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Rebis Effects Rack


Rebis have managed by careful design to produce high quality audio processors at a price that puts them within reach of serious home users as well as professional studios. Paul White takes a look at the system and the philosophy behind its design.


The Rebis Rack is not, as its name may imply, an instrument of torture from the Spanish Inquisition, but an economical system for mounting and powering modular signal processors.

Until recently, most studio outboard gear was packaged in separate rack-mounting cases, each with its own power supply, but this approach is both costly and wasteful. Even with a well designed circuit, the case and the power supply may cost more than the electronics and, as most units can be designed to run from the same supply voltages, it clearly makes sense to use one power unit to drive several modules.

The 19" wide Rebis Rack will house up to fourteen effects modules in addition to the power supply, and connection to the rack may be made by means of phono connectors, hard wiring, or a system of 'A' type jack sockets that come in blocks of four per module for front panel access. Additionally, for a very modest extra cost, the rack can be custom-wired so that the modules are pre-patched or normalised unless a jack is inserted to break the chain, and this is particularly useful for the situation where a combination of several modules is generally dedicated to a specific task such as the delay system which may comprise up to four modules.

The present design is the culmination of over a decade's worth of expertise and experience during which time the original team of three design people has been expanded to eleven. As with most success stories, Rebis started out from humble beginnings by building a single mixing desk for Mike Oldfield, and from there, things escalated until now, Rebis are exporting most of their output to studios throughout the world.

Construction



The rack itself is a simple but well engineered affair based on the Vero card frame system. Modules fit into plastic guides and connect via gold-plated edge connectors to sockets mounted on a printed circuit backplane which also houses the phonos if fitted.

Three modules in width, the power supply fits into the end slot of the rack and, even though this contains a toroidal transformer, it is well screened to prevent hum pick up.

The individual modules consist of a PCB mounted onto the front panel and a screening plate is used to prevent crosstalk between modules. There is a bewildering choice of modules available from Rebis but the ones that we checked out are as follows:

RA 202 De-esser



The De-esser is designed essentially to reduce sibilance (overemphasis of 'ss' sounds) by means of a compressor, the control circuit of which is frequency selective, responding only to frequencies in the five to twenty kilohertz range. The only operator-variable control is the threshold setting; attack, release and ratio all being preset. A bypass switch is fitted so that A/B comparisons can be quickly made.

Compression is applied to the whole audio band so that the breath noise also associated with sibilance is also suppressed.

It is only practical to treat one vocal track at a time so one RA-202 will be needed for each vocalist or vocal track being processed.

In use, the unit performed well providing that the threshold was set up carefully and no ill effects were experienced. De-essers are not a complete cure for bad mic technique but they can be a great help. Noise was at no time evident which of course is as it should be. The quoted noise spec is -80dBm.

RA 204 Parametric EQ



This is a single, three parameter filter which has an additional level control and LED peak indicator to prevent overloads at high resonance settings.

Frequency, resonance and EQ range may be adjusted, the latter allowing +/-21dB of boost at the centre frequency. The frequency pot covers a 100:1 range and a x10 switch enables the centre frequency to be set anywhere from 20Hz to 20kHz.

A bypass switch is again fitted and the unit behaved smoothly with no bad habits or undue noise. At unity gain, the specified output noise is -80dBm.

Parametric EQs may be used to tune out annoying peaks in the programme material and are even helpful for reducing mains hum which may have crept onto a recording. Apart from such salvage jobs, they may also be used to create special effects or for applying EQ in strategic areas where the mixer EQ may be inadequate.

RA 201 Noise Gate



The Noise Gate is really a voltage controlled amplifier which shuts down gracefully when the input signal falls below a specific threshold level, and its popular uses are the removal of tape noise or low-level background noises such as the rustling of lyric sheets or managers' wallets!

By feeding the provided key input from a separate source, the gate may be used creatively to gate one sound in the presence of another, and an example of this is where a snare drum beat opens the gate and allows a burst of reverb to pass through in order to create the 'gated reverb' sound currently in vogue.

Controls for attack and release times are fitted in addition to the threshold adjustment and a further control labelled attenuation sets the amount of gain reduction when the gate is in its 'off position.

Again a bypass switch is fitted, and the key switch allows the control circuitry to operate from either the signal input or an external key input.

No problems were experienced in use (honestly!) and a pair of LEDs, one green and one red, show whether the gate is open or closed.

As with all noise gates, care must be taken to select the correct threshold level to avoid losing chunks of wanted sound and a degree of experience is necessary in order to select attack and release times suitable to the material being processed. Specified output noise is -92dBm.

RA 203 Compressor-Limiter



The Compressor reduces the dynamic range of any signal exceeding a set threshold level, below that level, the signal passes through unchanged. A set of four LEDs indicates the amount of compression taking place and the compression ratio may be set anywhere between 1:1 and 40:1. Set at 40:1, the unit becomes a Limiter and the signal will not be permitted to become any greater once it has reached the threshold level.

A bypass switch is fitted along with a link switch which allows two compressors to work from a common control signal for stereo applications.

Controls are provided, for sensitivity, compression ratio, release time and attack time, although surprisingly, the maximum attack time is only 1.5 milliseconds which limits the creative uses of the device where a long attack time can help to create punchy percussive sounds from bass guitar or drums.

Again, care has to be exercised in setting the parameters but once optimised, the unit is quiet and unobtrusive. Quoted noise is better than -75dBm with the sensitivity control set to 0dBm.

Delay System



This comprises three modules centred around a short duration, high quality analogue delay circuit.

The basic RA 205 delay module features a maximum delay time of 40ms which may be doubled at the expense of a reduction in bandwidth and a compander type noise reduction system is fitted. As companders can have adverse effects on some types of programme material, a control has been fitted to reduce the severity of the noise reduction so that a compromise between noise and transient response may be achieved for all types of signal.

A further control adjusts the balance between direct and delayed signals and a feedback control enables some of the delayed signal to be recycled.

This module may be used on its own to provide pre-reverb delays, for example, but when used in conjunction with the RA 208 Modulator module, chorus and flanging may also be obtained, there being a choice of square, triangle or sine waveforms over the frequency range of 15Hz to 0.003Hz, a useful pair of LEDs being used to indicate the oscillator frequency.

An offset control enables waveforms to be clipped for special effects and a hold switch freezes the output voltage at its current level until released. The modulation waveform may be routed to one or two RA 205 Delay modules and the RA 209 Mixer module makes even more ambitious effects possible.

RA 209 Mixer



When using two delay modules, the RA 209 provides all the mixing, phase inversions and level controls necessary to create a wide variety of special effects. The unit incorporates two level and two feedback controls as well as switches for phase reversal and series/parallel connection of the delay lines. Using this module, stereo delay, chorus, vibrato and flanging may all be produced.

Although this is an analogue delay line, it is very quiet in use and the effect bandwidth of 15kHz makes it suitable for the most discerning of applications: The noise figure of the delayed signal is —74dB which accounts for its quiet operation and, although the delay is far too short for true repeat echo effects, it is ideal for all the other time domain effects and the versatility of the three module system (or four with two delay modes) is quite remarkable.


Conclusions



Although these are not particularly expensive effects as studio quality units go, they perform well and have no strange habits that I could find. The rack concept keeps the price down and the company's philosophy is to provide good back-up service at minimal cost when required (which is rarely).

It's nice to see British firms competing on a world-wide scale with oriental manufacturers in this field and this can only be a further testimony to the quality, reliability and value for money of these products.

Rebis are not content to rest on their laurels, however, research is an ongoing process and new modules are being added all the time. By the time that you read this, their new Filter Gate should be available which incorporates sidechain EQ for frequency selective gating and the filter section may be isolated for separate EQ'ing applications if required.

The 14 channel Rack Frame retails at £120.75. The VAT-inclusive prices for the reviewed modules are as follows: Noise Gate £81.65; De-esser £98.90; Compressor-Limiter £148.35; Parametric EQ £85.10; Delay £155.25; Modulator £81.65 and 4 way Jack module £17.25.

For the full rundown on all other modules please contact: Rebis Audio, (Contact Details).



Previous Article in this issue

Visonik David 6000

Next article in this issue

QSC Audio Model 1400 Power Amplifier


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

 

Home & Studio Recording - Sep 1984

Donated & scanned by: Mike Gorman

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Gear in this article:

Studio FX > Rebis Audio > RA200


Gear Tags:

MultiFX

Review by Paul White

Previous article in this issue:

> Visonik David 6000

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> QSC Audio Model 1400 Power A...


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