; Gated; Non Lin1 2 and 3.

Delay & Time Domain Effects
Multitap; 3.3 Second (2U); Dual; Tempo; EQ-DDL with LFO; 8 Voice Chorus; Flanger.

Guitar Effects
VCF Distortion; Guitar Amp 1, 2 and 3; Speaker Cabinet; Tunable Speaker; Rotating Speaker.

Compound Effects
EQ-Chorus-DDL; EQ-Vibrato-DDL; EQ-Panner-DDL; EQ-Flanger-DDL; EQ-Tremolo-DDL; Phaser-DDL; EQ-Compressor.

Pitch Shift Effects
Pitch Shifter; Pitch Shift 2U; Fast Pitch Shift; Pitch Shift-DDL.

Expander; Keyed Expander; Inverse Expander; De-esser; Ducker/Gate; Rumble Filter; Parametric EQ; Van Der Pol Filter; Sine/Noise Generator; Vocoder (4U).

Depending on how you use it, the DP/4 could be either a four-way multi-effects processor, for treating one signal in mono or stereo, or four individual effects processors with stereo or mono outputs, and pretty well everything in between. The MIDI implementation goes so far as to allow timed delays to be measured against incoming MIDI clocks, which takes whatever hardship there was out of working out rhythmic delays. There's a delay time choice of ordinary notes, dotted notes and triplets from quarter up to 32nd notes.

Guitarists haven't been left in the cold: the guitar effects certainly have an 'in your face' quality to them — convincing amounts of hum, grunge and feedback emanate from the unit when in hooligan mode. The sample and hold waveform on the Phaser algorithms makes for some rather odd, Zoom-like effects which have applications both for guitar and keyboard use.

Most conventional multi-effects units limit your configuration options and are far less flexible than a system you can patch to your own requirements.The DP/4 offers this kind of flexibility while being able to patch any effect to any other in the digital domain. I think Ensoniq have come up with a very versatile input/output arrangement, but I wonder if it would have been financially prohibitive to provide either eight outputs or four stereo jack sockets so that the truly indulgent could return all four stereo outputs (of which the unit is internally capable) separately. This isn't a significant limitation, and in practice, being able to return four stereo effects via a single stereo pair is definitely the more elegant solution.

Apart from sounding very impressive, the DP/4 is easy to use and is immensely flexible, all the routing taking place internally, in the digital domain. There is a psychological price barrier at £1000 or so for effects units, but for the user wanting to combine real flexibility with professional sound quality, I feel the asking price is very fair. After all, we were paying this much for really basic reverb only units five or six years ago. And after all, Ensoniq are providing four separate, high quality effects processors packed in a box, which works out at well under £300 a processor!

Further Information
Ensoniq DP/4 £1179 including VAT.

Sound Technology plc, (Contact Details).

Also featuring gear in this article

Previous Article in this issue

Instant Hip

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Dolby S Explained

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


Recording Musician - Aug 1992

Donated & scanned by: Mike Gorman

Gear in this article:

Studio FX > Ensoniq > DP/4

Gear Tags:

Digital FX

Review by Derek Johnson

Previous article in this issue:

> Instant Hip

Next article in this issue:

> Dolby S Explained

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