Noise Gates: Gates: Not Just for Noise Anymore

Audio gates are one of the most powerful, yet often overlooked, tools in your recording arsenal. A properly set gate can tighten your drum tracks, clean up your vocals, reduce leakage from other sound sources, minimize noise from amplifiers or cassette tapes, or create dramatic effects.

Many of you may only be familiar with the gate section of your compressor. While these can be useful, they are very limited. Usually you're stuck with nothing more than a threshold control. This means that the gate functions as an on/off switch, allowing signals over threshold to pass while muting everything below. Such a device is really only useful for percussive sounds. You can make good use of your compressor's gates for kick or snare drum by setting the threshold to pass the attack while cutting out as much of the decay as you desire. You can also use the gated signal to provide a tight trigger signal for a sampler. However, with other instruments you might end up cutting out desirable portions of the note with little, or no, positive effect. Dedicated gates provide more control, making them useful for a wide variety of audio tasks.

All gates have a Threshold control. As with a compressor, the Threshold setting determines when the gate goes to work. But with a gate, Threshold is the level at which the gate begins to turn off the signal. With a simple gate, anything below threshold will be cut off while anything above will pass unchanged. Pretty simple: You set the Threshold where the music you want gets through and the noise goes away. But, what happens with a long sustained note? You've all heard it: Ahhh.....uhh......uh.....u. That's where the Release (or Decay) control comes to the rescue. On a gate, Release controls how quickly the signal level falls after it goes below threshold. Release settings are stated in time per 20 dB of attenuation. Long settings will allow more of the note's decay to get through. Short release times make the gate perform just like the ones in your compressor. Some gates even provide a choice of slope for the release function, where you can choose between linear or logarithmic attenuation slopes.

Hold (or Delay) is another setting which controls the onset of gating. The Hold function delays the start of attenuation for a set period of time. If the input goes above threshold again during the Hold period, no attenuation occurs, and the Hold time is reset to begin again when the level falls. This is very handy for use on vocal tracks where sustained levels might vary around the threshold. Turn up the Hold setting to prevent long sustained notes from being cut off. Hold settings of about 0.5 second can also work well when dubbing from a noisy cassette tape, allowing the last note to die while eliminating tape noise between songs.

Attack controls how quickly the gate "opens", returns to unity gain, once the signal exceeds threshold. Fast settings are useful for percussive sounds, but can result in an audible click as the circuit turns on. You can usually hear a bit of this with the gates on your compressor. The Attack setting requires some experimentation: Too fast and you hear that click — too slow and you'll lose the initial transient. Really slow Attack settings result in a pseudo "backwards tape" effect as the gate doesn't open until the note's attack is over.

Depth (or Range or Floor) determines how much attenuation is applied to the signal when the gate is active. Most gates offer a maximum attenuation of 80 to 90 dB, effectively cutting off the signal completely. Lower Depth settings can help to reduce audible pumping. Sometimes completely removing the noise sounds worse than no gating at all. In these cases you might wish to adjust the Depth setting in order to sound more natural by retaining some of the ambience. The Depth control is also used when performing dynamic expansion, more on this later.

Many gates have a Key (or Sidechain or Insert) input allowing direct access to the control circuit. A common use for the Key input is to prevent false triggering of the gate. When you're gating a kick drum, you don't want the gate to open every time it "hears" the snare. By equalizing the Key signal to only respond to low frequencies, the gate will only open when the kick drum is struck. That means your "kick" track will produce only kick drum during mixdown. Many newer models have side-chain EQ/Filter built in for just this purpose. That sure saves time and patch cords.

Gates are also used to expand dynamic range. Basically you set the threshold in the lower middle of your current dynamic range then experiment with Release times and Depth settings until you increase the dynamic range by further reducing the lowest levels. To really do a proper job, expander/gates provide a Ratio control to aid expansion. The Ratio on a gate is reversed from that of a compressor: ratio settings usually range from 1:1.1 to 1:100. This Ratio setting determines how much expansion will take place. At the extreme setting of 1:100, the unit acts as a noise gate: a level of -1 dB is dropped to -99 dB (or the Depth setting, whichever is higher). However, with a moderate 1:3 ratio every decibel below threshold is expanded to -3 dB. When using an expander, set the threshold to where only the loudest sections reach threshold. This is known as Downward Expansion. Moderate attack settings will produce the best results for expansion.

We already mentioned using gates to control elements of a drum kit, essentially isolating kick, snare and tom sounds from one another. But does this sound too sterile and '80s? Try multing a signal off your tape return on the snare track. Run that to a gate and set it really tight. Then bring it back into the mix under the non-gated snare track (and check phase to be safe). This signal can add clarity and punch to the existing snare track without sounding artificial. You can also try EQ'ing this signal to be brighter, adding crispness without adding hi-hat or other bleed.

With so many controls available, these gates must also be able to make some cool effects. We already mentioned the retro backward effect created by very slow Attack times. Experiment with this on varioussources and you can create automatic volume-pedal swells with guitar, throbbing bass lines, or that '80s snare sound. Another neat trick is to use a gate to create a "kick drum" from a low-frequency oscillator. To accomplish this, feed an oscillator tuned to around 80 Hz (or lower) to the audio input and trigger the Key input with the real thing (or any other impulse). Shape the audio with fast Attack and other settings similar to what you use for kick drum. This "kick" works great for techno tracks, or it can be mixed with the real thing for that heavy metal hyper drum sound. Or put a long hold on it for a hip-hop "boom" sound. You can use a similar setup to lend a rhythmic feel to any steady element. Use a shallow Depth setting, maybe -3 dB, then feed something like a sustained string or organ sound to the audio input while triggering the gate with the kick drum. You'll add a subtle throbbing rhythm to your pads. Take this same idea and trigger organ chords from a click track, or manually create a new "click track" just to turn elements on and off in the mix.

One subtle dynamic effect is to place a gate between an auxiliary send and an effect input. You can set up a system where only louder vocals receive reverb or echo, creating a feeling that the singer is "belting it out". See David Bowie's "Heroes" for an example of this, though in that case distant room mics were used for actual reverb. Adding gates after effects can help clean up noisy spring and digital reverbs — try keying them from the effect input and add a long hold that's appropriate to the song. But you can also abuse this trick and cut off all the tails of a reverb so that the effect is "hidden" under the main track. This creates an odd environment where vocals seem dry yet shimmery. A nice sonic trick.

As you can see, the creative uses for gates are only limited by your imagination. The only "rule" I follow is to only use gates for mixing. If I screw up the settings during tracking, I'm stuck with the results!

Drawmer - Powergate DS501 gate

The Drawmer 201 gate has long been a studio staple as a versatile, easy to use gate, with all the standard features and a quick responsiveness to fast transients. With their new gate, the 501, even more has been added to the 201's arsenal. "Peak Punch" is the main feature, a section that can be switched in to add a 10 ms boost at the opening of the gate. The amount of boost can be varied, up to 10 dBs, and a narrow EQ can be applied to the boosted signal, from 75 Hz to 16 kHz, but the 10 ms time is set in stone. What does this effect do? It can seemingly restore attack to a gated percussion sound, and also create new transients from the source if so desired. In use I was able to clear up murky snare and kick sounds on tracks I was mixing, especially when blending back under the original signal. Too much EQ or boost can sound unnatural, so be careful, and sometimes the sound created by this can feel dry and electronic, right on the edge of the speaker and not quite sitting in the mix with the actual drum sounds. Proper placement and usage is important, but what an amazing tool. Also new to the 501 is a 4 segment LED meter to show input levels, making setting threshold easier than ever. The 501 is one of my little tricks now, following me around when I freelance, and is opening up more sounds for me and helping revive dead drum sounds on occasion.