The Aphex 105 Logic Assisted Four Channel Gate is a four-channel analogue noise gate designed for recording studios, live sound reinforcement and professional audio installations. Incorporating Aphex’s proprietary VCA 1001 attenuation circuitry, Logic Assisted detection and Peak Stretch processing, the Aphex 105 provides independent control over threshold, attack, hold and release for each channel. Developed as a streamlined alternative to the company’s 622 Logic Assisted Expander/Gate, it combines established Aphex gating technology with straightforward operation in a compact 1U rackmount enclosure.
The Aphex 105 was introduced by 1994 as part of the company’s ST (Serious Tools) series of professional audio processors. Its development followed a history of noise-gating technology at Aphex, beginning with the Aphex 612 Expander/Gate. In 1987, Aphex issued a $10,000 challenge to competing manufacturers to produce a gate capable of outperforming the Aphex 612. The company subsequently introduced the Model 622 Logic Assisted Expander/Gate in 1993, incorporating advances in detection circuitry and attenuation control.
Recognising that some users did not require the full range of facilities offered by the Aphex 622, Aphex developed the Aphex 105 as a lower-cost, simplified alternative. The new processor retained several of the Model 622’s principal technologies while offering four independent gating channels with a straightforward control arrangement. Its design concentrated on the essential functions of noise gating, allowing unwanted signals to be attenuated without introducing unnecessary complexity into the recording or mixing process.
Central to the Aphex 105 is the company’s proprietary VCA 1001 Voltage Controlled Attenuator. This circuit controls the attenuation applied to each audio channel and was designed to maintain low distortion and minimise control feedthrough during rapid gain changes. In conventional noise gates, abrupt opening and closing can introduce audible clicks or pops, particularly when processing transient signals. The VCA 1001 addresses this problem through its low control feedthrough characteristics, allowing the gate to operate rapidly while minimising unwanted switching artefacts.
The Aphex 105 also employs Aphex’s Logic Assisted detector circuitry, developed to provide positive, stable and accurate triggering regardless of the selected attack time. In a conventional gate, changes to the attack setting can influence how the processor responds to incoming signals. The Logic Assisted circuit separates the triggering function from the attack adjustment, ensuring that the gate opens reliably whenever the incoming signal exceeds the established threshold. This allows the operator to adjust the gate’s opening characteristics independently of its detection behaviour.
Working alongside the Logic Assisted detector is Aphex’s proprietary Peak Stretch circuit. This processing increases the effective level difference between unwanted background noise and the desired programme material, helping the detector distinguish between signals that should open the gate and those that should remain attenuated. The combination of Logic Assisted detection and Peak Stretch processing provides consistent triggering and reduces unwanted gate operation when working with material containing varying signal levels.
Each of the four independent channels provides Threshold, Attack, Hold and Release controls. The Threshold control establishes the signal level at which the gate opens and closes, with an adjustment range from -50dB to +20dB. When the incoming audio or external key signal exceeds the selected threshold, the gate opens and the corresponding Open LED illuminates. When the signal falls below the threshold and the hold period has expired, the gate begins closing and the Closed LED indicates its status.
The Attack control determines how quickly the gate opens, with an adjustment range from 200µs to 120ms. Faster settings allow the processor to respond to rapid transients, while slower settings provide a more gradual opening characteristic. The Hold control introduces an adjustable delay between 1ms and 1 second before the release circuit becomes active, preventing the gate from closing prematurely during short pauses or decaying sounds. The Release control determines the speed at which attenuation is restored, with settings ranging from 100ms to 4 seconds.
A switchable attenuation range allows the operator to select between 6dB and 90dB of attenuation when the gate is closed. The 6dB setting provides a moderate reduction in unwanted signal levels, allowing some background ambience to remain audible. The 90dB setting provides substantially greater attenuation for applications requiring unwanted signals to be effectively muted. This flexibility allows the Aphex 105 to accommodate different recording and sound reinforcement requirements.
Each channel also incorporates an external key input, allowing the gate to respond to a separate triggering signal rather than the audio passing through its main input. Inserting a connector into the rear-panel External Key socket automatically transfers detector control to the external signal. A dedicated front-panel LED indicates when an external key connection is present. This facility allows the Aphex 105 to perform externally triggered gating, including synchronised effects and the selective control of one audio signal by another.
The rear panel provides individual operating-level switches for each channel, allowing selection between professional +4dBu and -10dBV signal levels. The audio inputs accommodate active balanced operation at +4dBu and unbalanced operation at -10dBV, while the outputs employ a pseudo-balanced configuration. Input, output and external key connections are provided through 6.35mm TRS sockets, allowing the processor to be integrated into a variety of recording and sound reinforcement systems.
In multitrack recording, the Aphex 105 could be used to control microphone leakage, attenuate amplifier noise and mute unused signal paths. During mixing, its four independent channels allowed several instruments or audio sources to be processed simultaneously. In live sound applications, the processor could reduce the contribution of unused microphones, helping to minimise unwanted background noise and feedback. Additional applications included automatically muting unused synthesisers and sound modules, controlling microphones in conference installations and using external signals to trigger gating effects.
The Aphex 105’s published performance specifications include a frequency response of 17Hz to 20kHz within ±0.1dB, dynamic range exceeding 120dB and total harmonic distortion of 0.005% at 1kHz. Crosstalk rejection is specified as better than 90dB across the 20Hz to 20kHz audio spectrum. The four channels are housed in a 1U rackmount enclosure, with power provided by an external 24V AC transformer.
The Aphex 105 represents a streamlined implementation of the company’s established noise-gating technology. By combining the VCA 1001, Logic Assisted detection and Peak Stretch processing with four independently adjustable channels, it provided a practical means of managing unwanted signals in analogue recording, mixing and live sound environments.
Features
- Four independent analogue noise gate channels.
- Proprietary Aphex VCA 1001 Voltage Controlled Attenuator.
- Logic Assisted detector circuitry for stable, accurate triggering.
- Peak Stretch processing to improve discrimination between desired programme material and unwanted noise.
- Independent Threshold, Attack, Hold and Release controls for each channel.
- Adjustable threshold from -50dB to +20dB.
- Attack time adjustable from 200µs to 120ms.
- Hold time adjustable from 1ms to 1 second.
- Release time adjustable from 100ms to 4 seconds.
- Switchable attenuation range from 6dB to 90dB.
- Individual Open and Closed LED gate status indicators.
- External key input for each channel, allowing triggering from a separate audio signal.
- Dedicated External Key LED indicator on each channel.
- Individual -10dBV/+4dBu operating-level selection.
- Active balanced inputs and pseudo-balanced outputs.
- 6.35mm TRS audio and external key connections.
- Compact 1U rackmount design with external power supply.