• Dynamics Processors : Noise gates (expanders)

    4. Ajustes de la puerta de ruido en función de las aplicaciones

    Before using a gate, we need to connect it in the right place. If we use it in combination with a mixer, we will connect it to an insert point, such that will send the original signal and return the gated signal. The insert outputs are always pre-fader, which means we do not have to change the gate's threshold every time the fader position is changed. If we do not have enough gates for every channel, we could also insert a gate on mixer subgroups carrying similar signals (for instance, a brass section). If we use compressors in the same channel that has a noise gate inserted, we will insert the gate first; otherwise the reduced dynamic range of the compressed signal will make adjusting the threshold on the noise gate very difficult.

    Another recommendation is to avoid gating a signal with reverb, as the effect is normally very obvious.

    In general, the criteria in this article are given as overall guidelines and starting points, but they will depend on the specific noise gate or expander model and they may have to be fiddled with by ear

    Voices
    Words may start with a soft vowel sound or, alternatively, with a percussive consonant such as "p" or "t". The attack time should therefore be fast for vocals, but not too fast that produces an audible "click" when opening the gate. Slow attack times loose the attack of the starting consonants and reduce intelligibility, making it difficult to understand the first word after a pause. A time around 1 millisecond is a good compromise solution.
    As far as the decay time, around 0.5 seconds works well keep the noise under control and yet not truncate the end of the words. Sometimes the gate will tend to open and close if there is a signal whose level happens to oscillate around the threshold level. In those cases we can use the "hold time" to avoid that.
    As far as the threshold, use the lowest level possible, though with the risk of background noise opening the gate, experimenting may be needed to set the optimum threshold level.

    Electric guitar
    Electric guitars in general, particularly Stratocaster type ones with single coil pickups that act as aerials for the interference that might exist in the room, produce a lot of background noise. Sometimes the position and orientation of the guitarist helps minimizing the noise, though this is not easy to do in a live concert. Also, distortion and other effects count on using a lot of gain before clipping the signal, which also amplifies any hiss and hum that might have been already present. All of which makes electric guitars very good candidates for gating.
    There are many types of guitars and guitar sounds, as well as many ways of playing them, so attack and releases times will vary widely. A guitar with a lot of sustain may need a decay time as long as 1 seconds, while for a clean percussive sound 50 ms may be sufficient.

    Percussion
    When a drum kit is closed miked using individual microphones for each instrument, every channel is often gated to improve instrument separation, since instruments leak into adjacent microphones. The threshold level may have to be quite high, and we will have to be careful to to miss the quieter hits. The task is simplified if we have a gate with filtering capabilities in the detection circuit. For instance, for the bass drum not to open the snare drum's gate, we will EQ the low frequencies out on the snare drum's noise gate.
    A corrective possibility on lower quality toms with a decay that is too resonant (and too ugly) is to use a decay time that accelerates the natural decay of the tom's sound.

    Bass
    A way to use a gate with bass guitar is to synchronize it with the bass drum, which gets connected to the side chain input. If a bass note is played ahead of time, it will not be heard until the bass drum hit comes in, such that we will increase the feeling of "playing together", though the effect is quite radical and more appropriate for studio than for live sound.

    Gated reverb
    This is a classic setup, so much so that most reverb units feature it and it becomes not very practical to do it with a gate. The sound has a long reverb effect added to it; the reverb tail is then abruptly cut off with closing the gate very rapidly. For this effect a hold time of around half a second will be used. The effects is easier achieved by plugging the dry drum signal into the side chain input. Phil Collins made gated reverb very popular in its day.

    Keyboards
    Nowadays the range of sounds a keyboard or tone module can produce is enormous, so it is not possible to provide general settings. Use the general guidelines and criteria that have been explained on this tutorial.


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