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Long Delays Aren't Always Bad News


A sampling delay line with a very long memory, this time from DOD.

The Digitech Sampling Delay offers a stylish rack mounting delay package that can also double as a triggered sampler.

With the profusion of digital delay units currently available, you might wonder why manufacturers keep bringing out new ones, but there's more to this one than meets the eye. Produced by DOD, the RDS3600 offers 1.8 seconds of delay at full bandwidth, but when the need arises, the delay time may be extended to 3.6 seconds or even 7.2 seconds by means of a switch on the rear panel although you'll suffer from the inevitable trade-off in high frequency response. Additionally, sounds may be sampled into the unit and triggered via an input on the rear panel though there is no provision for controlling the pitch of the stored sound in any musical way.

Cosmetically, the 1U package is styled very much along the lines of Lexicon equipment with large areas of pale blue screened onto the black front panel and very classy it looks too. Even the square buttons look typical of Lexicon, far be it from me to censure the morals of the manufacturers on this point.

Modulation controls are provided so that all the standard DDL effects may be set up and the Feedback control is of the centre-off type which offers both in and out of phase regeneration.

Unusual on a machine of this price is a 4-digit LED display which monitores the Delay time in milliseconds and the Delay time itself is set up by using a combination of four push-button switches and a rotary control.

To sample a sound, a pulse must be applied to the sync socket to initiate the process and when the sound has been captured, depressing the Repeat Hold switch locks it into memory. Subsequent pulses such as those produced by drum machine trigger outputs cause the stored sample to be replayed. Though there is no CV or MIDI input that can play the sample back as musical notes, there is an external modulation input that takes the output from a suitable Low Frequency Oscillator if you want to experiment with alternative modulation waveforms.

Rear Panel

As you might expect, the back panel houses the Input and Output jack sockets and of course the Sync socket but there's more. There are separate Dry and Mix outputs, and there is an additional Mix output with inverted phase (of the delay component) for creating pseudo stereo effects, although this is not recommended when recording as the system is not mono compatible; the effect cancels to nothing when the two outputs are summed together. Further jacks are fitted for the connection of footswitches, one to control the Repeat Hold function and one to kill the delayed sound. The remaining two sockets are for the Sync input and the Modulation Control Voltage.

A three way slider switch adjacent to these sockets sets the maximum delay time and it is the location of this switch that leaves the design open to criticism; if the unit is rack mounted, this switch is difficult to get to.

"As a sampler, the RDS3600 works perfectly well given that there are no editing facilities and no sound operated trigger."

Control Topography

Input works in conjunction with a four section LED level display to match the input signal to the following circuitry. A high input impedance of 470K ohms means that either line level signals or instrument outputs can be accommodated. The signal to noise ratio of the delayed signal is 85dB resulting in very quiet operation and the Effect button mutes the delayed sound when activated.

Modulation covers a range of 0.6Hz to 6Hz and the modulation oscillator can sweep the delay time over a 9:1 range for the production of vibrato, chorus and flanging. This section is overridden when an external modulation source is connected.

The Delay Time section comprises four buttons, each with their own status LED, that get you into the right ball park and then the Delay Time control itself can be adjusted to get the exact delay time required. The display is a great help here, though the four buttons are marked Flange, Chorus, Double and Echo if you're in any doubt as to where to start. When the ranges are switched, the delayed signal is muted for two seconds to prevent bursts of unwanted sound appearing at the output.

The Display is a seven segment red LED display showing the Delay Time in milliseconds, and this registers any changes in the Delay Time caused by the modulation section. The adjacent Kill LED shows when the rear panel Kill function has been activated by a footswitch.

The Repeat Hold function freezes whatever sound is currently in the memory for infinite looping or one-shot triggered samples. The state of this switch is indicated by a status LED.

As far as feedback goes, up to 100% feedback may be applied in either phase to give near infinite repeat echo or deep flange type effects. The choice of phases is only significant at short delay times and is most noticeable on flanging effects.

Mix balances the proportion of Dry and Delayed signal. When used with a mixing desk, this control would normally be fully clockwise so that the output contains only delayed signal.

"...the RDS3600 offers a lot of high class features for an affordable price, especially if you like to use long delay times."

Lastly, the Output Level control allows the output to be set at any level up to +18dBv. The minimum load impedance is 600 ohms at which point the maximum output level falls to +14dBv. The inclusion of the display readout is a great help in consistently setting up effects, provided of course that you keep a record of such things and the fact that it monitors the effect of the modulation control can be useful (see the 'Phase the Music' article in this issue).

As a sampler the unit again performs well within its limitations but I would have liked to have seen some musical control over the pitch of the stored sound such as a one volt per octave input that could be driven by a mono-synth. Also a sound activated trigger would have made it easier to synchronise the sampling procedure with the sound being captured but with a bit of practice, things work well enough the way they are.

In Use

There was no problem in getting this unit to produce any of the standard delay effects but one could question the wisdom of fitting the range change switch to the rear panel as this makes it very difficult to operate when the unit is mounted in a rack as I predicted during the introduction.

Background noise was not a problem as it is with some budget digital units and the bandwidth at the shortest delay setting was impressive. Even at half bandwidth/double delay, the sound quality was not at all bad, but in the last position the sound is definitely losing a lot of its definition. Still, its handy to have this option and you can always use your trusty psycho-acoustic enhancer to perk up the top end.


With a 16kHz bandwidth, the basic delay of 1.8 seconds is generously long but the option of longer delays at restricted bandwidths can be useful under certain circumstances. When the maximum delay time is extended to 7.2 seconds, the bandwidth is reduced to a mere 4kHz which as previously intimated is a little low for most serious uses though it is no worse than the performance offered by a typical analogue delay pedal unit.

As a sampler, the RDS3600 works perfectly well given that there are no editing facilities and no sound operated trigger. Also it would have been nice to be able to play tunes with the sample and that shouldn't be too much to ask for the price.

Although the RDS3600 costs a little more than a bog standard DDL, it makes a very attractive package and the quality of its modulation based effects is particularly good, due in part to its 9:1 modulation ratio. The bottom line is always the question of value for money and the RDS3600 offers a lot of high class features for an affordable price, especially if you like to use long delay times. You are however paying for the extra delay time and the triggering facility and if you don't need these, DOD do a much more cost effective version in the form of the RDS1900. This identically styled unit gives you 1.9 seconds of delay with a 15kHz bandwidth but there is no triggered sampling, no external modulation input and no way of increasing the delay time. Even without these facilities, the RDS1900 does give a long delay of very high quality for the modest inclusive price of £251.85 and it can create all the usual modulation effects with ease.

The DigiTech RDS3600 costs £433.15 and is available from Sound Technology Ltd, (Contact Details).

Previous Article in this issue

Millstream Studio

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Sony D50 Compact Disc Player

Home & Studio Recording - Copyright: Music Maker Publications (UK), Future Publishing.


Home & Studio Recording - Nov 1985

Donated & scanned by: Mike Gorman

Gear in this article:

Studio FX > Digitech > RDS3600

Gear Tags:

Digital FX

Review by Paul White

Previous article in this issue:

> Millstream Studio

Next article in this issue:

> Sony D50 Compact Disc Player...

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