Rockman Stereo Chorus/Delay

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There are tenth of chorus effects and dozens of delays on the market. But there is no other device like the Rockman Stereo Chorus/Delay.

Its sonic quality is outstanding, and the features of this half-rack makes it truly different from any other device. One may think that the unit is a classic chorus and delay, packed inside the same enclosure.

It is actually a chorus or a delay: it was done on purpose, thus making the Rockman Chorus/Delay a complete space-maker, rather than one more effect machine.

Objective and history

If you have read in details the section called Rockman - The concept, you know what a chorus is made for, and you also know the role of a slight delay during a recording process.

Both of them are here to switch from the dry mono sound provided by a guitar to a stereo sound, a sound with air and depth.

That's the objective of the Chorus/Delay: it can provide the classic doubling effect of a chorus, that simulates the presence of two guitars playing together, but as a delay, it can also give dynamics and depth by using very short echo sounds (within the 200ms range).

The Chorus/Delay was issued with the Sustainor 100, in January 1986. This second blue-face Rockmodule was produced until the last quarter of 1987, and was replaced by two units: the Rockman Stereo Chorus and the Rockman Stereo Echo. These new items didn't make the Chorus/delay obsolete - just different.

Inside the Module

The heart of the Chorus/Delay is the MN3005 BBD chip. A BBD is the basis component of all the analog chorus effects (25ms delays with an excellent Signal to Noise ratio). It can be pushed up to 200ms delays, at the price of a S/N degradation: 75dB only at the longest delay setting.

In order to improve this poor S/N ratio, SR&D has included in the Chorus/Delay a noise-reduction circuit, based on the same principle as the Dolby System: a "compandor".

A compandor is a dual circuit composed of 1) a compressor before the source of noise (the BBD in our case), 2) an expandor after the source of noise.

The expandor increases the level difference between the sound signal level and the noise level. The signal-to-noise ratio is highly improved, but the dynamics of the sound signal is of course altered. That's why there is a compressor placed before the BBD: the combined action of the compressor and the expandor is neutral for the sound signal, while the noise level is highly reduced.

This compandor system is too expansive for the common chorus and delay stompboxes, and are found only in costly units. It is clearly one of the qualities of the Chorus/Delay, that makes the difference with its competitors.

Back to what the Rockman Stereo Chorus/Delay does: Stereo, Chorus and Delay...

The chorus effect is achieved by sending the original sound through a 20 to 40ms delay, slightly modulated (e.g. 20 to 25ms) then mixing that with the original sound. The result sounds like two guitars playing together.

In order to have a stereo image, one must separate the original signal and the delayed signal, send one of them to the left channel, the other one to the right channel.

That's the widest stereo image you can have, and that's what the common stompbox chorus do not: these pedals are designed to be mono-compatible, so their main output delivers the sum [original + delayed] signal.

When the manufacturer wants to build a so-called stereo image, the other output is only the difference [original - delayed] signal. This is not full stereo, and that's the other significant difference between the Rockman Chorus and the other devices.

All the Rockman Stereo units (Chorus/Delay, Stereo Chorus and Stereo Echo) have a specific output stereo mixer, that allows tweaking the wideness of the stereo image, from mono to wide stereo.

The two following samples allow comparing the stereo image of a Rockman chorus with the TC Electronics Stereo Chorus-Flanger, which is supposed to be an excellent pedal. You will make your opinion by yourself...


TC Electronics SCF

Rockman Chorus







SR&D added another feature in the Chorus/Delay: the delay of the BBD, usually 20 or 25ms in a chorus, can be doubled and be set at 40ms. This is the limit between doubling (when the ear cannot separate the two sounds) and a delay (the human ear clearly hears two disctinct sounds). This Long-Chorus mode provides a deeper effect than the normal mode.

As for the delay section of the Chorus/Delay, we have here a conventional delay/feedback/level set of sliders. The delay time, as said above, can go up to 200ms: coupled with the output stereo mixer, this allows building all sort of reverbish or slap-back stereo sounds.

Usage, samples and limitations

The main usage of the Stereo Chorus/Delay is of course the classic Rockman chorus sound (for a guitar, a keyboard or even connected to a mixer). The following samples illustrate the wide panel of possibilities of the unit.

Mono chorus

Dry sound, then normal setting, then long-chorus. Mono mix for a deeper effect

Stereo chorus

Dry sound, then stereo effect

Delay section

Dry sound, then stereo short slapback, then reverbish sound

The only limitation of the Chorus/Delay is the lack of footswitches: it has only a bypass, a chorus/delay selector and an output mix selector. The other features (long chorus, long delay) are not remote controled.

Collectibility and conclusion

The Chorus/Delay is fairly easy to find (6800 units). It is an excellent value for someone who wants this Rockman Chorus sound, and its delay functions compensate for the simplicity of its chorus section.

Copyright 2008