The SDE 1000 is part of a range of high quality digital delay lines from Roland and retails for £399. The unit is housed in a standard 19" rack cabinet and has been squeezed into the popular 1U (44mm high) format.

The system is microprocessor controlled and has the facility to program up to four control group settings and store them in memory for later recall, thus making four favourite effects available as soon as the unit is switched on.

The unit itself is very smart in appearance with a matt black finish. The selected delay time is permanently shown on a 4 digit LED display which is large and very bright. All controls are also colour-coded for simplicity of use. Delays of up to 1125 milliseconds are available and such delay times are perfectly adequate for the vast majority of serious uses to which the unit might be put.

An internal low frequency oscillator (LFO) is included to allow modulation of the clock signal for vibrato, flanging and so on, but this may be replaced by an external signal derived from a footpedal which is available as an option.

Controls

The rear panel holds two controls - a rotary pot which multiplies the delay time from x1 to x1.5, and a gain selector which changes the input sensitivity from -20dBm to -35dBm to allow the system to be used with various pieces of equipment. Quite why +4dBm setting (for use with standard studio equipment) is not provided escapes me somewhat, since it is provided with the SDE 3000 (which is another model in the Roland range).

The input preamp which offers gains between -30dB and 0dB enables the correct signal level to be set without any difficulty. This control has an associated VU meter, consisting of six LEDs, which ranges from -20dB to +6dB. A feedback control provides positive feedback for use in effects such as flanging and echo and can be used to drive the unit to oscillation, since it may be advanced to give a loop gain which is greater than one. An override switch is included which reduces the feedback to zero by breaking the feedback loop whilst a delay output pot can be used to vary the balance between the direct and the delayed signals.

The modulation section has controls to vary the rate of the low frequency oscillator and the depth of the modulation. The oscillator can go fast enough to give vibrato effects although Roland do not actually state its maximum operating frequency. Again an on/off switch is included to disable the modulator.

The delay time may be altered using two momentary action switches - increment and decrement. These controls operate in steps of 1ms for delays greater than 10ms and in steps of 0.1ms for delays less than 10ms. This allows the delay time to be set up very accurately, which helps a great deal as the character of an effect such as flanging is strongly dependent upon the delay used (with shorter delays tending to accentuate the higher frequencies present in the signal). Hence the system is very flexible and allows an effect to be altered very slightly to give subtle changes. If the two switches are held down for more than half a second or so an auto repeat function is obtained. Unfortunately, the auto repeat is slightly slow and long delays can take quite some time to set up. This might be acceptable in a studio environment but would be awkward on stage. The problem can be solved to some extent by programming effects into memory beforehand, more of which later. A delay x2 switch is included which simply doubles the delay time.

A delay phase switch is provided to invert the delayed signal. This can be used in flanging to shift the notches of the comb filter (changing peaks to notches and vice versa) thus adding further variety to the range of effects available. Two LEDs are also provided: one shows whether the effect is active or bypassed; the other flashes at the rate of the LFO to show the modulation speed.

A modulation foot pedal control socket allows an external control voltage (CV) to be used instead of the internal LFO to give manual flange sweeps, for instance. Four additional jacks allow remote switching using footswitches. Delay is a simple bypass switch, causing the signal to pass through the unit unmodified. Hold causes the contents of the memory to recirculate indefinitely. Playmate can be used to quickly program a delay time into the machine since the system stores the time interval between successive presses of the pedal and sets the delay time to that interval. If the interval between the two presses exceeds the maximum permissible delay the unit rejects the attempt and the procedure may be repeated. Finally by using the Preset button you can step sequentially through the channels.

Programming

Programming an effect into memory is very simple. Four independent memory channels are available enabling up to four effects to be stored. Each channel has a corresponding LED which glows when that channel has been selected. The memory stores the delay time and also the state of the four pushbuttons (ie. delay x2, delay phase, modulation on/off, and feedback on/off) but it is still necessary to set the feedback level, the output level, and the modulation controls separately for each sound using the front panel pots.

To store an effect the controls must first be set manually, then the desired channel pushbutton (1 to 4) is held down for about 2 seconds. Once programming is complete the LED for that particular channel will start to flash and the button may be released. The effect is now held in non-volatile memory and will remain there until the channel is reprogrammed, even with the power off.

Electronics

The unit has very good specifications indeed. The x1 range response is 10Hz to 17kHz ( +0.5dB, -3dB) and for the x2 range the figures are 10Hz to 8kHz( +0.5dB, -3dB).

Such high performance is only possible by careful design, and by the use of accurate analogue-to-digital and digital-to-analogue conversion techniques. Unfortunately high resolution converters such as 16-bit devices are prohibitively expensive, whilst 8-bit and 12-bit converters are relatively cheap but far more noisy. A popular solution to this problem it to use a medium resolution chip (perhaps 12 bits) and to employ soft companding, ie. compressing the dynamic range on input and expanding the sound to its original form at the output.

This results in a non-linear quantising system which effectively makes low level signals less likely to become lost amidst a mass of quantising noise (the inevitable noise introduced by any digital encoding process).

When used in this way, the effective resolution of the convertor is increased. If 'hard' companding were used the signal-to-noise ratio would improve even further since the amplitude of the signal would tend to remain almost constant. Unfortunately, this has the effect of transforming any input signal into a series of square pulses and results in strong distortion. Therefore it cannot often be used for signal processing applications. The process of companding has its drawbacks but is beginning to show its worth in systems like the Roland. The unit's 'big brother' (the SDE 3000) claims to employ 'the equivalent' of a 16-bit converter.

Effects

In general the unit produces effects of very high quality and ranks amongst the best of the many systems available at a similar price. The digitised signal comes out cleanly and is free from noise - which is most noticeable when using a good quality amplification system.

Echo effects are very realistic since the repeat is almost indistinguishable from the original. All the usual variations are possible ranging from short, sharp slapback echoes using delay times of 100ms or so, through to full multi-repeat echoes of over one second. If high settings of feedback are used the signal gradually suffers degradation as it is repeatedly coded and decoded. If the feedback control is advanced too far, the feedback loop starts to 'ring' at its natural frequency and oscillation occurs beyond this. The ringing effect is dissonant and could be used to advantage for special effects (with vocals springing immediately to mind). Using long delay settings the output gradually increases towards oscillation and with short delays the output grows very rapidly to a familiar feedback howl. All manner of self-indulgent effects are possible for those so inclined (especially when using long delays) and can be exploited without even connecting an instrument to the unit.

'Doubling' may be achieved using a suggested delay of 30ms with the addition of slow modulation and feedback. This is a commonly used thickening technique which is seldom perceived as a distinct echo, although the repeat is sometimes noticeable on drum tracks.

'Chorus' is an alternative thickening effect and the best chorus generators produce a very rich output. The Roland unit is capable of generating some excellent sounds which cry out to be put on tape. A delay of about 50ms is used with a little modulation (with depth kept low) and a little feedback. With an electric guitar the tonal quality improves immensely on single notes and sounds akin to a 12-string are produced with chords. This was definitely my favourite effect from the unit.

The system works well as a flanger and compares favourably with its competitors. Flanging is sometimes a troublesome effect since the comb filter circuitry expects a signal with a wide harmonic spectrum but does not always receive one. With a guitar the effect is above average and improves with the addition of a tone booster or fuzz box connected between the instrument and the unit to thicken the signal. Using a synthesiser with a nice, rich sound (such as a pulse width modulated (PWM) square wave) the effect improves further.

Vibrato can be easily achieved by adding fast modulation to the clock signal to alternatively speed up and slow down the progress of the digitised signal in memory. Very low settings of modulation depth are necessary to avoid large and unpleasant pitch shifts at the output, but the unit still offers sufficient scope for a sensible effect to be set up easily.

A hard reverb may be coaxed from the unit although Roland do not actually claim the system to be capable of reverberation. As usual with such an effect the results are not particularly natural but are useful in their own right and can improve the ambience of a sound a great deal. A reasonable digital reverberation system is a somewhat expensive prospect and the SDE 1000 offers a good compromise to the majority of buyers for whom cost is a very significant consideration. I suspect the effect will find its uses, if only due to the fine noise figures of the unit.

Conclusions

Despite the apparent worthlessness of the pound these days £400 is still a lot of money and careful thought should be given before parting with the cash. The SDE 1000 can be highly recommended as a flexible, high quality machine which is good value for money. For those with a larger budget Roland also produce similar systems for £600 (the SDE 2000) and £800 (the SDE 3000) which offer slightly higher specifications, improved facilities and longer delay times. The latter unit can produce echoes of up to 4.5 seconds which might be thought by some to be a dispensable luxury. On the other hand the serious user could well consider its better specifications (such as a signal-to-noise ratio for the delayed signal of 88dB) justification enough. The choice is yours.

The unit is well made and, if appearances are anything to go by should give years of good service. All connections are situated on the rear panel to keep wiring safely out of the way, although a front panel input jack would not have gone amiss.

A couple of 2 metre connecting leads are included as accessories. However, footpedals and footswitches are options and will cost you extra. The manual supplied in the package is adequate since the unit is almost self-explanatory and is easily understood. However, the controls soon become familiar after fiddling with the system for an hour or so, and programming is childs play and a very useful addition.

Overall, I was most impressed by this digital delay. It is sufficiently refined for use in the studio and yet its inherent sturdiness and its programmability make it equally suited to a stage environment. Such a well conceived piece of equipment is uncommon and very welcome.

The SDE 1000 retails for £399 inc VAT.

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