The piece of audio processing equipment known as a ―gate‖ is also referred to as a ―noise gate‖ which refers to its commonly used function as a noise-reducing audio processor. In simple audio terms, a gate allows an audio signal to pass through to its output until it falls below a certain threshold level, at which point it mutes the audio – this processing action is known as ―gating‖ the audio signal. Companies such as AMS/Neve and Universal Audio produced
professional quality gates in the 1960s and 1970s, which were used both in recording studios and in live sound mixing consoles. Live sound mixing in particular made use of the gate to reduce the leakage of unwanted sounds or noise into the onstage microphones.
While the audio hardware originally used for gating techniques is still in use in major recording studios, the development of digital audio plugins that achieve the same functionality has largely taken over from their hardware counterparts. The software versions of contemporary gate effects are capable of much more complex and tempo-synced functions since they are dependent only on the underlying computer processing power and digital audio soundcard, as well as the host software. Universal Audio in particular, while still producing high quality hardware versions of its various preamplifiers, dynamics processors and equalizers, has transformed itself into a producer of sought-after software versions of many of its classic
devices, at a much lower cost.
The gating parameters usually included on a standard gate device, whether an analog or digital version, are outlined in Table 2. A standard gate plugin, in this case from the Cubase DAW, is depicted in Figure 41.
Table 2: Gate audio processing functions
Function Description
Threshold Level Determines the level of incoming signal that opens the ―gate‖ to allow the signal to pass through and be heard
Attack Controls the speed at which the gate opens once the threshold has been met Hold A supplementary control which allows the gate to stay open for a certain
time after the signal has fallen below the threshold
Release Controls the speed at which the gate closes once the level falls below the threshold
Range Attenuates the audio signal level when the gate is shut. When set to infinity, the gate is completely closed and allows a zero amount of the audio signal through
Standard gates are able to interact with any incoming audio that is directed to its input, and using the controlled parameters, the audio engineer is able to engage several useful functions in regards to the live performance, recording, and studio mixing of music. A typical use of the standard gate by a sound engineer would be to add a gate to a guitar audio channel on a mixing board, where the guitar amplifier is heard through a microphone positioned against the guitar amplifier. Guitar amplifiers often produce audio noise, signal interference, or other low-level buzzes, hums, or static. The gate threshold would be set so that when the guitar is playing an actual passage, the audio from the microphone would be allowed to pass through to the mixer channel, but would be muted once the passage ended so that the extraneous guitar amplifier noises and hums would not be heard. This technique helps to clean up the overall sound mix by muting these erroneous noises.
The various gate parameters (attack, release and hold) would be set according to the individual performance, so that the gating function would not unnaturally cut off notes at the end of a phrase or suddenly open too quickly, creating a clipped opening note. Other typical
functions of a standard gate would include muting any sympathetic tones of drumset tom-toms when not actually being played, or a vocalist’s microphone during a live performance with an ensemble when they are not singing, preventing extraneous sounds from leaking into the overall mix.
While these functions are certainly useful to an audio engineer for both live performance and recording, a more advanced feature known as a ―sidechain input‖ opens up more creative and musical possibilities that are in common use in electronic dance music. The ―sidechain‖ function allows a separate audio source to act on a gate assigned to a different audio channel. In other words, the gate assigned to channel ―A‖ would have its threshold parameter activated by channel ―B‖ with a corresponding result in channel ―A‖’s audio output, while ―B‖ is not heard at all on channel ―A,‖ instead acting as an invisible actuator of the gate’s threshold function. Since the sidechain input can consist of any audio source sent to an appropriate gate, many musical possibilities exist for the creative use of gating techniques, especially when used in modern audio software.
For example, a sustained chordal sound, such as synthesizer string sound, can be given rhythmic qualities by enabling a gate using a sidechain input from a rhythmic source, such as percussion instruments. The chordal ―pad‖ sound would now mimic the rhythmic patterns played by the percussion part, in any degree from sharply accented to more subtle. The trance genre uses a well-known version of this technique known as a ―trance gate‖, achieved by
sidechaining a synthesizer pad from a triggered kick drum or other rhythmic percussive element, as heard in The Age Of Love’s“The Age of Love‖ (1992), BT (Brian Transeau)’s ―Tripping the Light Fantastic‖ (1995) and Robert Miles’ ―Children‖ (1995).
In modern hip-hop and EDM audio production, a common technique involves the use of a kick drum sample supplemented by a low subsonic sine wave layered underneath. In this scenario, a constant sounding low sine wave in the 50-60 hz range is produced on an audio channel using a plugin sound oscillator or tone generator. A sine wave is a preferred choice since it contains less harmonic overtones than a more complex saw or square wave and will blend smoothly. Once a gate is enabled on the ―sine kick‖ channel, its’ sidechain function is enabled, triggered by a separate kick drum part. The input, attack, hold and release parameters are
adjusted until the kick drum and sine wave sound as one voice, resulting in a kick drum part with a subsonic undertone.
Another contemporary technique using gates is a ―microstop‖ or sudden muting of the entire stereo music mix. Used to create sudden tension as the music drops away, a gate is applied to the entire sound mix as a master effect. At a strategically climactic moment, usually just before a strong chorus of the song, the gate can be enabled through the sidechain by either a kick drum or other unused part, or through the host software’s automation. The result is an abruptly dramatic moment of silence before the next section of music crashes in.