The Valley People KEPEX II is a modular, voltage-controlled programme expander and noise gate developed as the successor to the original KEPEX, introduced in 1969. Designed for professional recording studios, the KEPEX II combines continuously variable downward expansion, noise gating and external keying capabilities in a compact module compatible with the Valley 800 Series powered rack-mounting system. Built around the Valley TA-101 Voltage Controlled Amplifier (VCA), the KEPEX II provided engineers with extensive control over signal leakage, unwanted noise, dynamic range and creative envelope shaping.
The original KEPEX had become an established dynamics processor in professional recording studios, where its ability to attenuate unwanted signals below a selected threshold made it particularly useful during multitrack recording. The KEPEX II represented a substantial development of the original concept, incorporating redesigned circuitry, additional operating controls and the Valley TA-101 VCA. This gain-control element was designed to address problems associated with less sophisticated VCA circuitry, including distortion, high noise levels and non-linear control behaviour.
Unlike a conventional noise gate operating primarily between open and closed states, the Valley People KEPEX II provides continuously variable downward expansion. Its expansion ratio can be adjusted from 1.1:1 to 1:100, allowing engineers to select anything from gentle attenuation of low-level signals to extremely steep gating. At lower ratios, background noise and unwanted leakage can be progressively reduced without abruptly cutting off the programme material. Higher ratios produce more pronounced attenuation, making the processor suitable for isolating drum hits, reducing microphone spill and removing unwanted sounds from individual tracks.
The RANGE control determines the maximum amount of gain reduction, providing adjustment from 0 dB to 90 dB. This allows the engineer to restrict the degree of attenuation even when using aggressive expansion ratios. An adjustable THRESHOLD control, operating from -40 dBv to +20 dBv, establishes the signal level below which the processor begins applying expansion. Together, these controls allow the KEPEX II to be configured for a wide variety of recording and mixing applications.
Five continuously variable front-panel controls provide adjustment of the processor’s operating characteristics. Attack time can be varied from 0.02 ms to 20 ms, enabling the KEPEX II to respond rapidly to transient signals or more gradually to slower programme material. The short attack settings are particularly useful when processing percussion and other sounds with pronounced initial transients. Release time is adjustable from 0.04 to 10 seconds per 20 dB of attenuation, allowing the engineer to determine how quickly the processor reduces gain after the signal falls below the selected threshold.
A dedicated LIN/LOG switch changes the release characteristic between linear and logarithmic operation. In the linear position, the KEPEX II releases at a constant number of decibels per second. In logarithmic mode, the amount of gain reduction increases progressively faster as the release time continues. This behaviour reduces the premature attenuation of naturally decaying sounds while helping prevent the unnatural interruption of passages containing longer decays. The logarithmic setting also reduces modulation distortion when faster release times are selected.
One of the distinguishing features of the Valley People KEPEX II is its external keying facility, which extends its capabilities beyond conventional noise reduction. A three-position MODE switch provides IN, OUT and KEY operating modes. In the normal IN position, the input signal is routed to both the VCA and the internal control circuitry, providing conventional expansion and gating. Selecting KEY routes the main audio signal through the VCA while allowing a separate signal to determine the gain-control envelope. In the OUT position, the audio signal passes through the VCA without being subjected to the expansion or gating control action.
The external keying arrangement allows one signal to control the dynamic behaviour of another, opening up a range of creative processing possibilities. A rhythmic signal, for example, can be used to control the amplitude envelope of a sustained instrument, producing synchronised gating and modulation effects. By altering the attack, release, threshold and expansion settings, engineers can shape the resulting envelope to produce anything from subtle rhythmic movement to pronounced special effects. This capability also makes the KEPEX II useful for envelope following and the dynamic manipulation of recorded sounds.
In conventional recording applications, the KEPEX II can be used to reduce unwanted microphone leakage, particularly during multitrack drum recording where signals from neighbouring instruments frequently enter microphones intended for individual drums. Appropriate threshold, ratio and release settings allow unwanted spill to be attenuated between performances while preserving the desired attack and decay characteristics. The processor can also be used to reduce excessive cymbal ringing, control background noise and tighten the dynamic behaviour of individual recorded tracks.
The KEPEX II incorporates a 13-segment LED gain-reduction display indicating attenuation from 0 dB to 50 dB. This provides a visual indication of the amount of expansion or gating being applied, assisting engineers when setting operating thresholds and adjusting the processor’s dynamic response. Its narrow front panel places all five rotary controls, operating switches and the attenuation display within easy reach.
Designed for installation in either of the Valley 800 Series powered rack-mounting enclosures, the KEPEX II was intended for modular professional studio installations. Multiple modules could be accommodated within a common rack system, allowing individual channels of expansion and noise gating to be assigned to separate recording tracks. This arrangement was particularly suited to multitrack studios requiring several channels of independent dynamics processing without the space requirements of individual rack-mounted processors.
The Valley People KEPEX II illustrates the development of the noise gate from a relatively straightforward noise-reduction device into a more versatile dynamics processor. Its combination of continuously variable expansion, comprehensive attack and release controls, externally controlled keying and modular construction allowed it to perform both corrective and creative functions. As a successor to the original KEPEX, it retained the fundamental concept that had established the product while introducing additional control over the way recorded signals were processed.
Features
- Modular keyable programme expander and noise gate designed for professional recording applications.
- Valley TA-101 Voltage Controlled Amplifier (VCA) circuitry.
- Continuously variable expansion ratio from 1.1:1 to 1:100.
- Adjustable threshold from -40 dBv to +20 dBv.
- Variable attenuation range from 0 dB to 90 dB.
- Independent attack and release controls.
- Switchable linear and logarithmic release characteristics.
- External keying facility allowing one audio signal to control the dynamic envelope of another.
- Three-position IN, OUT and KEY operating mode switch.
- 13-segment LED gain-reduction display.
- Suitable for noise reduction, microphone leakage control, dynamic expansion and creative envelope processing.
- Compatible with Valley 800 Series powered rack-mounting enclosures.