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Peavey SDR 20/20

Digital Multi-Effects Unit

A seductive combination of versatility, high sound quality and ease of use, all in an affordable, 1U rack package — Paul White looks at Peavey's new SDR20/20.

Peavey's SDR 20/20 is a multi-effects unit offering most of the familiar effects as well an impressive digital EQ section capable of emulating a traditional 5-band graphic EQ, a 4-band, fully parametric EQ, a simple 3-band EQ with a sweep mid, and guitar equalisation. Some of the effects function in true stereo whereas others, such as Distortion, Overdrive, Reverb, and Stereo Simulator, maintain the stereo integrity of the dry signal but generate a stereo effect based on the sum of the left and right inputs. Up to eight effects may be combined at one time with no restrictions imposed by the used of preset effect algorithms.

The technical spec reads almost like that of a current CD player, but the same can be said of many of the latest breed of digital effects processors. The unit employs 64x oversampled 16-bit analogue-to-digital conversion, 18-bit digital-to-analogue conversion, and 24-bit internal processing.

The SDR20/20 permits extensive effect editing and appears to have fewer restrictions than many competing units. But when it comes to the way in which the various effect blocks can be combined, the operating system is reassuringly logical, almost to the point of being intuitive. Indeed, the whole unit has a kind of assured, understated appearance with very few controls.

The 1U front panel is graced with a single LCD display window, eight access buttons, four cursor buttons and a data entry knob. Other than the mains switch, that's your lot. The rear panel is similarly sparse with unbalanced jack inputs for Left/Right in and Left/Right Out, plus MIDI In and MIDI Out/Thru DIN sockets. Mains is fed directly to the unit — there's no external adaptor.

The unit's inputs and outputs can be set up in software (via the Utility page) to conform to either -10dBv or +4dBu operating levels and, unusually, the input and output gain controls are also accessed via software rather than by the more familiar rotary controls. The input and output levels can be tweaked in half dB steps over a range of 12dB above or below the nominal operating level. Metering is via a couple of 5-segment LED column meters, the top section being labelled as 0 VU, though as the unit clips rather abruptly it is best to keep the signal below this level. However, there is no instrument level input; given that the unit includes guitar overdrive, speaker simulation, specialised guitar EQ and suchlike, I really can't understand the logic behind this. If you want to plug a guitar into the unit, you'll need to go via an active DI box or specialised guitar preamp.

One valuable feature, omitted on many competing units but not on the SDR 20/20, is the ability to program a different level setting for each effects program. A chain of effects, its parameter settings and its MIDI control assignments, is termed a Preset, and because each program can have its own level setting, it is possible to used the same Preset at different levels in different programs.

There are two sets of 128 Presets available in the SDR 20/20: 128 factory settings which can't be altered, and 128 user locations which, as shipped, contain duplicates of the factory patches. There are also two banks of programs, A and B, which act rather like an assignment table in that any preset can be assigned to any program in either bank — as shipped, however, the factory presets are addressed from bank A and the user presets from bank B. As with most such units, there is an additional edit buffer which allows the user to make changes to a sound without overwriting the original. You can save the edited sound to a new location, to the same location, or just give it up as a bad job.


The user interface combines the familiar cursor buttons with a rotary, data entry controller, while MIDI Program changes can be used to call up effects directly. The unit recognizes MIDI Bank Select commands, so any of the 256 programs can be accessed over MIDI with no problem, but it's a little slower to gain access from the front panel. There is no bank switch on the front panel, so to get from one bank to another you have to scroll through all the programs in between — tedious. However, as you can store any Preset to any Program location, you can store all your favourite effects programs close to each other.

The backlit LCD is 20 characters wide and can show two lines of text or data. In Play mode — the normal operating mode of the machine — the Program number, Volume setting, and the Preset name and number from which it is derived.

The first step when editing is to get into the Chain Edit display by hitting the Edit key. Here you select the effects that make up the preset, their order, and their series/parallel status. The rotary data entry knob controls the Level value in Chain Edit so that the levels of the various effects can easily be balanced.

Effects are added or removed from the chain using the Add/Del button, and if the default effect isn't what you want the data entry switches let you scroll through and select from the available effects.

Individual effect parameters can easily be edited, and during this operation the data switches and rotary controller are fully interactive. The Compare function enables the currently edited patch to be compared with any of the stored Presets, which is a nice touch.

Once edited, Presets can be named and then stored into any one of the 128 user preset locations. Be warned though — there is no way to lock your programs, so take care not to overwrite anything you especially want to keep.

All the essential effect parameters are accessible to the user, though it is frustrating that the values are presented on arbitrary scales, eg. 1 to 10, rather than in the appropriate units. This is especially frustrating when working with delay or reverb decay times.


Many digital compressors are rather disappointing, but the one included here is actually rather good. This includes a simple Noise Gate to mop up low level noise during pauses, though the compressor itself has no Ratio parameter. Even so, the unit proved useful as a guitar sustainer and as a safety limiter to prevent overload further along the chain of effects in a program.

When it comes to guitar sounds, there's a choice of Distortion and Overdrive. Distortion has a Drive parameter to set the actual amount of distortion and Post Gain control to set the output level. Tonal control is possible using the 3-band guitar with parametric mid. The EQ is very flexible, though the sweep mid could use a wider range, and while the actual guitar sound isn't at all bad it still isn't as convincing as a good analogue preamp and certainly less effective than a valve preamp.

Overdrive is similar but less distorted and with a simpler filtering arrangment. It also has a further 'soft-clipping' distortion stage which can sound nice.

The guitar overdrive effects work well enough when amplified via a guitar combo, but plugged directly into a mixing desk, they need to be used before the Speaker Simulator effect or they sound, predictably, thin and edgy. Again, I've heard better results from a dedicated, analogue speaker simulator, but this one is quite versatile and offers four quite different settings designed to emulate stacks, combos and the like. It manages to thicken the overdrive sound while removing most of the buzzy edge, but clean sounds don't work so well — you don't quite get that warm but bright jangle that comes from a really good guitar combo.

One area of the SDR20/20 that is guaranteed not to disappoint is the chorus section, which also handles other modulated delay effects such as Flanging and Vibrato. There's plenty of range in terms of depth, rate and feedback with a phase invert function offering a subtley different kind of coloration on flanging effects.

The modulation sweep is in different directions on the left and right channels which creates a good impression of movement and holds together quite well if the effects is summed to mono.

Chorus effects can also be created using the pitch transposer to create subtle detuning effects. This is only a mono effect, but it can be assigned twice in a block enabling a different degrees of shift to be set up and panned to different sides of the stereo image. Fine tuning is in one cent steps with a maximum coarse shift of one octave in either direction. Though the inevitable side-effects of pitch shifting are audible on anything other than subtle shifts, these are less serious than on many budget units and the shifted sound is musically useful if mixed with a healthy dose of the unshifted sound or treated to a heavy dose of additional effects.

There are three types of unmodulated delay available; Stereo, Mono, or Tapped. In stereo mode the maximum delay time is limited to 361ms per side, though the amount of feedback may be set independently. There's also a low-pass filter which takes the edge off successive echoes with a view to approximating the sound of a tape echo unit. A nice alternative to setting the delay manually is the ability to use MIDI clock information to automatically set a delay time related to musical tempo. The available delay time is doubled (724ms) when Mono Delay is selected.

The Tapped Delay mode works in stereo with a maximum delay time of 724ms, but there is no way to adjust the individual tap spacing.

Although there are virtually no limitations as to how the internal effects may be configured, Peavey have provided the option to blow all your processing power on one really good reverb effect, called Ultra Reverb. In normal effects mode, the reverb is still very good, but Ultra reverb is so complex it uses all the processing power of the machine.

The basic reverb types are; Plate, Tunnel, Spring, Room, Stage, Hall, Gated and Reverse. These all have the kind of character you'd expect: the plates are fast and bright, the halls slower and warmer, and the spring is obviously fluttery. User variable parameters are: Size, (Small, Medium, Large, and Huge), Pre-delay (0 to 46mS), Decay Time, (30 seconds max), and HF Damping with a range of operating frequencies from 125Hz to 8kHz. Damping may be turned off to create artificially bright effects.

When Ultra Reverb is selected, you can also apply a 5-band equaliser to add further tonal variety to the reverb sound while the pre-delay time can be increased right up to the 741ms used in the mono delay effect, complete with Feedback and Low Pass Filter. Otherwise, the parameter options are identical, the difference being in the density and subjective quality of the reverb produced. And I have to say that Ultra Reverb is very good indeed.

Interestingly, a basic Pan effect is included, and though this is a simple free-running autopan with variable depth and rate, it works in true stereo with a stereo input and can be used in combination with the other effects to create an interesting sense of movement. This is especially effective when the pan rate is close to the track tempo — in that context, a MIDI triggered pan option would have been welcome.


Amongst the more conventional effects are not one but two different Exciter treatments. Though the operating principles are not quite clear, the first appears to be a dynamic equaliser or filter which can be used both to emphasise and de-emphasise high frequency detail while the second uses the more familiar system of harmonic generation. The harmonic enhancer has control parameters corresponding to those on dedicated analogue units such as Tune (100Hz to 4.9kHz), Drive and Balance. There is also a choice of even-order or odd harmonics, or both. In practice, the Exciters work quite well, but are not as easy to set up as the analogue type where you can adjust two parameters at a time if need be.


When it comes to EQ effects, there are four different types designed for instrument, guitar and general use plus a separate section dedicated to creating swept filter or auto Wah Wah effects. The Classic EQ is a 3-band configuration design to emulate the passive EQs in classic guitar amps, This has a a sweep-mid control though, annoyingly, this is again calibrated in meaningless units rather than in actual frequency.

Next along is the 5-band stereo 'Graphic' EQ giving up to 12dB cut or boost at 100Hz, 330Hz, 1kHz, 3kHz, 10kHz. This is quite straightforward though not, of course, as easy to set up as one with real sliders.

Moving along again, we come across the 3-band EQ, with the sweepable mid, the latter covering the range 99Hz to 3.3kHz. The sweep is not fully parametric and so doesn't have a bandwidth or Q parameter, but there are three preset 'Type' variations charmingly tagged Guitar, Voice and Drastic.

Far more powerful, in many respects, is the 4-band parametric stereo equalizer, each band having its own frequency, bandwidth and gain settings. All the bands are tunable over the range 20Hz and 16kHz which is flexible enough let you overlap bands or notch out narrow regions within a wider band of boost. The range of bandwidth adjustment is extraordinarily wide extending from one octave down to just one hundredth of an octave. Up to 12dB of boost or 24dB of cut may be applied in each band.

Also based around sharp notch filters is the dedicated Hum Filter which can be set for 50 or 60Hz operation only. The information doesn't say whether this notches out just the fundamental hum frequency or whether it also tackles some of the harmonics, but is certainly helps clean up guitar tracks where the single-coil pickups have been picking up hum from transformers and lighting circuits. Other than the choice of mains frequency, there are no user parameters.


The Noise Gate is actually based around a downward expander with variable attack and release parameters. The operating threshold may be set anywhere between -2dB and -90dB relative to an input signal at 0VU. Because this is an expander and not a gate, a further a Sensitivity parameter has been added which specifies how far below the threshold the input signal must fall before it is fully attenuated. This the manual doesn't say as much, this appears to fill the same role as expansion ratio.

Also on the menu is a basic 2-channel mixer, with Level and Pan controls. I can't see many users needing this on its own as a mixer, but it can be useful in positioning the dry left and right input signal in the stereo soundfield, especially where the inputs are discrete mono sources and not true stereo.

A Stereo Simulator is included in the effects department, and this uses a delay-based comb filter to provide a modified frequency response one one side and its compliment on the other. In theory, when the two sides are summed to mono, you should end up back where you started. Tune sets the spacing between the frequency bands of the comb, (100 to 500Hz), while Depth sets the depth of the notching and hence the magnitude of the effect. A Low Pass Filter can be switched so that bass sounds are unaffected.


Up to eight MIDI control assignments can be stored as part of a preset allowing real-time MIDI control over selected effects parameters. The range of control sources is: controllers 1 to 120, Aftertouch, Pitch Wheel, and MIDI Note-on number. There is also real-time MIDI control — scaling which modifies the degree to which incoming controller values affect the chosen parameters. This includes the ability to invert the control function. However, there's no display of the parameter changes taking place under MIDI control, which is a little disappointing. In practice, the SDR 20/20 responds quite smoothly to external MIDI control with no apparent roughness or glitching.

SysEx handling allows dumping either to a sequencer/data disk or another SDR 20/20 and dumps can comprise the entire user memory, individual presets, or banks of 10 consecutive presets. The performing musician working with the SDR 20/20 would do well to consider some form of MIDI control system as there's no other option for remote control via conventional footswitches. You can't even bypass the effects by foot without MIDI! In the studio, this is less of a problem.


The SDR 20/20 has the advantage of a logical operating hierarchy, a great deal of flexibility and some great sounding effects. Technically, the unit is clean enough and quiet enough for very serious professional use, though you do have to keep an eye on the input levels as distortion is both immediate and drastic once the machine is overdriven. I really don't know why the manufacturers don't provide us with the option of an analogue safety limiter at the front end to avoid this risk.

The reverbs and the modulated delays are perhaps the strongest areas of the machine and when used in combination, some very powerful composite effects can be achieved. In particular, the chorus and flange settings are excellent and this unit comes far closer than most to emulating real tape phasing. Also impressive is the quality and versatility of the equalizers, as these are so often disappointing on budget effects units.

As a guitar player, I find the lack of a guitar input an astonishing omission, and though you can get into the unit via a DI box or the send/return loop of a guitar amp or preamp, I feel this really restricts its applications. The guitar sounds themselves work well in some instances but fail in others. Crystal clean sounds are no problem, and the same is true of the out-and-out mayhem settings. But like the vast majority of these devices, take away the veneer of effects and you're hard put to get a guitar sound that you really believe came from an amplifier. This is especially true of those subtly overdriven blues tones.

The pitch shifter doesn't stand up to close a scrutiny, but it is much more useful than on many multi effects units. And after all, the SDR 20/20 still costs less than the VAT on a serious, dedicated studio pitch shifter.

Areas I'm not too enthusiastic about are the software in and out level controls, the lack of a more direct method of front panel patch access, and the lack of even a basic bypass socket. I know MIDI foot controllers only cost a couple of hundred pounds or so, and I know they really do make life easier, but you'd be surprised how many people don't have them and seem to have no intention of buying them.

Despite these criticisms (the seriousness of which will vary according to your application), this is a sensibly priced and user-friendly effects unit which produces the most commonly used studio effects to a very high standard, with the minimum of background noise. The effects all have a unique character, especially the luscious modulation and reverb effects, while the Ultra Reverb setting stands up well against dedicated reverb processors. Ironically, the very friendliness of this unit might be its own worst enemy when it comes to shop sales — it's hard to believe that such a straightforward box with so few buttons gives the user access to such as staggering range of really great effects.

Further information

Peavey SDR 20/20 Digital Studio Effects £649 inc VAT.

Peavey Electronics UK Ltd, (Contact Details).


Chorus (inc. Flange, phasing Vibrato)
Auto Pan
Exciter 1
Envelope Filter
Classic EQ
5-Band Graphic EQ
3-Band EQ with Sweep Mid
4-Band Parametric EQ
Hum Filter
Noise Gate
Pitch 1 & 2
Speaker Simulator
2-Channel Mixer
Stereo Simulator


FOR: Intuitive user interface, excellent reverbs and modulation effects, flexible and effective EQ, no restriction on effect assignment, high quality audio signal path, flexible and effective MIDI control, realistic price.

AGAINST: No instrument level input, guitar effects not always convincing, lack of basic footswitch options.

SUMMARY: A very high quality, easy to use multi-effects processor but with a few unexpected omissions.


Frequency response (+1/-2dB): 12Hz to 20kHz
Distortion (1VRMS @1kHz): 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-to-D conversion: 44.1kHz, 16-bit, 64x oversampled
D-to-A conversion: 44.1kHz, 18-bit
Presets/Programs: 128 factory presets
128 user presets
(All mappable to 256 Programs)
Maximum simultaneous effects: 8 (in any order)
MIDI controllers per Preset: 8

Also featuring gear in this article

Previous Article in this issue

What's The Big Idea?

Next article in this issue

Drum Programming

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


Sound On Sound - Apr 1993

Donated by: Russ Deval

Gear in this article:

Studio FX > Peavey > SDR 20/20

Gear Tags:

Digital FX

Review by Paul White

Previous article in this issue:

> What's The Big Idea?

Next article in this issue:

> Drum Programming

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