A noise gate is a device which in very basic terms is an audio 'on' and 'off' switch; when the gate is open, the audio signal input is present at the output, when the gate is closed, the audio signal is shut off.

But the Psionics noise gate is far more versatile, with controls for adjusting Attack (how fast the gate opens), Release (how fast it closes), Threshold (the level at which the gate closes) and Depth (how much signal is present when the gate is open).

Noise gates are used both in recording studios and live environments. One of their most common uses is when miking up a drum kit. For example, the low and high tom mics would be put through separate noise gates. The threshold level would be set so that the gate would only open when that particular drum is hit. The reason a noise gate is used like this is because it allows each drum to be assigned a track on the multitrack tape (or mixer channel in a live context) thereby giving independent control of drum equalisation and loudness, which would not otherwise have been possible.

A noise gate can also be used to treat the sound of the signal going through it. This can be achieved on a drum machine, for instance, by adjusting the gate to open (attack control) and close very quickly (release control) so that the natural decay of the drum sound is cut off, thus creating a tight, punchy sound.

Layout

The Psionics device contains four separate noise gates built into one 19" rack-mounting unit which is 1¾" (1U) high and 7" deep. The front panel is divided into four channels, with the mains switch on the far right. On each channel, working from left to right is a Gain control (+20dB to +56dB mic mode and -10dB to +26dB line mode) this sets the input level going into the gate. The Threshold control (-40dBv to +10dBv) sets the minimum level at which the gate will close. Next is the Attack control (0.1mS to 20mS) which sets the time taken for the gate to open. Release (0.1 to 6 seconds) determines how long the gate takes to close. The Depth control (0.5dB to 70dB) determines the noise level when the gate is closed, as well as how much signal is present when the gate is open. All controls are of the rotary type with a click turn control which allows for very precise settings, that remain stable when the unit is transported for example.

Above the pots there are three push action switches: a Mic switch which when depressed switches the unit from line level to mic level. The Key switch which allows the gate to be opened and closed by another audio source. Common practice is to use an output from a bass drum mic to open a noise gate through which the bass guitar is being processed. The bass drum opens and closes the gate very quickly thus cutting out the natural sustain the bass guitar might have; the end result is a very tight punchy bass sound. The last switch is a bypass switch labelled 'In', which cuts out the noise gate when depressed, leaving the unprocessed signal.

At the bottom right of each noise gate channel are two LEDs, one green indicating gate open and one red showing that the gate is closed.

Rear Panel

On the back panel looking from left to right, there is an IEC mains socket followed by a voltage selector. Input, Output and Key connections are provided for each channel which are all via male and female XLR connectors. This is the commonest type of connector found on professional recording studio equipment, so if using units with normal signal and ground connections, the signal line must be connected to pin 3 and the ground to pins 1 and 2 when using this device.

A thoughtful feature of this unit is the inclusion of a mono Sum output. This is the combined output of all four noise gates. This means that the unit could easily be used as a submixer. For example, where a drum kit is being recorded using four mics each going into an individual noise gate, their outputs could be summed to provide one overall signal that can then feed a single track of a four track recorder, say. In this way, you don't waste tracks unnecessarily on achieving a 'clean' drum sound. It is also useful where there are a limited amount of channel inputs on a mixer.

As far as operation is concerned the noise gates are fairly easy and quick to set up. With the aid of the click turn pots a precise setting can be obtained.

The inclusion of the mono Sum output is useful when used in conjunction with a four track recording system. These features combined with the two status LEDs on each gate enabled good results to be obtained in a short time.

Conclusions

The Psionics NG4 Quad noise gate is a versatile unit that has been designed for easy and creative use. It has the advantage of having four noise gates in one self-powered unit as opposed to the usual costly method of separate noise gate, rack unit and power supply. The price, however, may be outside the average home recordist's budget, but if you are looking for a space-saving, quality unit that is relatively easy to set up, the Psionics can be recommended.

The NG4 retails at £460 including VAT and is distributed in the UK by Kelsey Acoustics, (Contact Details).