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Peavey SDR 20/20 Digital Multi Effects Unit

A refreshingly logical and capable multi-effects unit that successfully combines flexibility with fidelity.

With so many high-spec, digital multi-effects units to choose from, all offering real-time MIDI performance control, what makes the Peavey SDR 20/20 stand out from the competition? Dave Lockwood finds out.

On the technical front, Peavey's SDR 20/20 comes with impeccable digital credentials: 64x oversampled, 16-bit analogue/digital conversion, 18-bit digital/analogue conversion, with 24-bit effect processing in between, the ability to combine effects in any order, and independent memorised level and mix for each preset — yet the 20/20 is simpler to use than many multi-effects units. But does it have the essential, unique selling point?

The key commodity in the multi-effects market now has to be individuality, and I feel the SDR 20/20 sounds just a little bit different, with a quality and character that I find very appealing. On the surface there would appear to be the odd conceptual anomaly; why include guitar distortion and speaker simulator processes in a device that can't actually operate down at passive instrument level? If it is not intended for use as an instrument pre-amp, why are so many of the presets dedicated to specific instrumental usage? Those reservations aside, there are some excellent-sounding processes on the 20/20 — a delicious reverb, some particularly characterful modulation and thickening effects, good clean delays, and quite a decent pitch-shifter.


Ring for a brochure!

If you'd like further information about Peavey's SDR 20/20, or products in the rest of the Peavey range, you can call Carol Wheeler on (Contact Details), or fax on (Contact Details), or write to the address at the end of the review.

The standard 1U rack format is used for the casing, with an integral power supply, fixed mains lead, and a front-panel mounted power on/off switch. Connections, made to the rear only, are electronically balanced quarter-inch jacks, with a pair for both the stereo output and input. Many of the 20/20's processes are in fact true stereo, but for those that are not (Distortion, Overdrive, Reverb, and Stereo Simulator), the dry feed is passed in stereo, with the effect being derived from a sum of the left and right input. The left input alone can be used for a single mono source, and there are MIDI In and combined Out/Thru sockets.

It is most unusual not to find an input level control to play with, but in the 20/20 literally everything is accessed via the software, even the global -10dBu or +4dBu operating level. Overall input and output levels can be trimmed in half-dB steps to 12dB above or below the nominal operating level, and there is a Volume parameter unique to each program. A pair of 5-segment LED column meters are provided, though the 20/20 actually clips rather unforgivingly, so I would be inclined to treat the segment below maximum as peak operating level.

Chains, Banks And Presets

A chain of effects, with its associated user-adjustable parameters and MIDI control assignments, is referred to as a Preset, and it is possible to store the same Preset with different volume settings for live performance. There are 128 factory presets and 128 user presets, with 256 Program locations, designated as Banks A and B. As shipped, the user presets are copies of the factory presets.

The user interface is via data Increment/Decrement switches or a rotary data-entry knob, though MIDI Program numbers allow full random access. The unit also recognises MIDI Bank Select commands, but there is no way to change banks from the front panel without scrolling through the rest of the bank you are in. As you can store any Preset to any Program location, you have, in effect, a complete MIDI Program Change mapping facility.

The display is a two-line, 20-character, backlit LCD and is well organised, initially showing (in Play mode) Program number, Volume setting, and the Preset name and number from which it is derived. The data Inc/Dec buttons actually form the Up and Down elements of a four-way cursor controller which is used to navigate around the display. Assigning a preset to a Program is a simple task, and you can also alter the volume setting at this stage if you need to. Assignments are automatically stored as you make them.

Easy Editing

Hitting the Edit key takes you initially into the Chain Edit display, where you see a listing of all the effects that make up the preset, their order, and whether they are configured in series or parallel. The Chain Edit display allows you to change any of the effects, or their series/parallel connection, then use the data Inc/Dec switches to select from the available pool. The rotary data entry knob remains permanently assigned to the Level value in Chain Edit, enabling effects combinations that are placed in parallel to be balanced relative to one another.

Adding or removing effects from a Chain is also performed in the Chain Edit display, under the control of a dedicated Add/Del button. The default effect is probably not going to be the one you want, so you simply use the data entry switches to scroll through until you find what you are after.

Editing Effects

Placing the cursor under any of the effect names in Chain Edit brings up an abbreviated listing of all the effect's parameters along the bottom row of the display, and a fuller listing of the active parameter and its value on the top row. In this display, the data switches and rotary controller are fully interactive, while an excellent Compare function allows you to refer not just to the unedited version of the preset you started with, but to any of the stored presets. The SDR 20/20 has a consistent, almost intuitive interface, and most users could probably even 'busk it' to this level of operation, straight out of the box.

Naturally you can name your edited preset, and select any of the 128 User locations to store into; there is no global or local memory protection available on the 20/20, so you have to organise your data to avoid accidents.


Unlike some units, there are no inaccessible functions on the minor effects with fixed, 'average' values. Parameters are, however, often expressed in arbitrary units rather than in recognisable units of time, level and so on. For example, the compressor Sustain parameter is expressed simply as a value from 0 to 6. The remaining compressor parameters are Output Level (0 to 100%) and a simple Noise Gate setting with an arbitrary 1 to 10 range. Despite the omission of a Ratio parameter, this proved to be a surprisingly versatile little compressor, being able to perform both as a fierce 'guitar sustainer', and as a more subtle peak controller, useful for allowing a more constant drive level to be maintained for processes later in the chain.

There are two subtly different distortion effects, designated Distortion and Overdrive. Distortion includes a three-band EQ with fully parametric mid section plus Drive and Post Gain parameters. The EQ parameters are expressed as Fat (-50/+50) to control low-frequency gain, plus Body and Edge (-50/+50) for the same at mid and high frequencies respectively. The MF centre frequency may be set from 300 to 900Hz with Resonance offering a 'Q' of anything from 0.1 to 4.9. You can certainly do a lot with this EQ, but it would have been better if the mid extended up another octave. As digital distortion goes, this is on a par with the best I have heard, but it falls short of the better analogue 'amp simulations'.

The Overdrive effect seems, to my ears, to have a similar tonality to the Distortion process, merely at lower gain and sensitivity. Parameters are Low Rolloff (pre-filtering in 100Hz steps from 100Hz to 1,9kHz) and Pre-drive (additional gain from 1 to 10) and Clip (0 to 99). The latter is a further 'soft-clipping' distortion stage, offering additional sustain and a bit more harmonic content. The individual stage Level control can be used to make up gain lost through the limiting action of the clipping circuit.

An essential companion to the distortion effect when it is used for DI recording is the Speaker Simulator. This replicates the response curve of four different types of instrument loudspeaker/cabinet combinations. To my ears, all the variants have either a little too much 'fizz' or too much boom (except for one, which has both), but they are quite usable. On offer is a choice of a single 12-inch (a Peavey Scorpion, allegedly), in either a closed or open-back cabinet, plus two versions of a 4x12 setup. One of these is identified as 'British', by which I suppose they mean Marshall, and is fairly brittle. The other sounds as if it has been miked up from behind. A good speaker simulator will not only smooth out heavily-distorted guitar sounds, it will also be able to add a highly desirable warmth and character to clean ones — a task that the Peavey simulator process does not handle quite so well.

"The reverbs and the modulation group are particular assets, and there are some quite stunning effects to be achieved from this unit by combining the two."

Modulation Effects

The Chorus effect block is actually sufficiently versatile to cover all the effects of the 'short-modulated-delay' group, including Flanging and Vibrato. Sweep rate may be set from 0 to 9.9Hz, which should cover just about every practical requirement. Feedback offers a range from +99 to -99, with the negative figures denoting anti-phase feedback; I have never been able to quite work out the reason, but some sources sound better with inverted flanging and others just don't.

The sound seems to 'move' quite well, giving the impression that the modulation is in opposite phase on the two sides and offering a true stereo operation. In this mode, the channel integrity of a stereo source is maintained. Auto-Pan is available as a separate effect, with Depth (0 to 100%) and Rate (0 to 9.9Hz) settings offering further artificial 'stereo' animation.


The Pitch Transposer is the only process that can be entered into a chain more than once, so although the transposer is mono, stereo shifting can be generated by placing the Pitch 1 and Pitch 2 blocks in parallel, and panning them apart. Maximum shift is one octave in either direction, with the fine-tune parameter in individual cent steps (+/-50), allowing high-resolution control over detuning effects. Budget pitch shifters invariably exhibit unwanted side effects — some units 'warble' disgustingly, whilst others are content to just let you hear a bit of splicing noise. The SDR 20/20's sort of sits in between and, subjectively, it is a pretty good sounding pitch shifter.

Serious Delays

Delay comes in a choice of three varieties: Stereo, Mono, or Tapped. Stereo offers a maximum delay time of 361 mS in each channel, with independent control of feedback. If you're working with a sequencer, delay time may also be automatically matched to tempo by feeding the SDR 20/20 with MIDI clocks, and this proved sufficiently precise for most applications.

Apart from Mix, which sets the direct/effect balance, the only other parameter is Tape Simulator — a low-pass filter prior to the feedback stage, rolling-off at 1kHz, 2kHz, 4kHz, 8kHz, plus an Off setting. If Peavey had been able to build the wow and flutter or tape saturation characteristics of a real tape echo into a digital unit, then they could justifiably call it a Tape Simulator parameter, but as far as I can see, this is just a Low Pass Filter.

The Mono delay allows up to 724ms while the Tapped effect (mono in, stereo out) offers 724mS in each channel, with the tap cluster spaced according to the maximum setting. Feedback is derived from the longest delay available, and roll-off is available to soften the effect. There is no control over tap spacing or individual tap levels, which is a bit limited in comparison with the sophisticated multi-tap facilities offered by some competing units.


There are two main types of reverb on the SDR 20/20 — the basic reverb block used in the multi-effect chains, and the rather more sophisticated 'Ultra-Reverb', which is only available as an individual process. The basic reverb block offers eight types: Plate, Tunnel, Spring, Room, Stage, Hall, Gated and Reverse. Each of these has a fundamentally different character, in keeping with its name — the Plate is bright, with a fast build, the Tunnel is hollow and resonant, the Spring slightly trashy with a flutter. They all work rather well, with the 'natural' reverberation simulations, Stage, Hall and Room being particularly good for a multi-effects device.

The fundamental editing parameter is Size, with a choice of Small, Medium, Large, and Huge! Pre-delay is incorporated within the reverb algorithm, with a range of 0 to 46mS, though I would have liked to see more pre-delay available. Decay Time is fully variable up to 30 seconds, operating in conjunction with the Damping parameter to determine the relative decays at high and low frequencies. Damping may be set to 125Hz, 500Hz, 1kHz, 2kHz, 4kHz, 8kHz, or Off, with the lower settings recommended for 'natural' sounding effects, for HF reverberation decays very quickly in the real-world. Modern production is certainly not always about simulating reality, however, and it is nice to have the option of over-bright reverb for special effects.

Although Ultra-Reverb can only be deployed as a single effect, it actually includes three elements itself — Pre-delay, 5-band EQ (described in the EQ section), followed by the Reverb process. Pre-delay in the Ultra-Reverb block is no longer limited to 46mS, but is a fully-fledged delay stage, extending to 741 mS, with Feedback and Low Pass Filter parameters. The Reverb parameters actually remain the same as for the basic reverb, with the difference presumably lying in the sophistication of the algorithm allowed by the additional processing power available when the unit is virtually dedicated to this one process. If reverb quality and 'character' are an important consideration in your assessment of a multi-effects device, then make sure you listen to the SDR 20/20 before buying anything else, because this aspect of the machine is particularly impressive.

Twice As Exciting

There are two types of Exciter available: one is a digital filter process, used to emphasise harmonic content, presumably by the manipulation of phase, and the other utilising the now familiar controlled distortion process to generate new overtones, harmonically related to the original signal. The digital filter also allows harmonics to be de-emphasised by dialling up a negative Phase setting (range -100 to +100) while the operating frequency is expressed merely as a value between 1 and 10.

The other type of exciter does give you a display of its unusually wide range of operating frequencies, in the form of the Tune parameter, covering 100Hz to 4.9kHz. The Drive control, familiar to users of dedicated harmonic enhancer units, is retained, and there is also a choice of harmonic types — setting 1 adding the smoother, more musical even-order harmonics, setting 2 the harder, brighter, more dissonant odd harmonics, and setting 3 giving both together. This is actually very effective, although it is a bit annoying to have to keep stepping between the Drive and Balance (output mix) parameters while setting up.


You certainly get plenty of choice when it comes to EQ on the 20/20. Apart from those built into other effects, there are no fewer than four different types, offering distinctly different subjective characteristics and levels of sophistication. The Classic EQ is an interactive three-band arrangement, with a sweep-mid, typical of that found in guitar amps. Again, the mid tuning is expressed in arbitrary units (0 to 100). Gain is also calibrated from 0 to 100.

There is also a second, more conventional 3-band EQ, with the sweep mid frequency this time specifically expressed, ranging from 99Hz to 3.3kHz. Actual top and bottom frequencies are again not revealed, but the bands each offer +/-12dB of range, shown rather perversely as +50/-50.

"If reverb quality and 'character' are an important consideration in your assessment of a multi-effects device, then make sure you listen to the SDR 20/20 before buying anything else, because this aspect of the machine is particularly impressive."

Perhaps surprisingly, this EQ does not have a bandwidth parameter, but there is a choice of 'Type' to determine the overall characteristic of the action, with Guitar, Voice and the gloriously named 'Drastic', on offer. Odd though such designations may seem, they do in fact give you a good idea of what to expect from this effective and subjectively pleasing EQ.

The comprehensive 4-band parametric is a stereo equaliser with four independent bands, each with the full complement of frequency, bandwidth and gain controls. Each band may be set to operate anywhere between 20Hz and 16kHz, allowing overlapping bands and complex interactions, such as a sharp notch within a broad-band boost. Bandwidth may be varied from one octave down to the ultimate selectivity of one hundredth of an octave. Gain within the band may range from +12dB to -24dB, the difference in the boost and cut figures reflecting the fact that a high degree of narrow-band attenuation can still produce an audibly acceptable result, whereas 24dB of narrow-band boost would be pretty unpleasant.

Finally, there is a 5-band 'Graphic'; a stereo EQ with +/-12dB in each band, located at roughly 'octave-and-a-half' intervals (100Hz, 330Hz, 1kHz, 3kHz, 10kHz). Of course there is nothing actually 'graphic' about it at all, it merely conforms to the general graphic EQ setup of fixed centres and several bands. In use, these are actually effective and versatile EQs, suitable not just for tweaking the tonality of an effects chain, but for more demanding applications like overall program equalisation.


Despite its inclusion in the compressor block, there is also a separate downward expander stage designated as a Noise Gate. Attack and Release are once again set in arbitrary units, although Threshold has a value in dB below digital clipping (-2dB to -90dB). There is a further parameter, Sensitivity, to determine the fully closed setting. A dedicated Hum Filter is also offered, with just a single parameter, selecting 50 or 60Hz operation, covering both European and USA mains frequencies. This utilises narrow-band notch filters and is very effective in reducing hum without spoiling the sound being treated.

The remaining effects are a simple two-channel mixer, with just Level and Pan, and a Stereo Simulator. The latter uses the usual comb-filter approach, added on one side and subtracted on the other, to create complementary narrow-band frequency differences which can sometimes deceive the ear into hearing a degree of 'spread' on a previously mono source. A few sensible parameters are provided, namely Tune to set the distance between frequency bands, from 100 to 500Hz, and Effect Depth. A fixed characteristic Low Pass Filter can be switched in to bypass the comb filtering at low frequencies, which helps keep the bass centred in the synthesised image.


The SDR 20/20 is undeniably a very high quality audio processor. It is conspicuously clean and quiet, when correctly interfaced, with a transparent, wide-bandwidth signal path, and decent data exchange and external control facilities via MIDI. Perhaps the vital quality that will set it apart is the sheer 'strength' of some its effects and combination presets. This, of course, is highly subjective; what works for me may well not work for you, but these are effects that found myself wanting to hear plenty of in the mix, rather than attempting to bury them.

The reverbs and the modulation group are particular assets, and there are some quite stunning effects to be achieved from this unit by combining the two. suppose I must also include the EQs in the commendation list for these are digital EQs that genuinely sound good, and with so many to choose from, you can always find just the right one for the job.

I have reservations about the guitar-orientated distortion and overdrive effects. There is a bit too much of a 'threshold effect' about the distortion to allow the player to exploit a sensitive right-hand touch. High levels of compression exacerbate this problem, for me, and whilst it does help notes 'hang on' for a long time, it also leaves a lot of work for the expander to do as source noise is pumped up. The flat-out, 'everything-on-11' rock sounds have plenty of power and bite, with harmonics spontaneously leaping off the pick. The 'glassy' clean DI tones are fine too, it is perhaps just some of the subtle shades in between that miss out a little.


  • Good user interface.
  • Excellent reverbs, modulation effects and digital EQ.
  • No restriction on effect assignment.
  • High quality audio signal path.
  • Flexible and effective MIDI control.
  • Realistic price.

  • No instrument level input.
  • Guitar effects not always convincing.
  • Lack of basic footswitch options.


Assessing the total package, of course one can find things to criticise — it is too easy to run out of internal headroom through basic parameter gain settings; the switches are a bit poor on tactile feedback, leaving you sometimes unsure whether a press has registered or not; the lack of visible response to MIDI and lack of a hardware bypass footswitch are regrettable omissions. None of these can be regarded as a damaging operational drawback when set against the positive points, however, leaving the SDR 20/20 looking like a very strong contender in the digital studio effects market. As I said at the beginning of this review, with so many good all-rounders available already, a degree of individuality has to be the key ingredient for the newcomers. Fortunately for Peavey, I think the SDR 20/20 has enough.

Further Information
Peavey SDR 20/20 £649 including VAT.

(Contact Details).


Frequency response (+1/-2dB) 12Hz to 20kHz
Distortion (1VRMS @ 1 kHz) 0.01 %THD
Signal to noise ratio >90dB
Maximum input level (+4dBu) 20.2dBu
(-10dBu) 12.4dBu
Maximum output level (600 Ohms) (+4dBu) 18.5dBu
(-10dBu) 11.0dBu
Input impedance 68kOhms (stereo), 34kOhms (mono)
A/D conversion 44.1kHz, 16-bit, 64x oversampled
D/A conversion 44.1kHz, 18-bit
Presets/Programs 128 factory presets
128 user presets
Mappable to 256 Programs
Maximum simultaneous effects 8
MIDI controllers per Preset 8

Also featuring gear in this article

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Recording Musician

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Stereo Mic Techniques

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 - Dec 1992

Gear in this article:

Studio FX > Peavey > SDR 20/20

Gear Tags:

Digital FX

Review by Dave Lockwood

Previous article in this issue:

> Recording Musician

Next article in this issue:

> Stereo Mic Techniques

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