the gate/expander in use

written by susiwong

A basic gate has a single parameter, the threshold – when the level is above the threshold the signal passes unchanged, when the level drops below the threshold the signal gets switched off, simple as that. Attack time ideally should be as fast as possible without causing clicks or distortion, so it’s preset to a sensible compromise with most gates, a few good gates even offer you a choice of two settings. Knee, hold and release determine shape and speed of the fade out, release is responsible for the overall decay time, knee changes the behaviour around the threshold level, helping you avoid the dreaded “motorboating” effect where the gate switches on and off rapidly. Think BSS or Drawmer gate vs Alesis compressor …

Hold simply specifies the “reaction time” from the moment the signal passes the threshold till the begin of the gain reduction – critical to preserve as much meat as possible from drums or keeping guitar decay intact. This is mostly what separates the good from the bad and the ugly. Last is the “range” or “floor” parameter, it sets a certain minimal volume to which the signal gets attenuated when dropping below the threshold, instead of being muted completely. Very helpful when you need to reduce the background noise between a singer’s phrases for example, much less obtrusive than muting the track completely. Set the floor so the background noise gets masked well enough by the music, often 3dB or 6dB are enough. This technique is also known as downward expansion, paired with a longer release and soft knee it’s often used for distorted guitars (with slow decay), too.

Some good gates offer sidechain filters allowing you to “zero in” on the important part of a complex signal, take a tom mic of a multi-miced drumset for example, where a lot of similar signals (bleed) are fighting for control. Difficult even with sidechain, impossible without. Worth noting that these filters do NOT influence your audio signal, only the signal used for detection, hence the name sidechain. And finally an external sidechain allows you to even borrow a signal from another channel to trigger your gate – the creative options are huge.Unfortunately not all hosts have this implemented in a user-friendly way. One popular example is tightening up the bass by triggering its gate from the kick.

A few things that work for me personally, ymmv:

• Vocals, sax etc.
  • As described above, expansion is the way to go, all you want to achieve is gently fading out the ambient noise without drawing extra attention to it.
  • You’ll reach a level where the noise is getting masked by the rest of the music.
  • Slow release, floor as high as possible, 3 or 6dB should be fine. Soft knee.
  • Of course there’s always the time-consuming method of manually editing out the noise, I like to do that on lead vocals, but quite often on background vocals or quick demos a gate is perfectly adequate.
  • All that said, there definitely are singers where muting the complete track might be a better solution. 😉
• Drums
  • Start with a gate, fast attack, use hold and release to shape the decay (the “boom” noise”) to taste.
  • When you start to “get there” you can try to experiment with the floor parameter for fine tuning.
  • Watch out, a big part of the sound might actually be on other channels (“bleed”), so solo your main track from time to time to get a feel for that.
  • If you need the gate to react e.g. to a single tom only, ignoring the prominent bleed from the neighbour drums, the sidechain is your friend. Use the HP/LP filters to single out a small frequency band unique to the tom in question, with a bit of experience and luck you often can isolate a tom pretty well. Granted, nobody said it would be easy …
  • Btw, the famous ’80s “gated drums” effect, pioneered by Phil Collins and others, doesn’t gate the drums themselves. Instead you have insane amounts of (plate) reverb on a send, often compressed, and you gate the reverb tail with a hard gate in time with the rhythm of the music. This gated reverb sound blends with the original sound to form an artificial, bigger than life new drum sound.
• Electric guitars
  • A mix of the above techniques, really.
  • Put the gate as early in your chain as possible, noise that isn’t there anymore can’t be amplified by the extreme compression of your OD/distortion devices …
  • Those OD/distortion thingies, especially in the digital domain, typically produce much less noise of their own than most people think, but they blow up every tiny bit of noise fed into them to monstrous proportions. Metal distortion is not funny … 😉
  • The problem is the decay of the notes. As long as you have kind of an “on-off” signal like in palm-muted heavy rhythm guitars you can deal with a lot of noise easily using a hard gate with fast timings.
  • Subtly decaying notes from a bluesy guitar and you might well be SOL …
  • Your best chance is to get as clean a signal as possible to start out with, PUs, shielding, cables, DI, tubes and biasing, switching off unneeded electrical devices, and finally your playing position (“turn to Mecca” – move around until you find a position minimizing EMI/RFI noise and STAY THERE !) – all make a big difference.
  • Then see what you can do with soft expansion as described above, or try manual editing.
  • Some folks swear by dedicated NR devices for guitar (Hush, Decimator, Denoiser etc) which combine an expander with a dynamic LP filter – very effective but somewhat tricky to handle and not available in software afaik.

All in all gating can be a big step towards a clean mix and I couldn’t live without it, but you have to know where to stop. I’ll take a noisy but natural signal over a chopped off, “over-gated” one every time. And as for all the creative applications of gating – experiment and write a cool article here … 😉