The Allison Research Gain Brain 700 was released in 1971 as a professional level control module for studio recording applications. Designed as a card-format processor with a high-impact plastic front panel, controls and metering, the Allison Research Gain Brain 700 provided limiting with a distinctive dual-threshold system that allowed operation between peak limiting and quasi-RMS limiting.
The front-panel Function control determined the relative action of the peak and RMS thresholds, with the unit functioning as a peak limiter in the full counter-clockwise position and as a quasi-RMS limiter in the full clockwise position. In practical use, Allison Research recommended setting the Function control near the centre position, allowing transients and complex waveforms to trigger peak limiting while sustained waveforms were limited according to their apparent level energy.
The Allison Research Gain Brain 700 was built around a simple control layout that gave engineers direct access to input gain, output level, release characteristics, limiting mode and gain reduction metering. The Input control established the threshold of limiting, while the Output control set the required output level. The Release control adjusted recovery characteristics, with faster release times producing a higher apparent level and longer release times producing a more natural dynamic range.
The manual also noted that as the Function control was rotated towards the RMS position, the actual release time became longer than the panel calibration, particularly at faster release settings, helping prevent low-frequency sustained waveforms from causing excessive distortion.
Metering was central to the operation of the Allison Research Gain Brain 700. The front-panel meter indicated gain reduction in dB, while dedicated Peak and RMS indicators showed when limiting was taking place and which type of limiting was active. The gain reduction meter used a seven-increment sequential light-emitting diode array, displaying gain reduction from 2dB to 24dB, and was described as virtually instantaneous for accurate reading of short-duration, fast-release limiting.
The Allison Research Gain Brain 700 accepted programme material at levels between -20dBm and +20dBm and offered a gain reduction range of 30dB. Its limiting ratio was approximately 50:1 in peak mode and approximately 40:1 in RMS mode, with the Function control allowing variable separation between the thresholds from 0dB in Peak position to 12dB in RMS position. The module also provided multiple limiter coupling for tandem limiting, making it suitable for linked operation where required.
The Allison Research Gain Brain 700 was designed for modular installation. It was compatible with Kepex 500 modules and could be installed in Allison Research enclosures, including the CM-001 single-channel console mounting case and the RM-160 rack mounting card library.
The CM-001 was intended for console and custom installations where one or a small number of Allison Research Gain Brain modules were needed, while the RM-160 accepted up to 16 Gain Brain modules and included an integral power supply and plug-in power switching card. Audio connections were unbalanced, with a 3k ohm input and 150 ohm output.
Features
- Professional level control module for studio recording applications
- Peak limiting and quasi-RMS limiting operation
- Function control adjusts the relative action of peak and RMS thresholds
- Centre Function settings allow transients to trigger peak limiting while sustained waveforms follow apparent level energy
- Input control establishes the threshold of limiting
- Output control sets the required output level
- Release control adjusts recovery characteristics
- In/out switch removes the limiting networks from operation while retaining input and output level controls
- Gain reduction meter calibrated in dB
- Peak and RMS indicators show which limiting action is taking place
- Seven-increment sequential LED gain reduction meter
- Multiple limiter coupling connection for tandem limiting
- Compatible with Kepex 500 modules
- Compatible with CM-001 single-channel console mounting case
- Compatible with RM-160 rack mounting card library for up to 16 modules
