Gates & Expanders: The Good and the Bad
Gates and Expanders are a type of dynamics processing used to reduce unwanted noise in audio recordings. They operate like compressors, except that instead of attenuating signals as they pass a threshold (as a compressor would), gates and expanders attenuate signals below a user-defined threshold. They’re popular for use in radio, podcasts, television, film, live sound, and anything where vocals and noise are commonplace. Most expanders include additional controls for decay, threshold, and ratio, as well as side-chain filters. These additional controls greatly help to control how abruptly the expander attenuates sound, as well as the sensitivity to sound as it passes through the expander. In this post, we won’t delve into how to operate expanders, but instead, focus on the potential advantages and drawbacks of using one.
Expanders Vs. Gates
Expanders are an all-encompassing term, such that all gates are expanders, but not all expanders are gates. Gates are simply expanders that provide extreme output attenuation for signals that drop below the user-defined threshold. Gates act more like an on-off switch, whereas expanders offer some flexibility as to the degree to which output signals are attenuated. Colloquially, expanders are conflated with gates even though they’re not technically the same. The same limitations of expanders apply to gates as well.
Expanders are simple algorithms with binary logic. If the signal level falls below the detector threshold, the expander attenuates the output signal. If the signal level exceeds the detector threshold, then the expander allows the signal to pass through to the output, unaffected. Time controls simply delay the onset of the expander or allow for more gradual attenuation, but the basic logic of the expander remains the same. As a result, expanders tend to work very crudely, and rarely strike a good balance between subtlety and noise reduction for vocal recording. The end results typically come across as abrupt and displeasing, even though they successfully reduce noise in a technical sense.
Expanders for Vocal Recordings
For vocal recording, expanders work incredibly well at reducing ambient noises – in fact, they work too well. Expanders tend to sound very abrupt and unnatural, allowing the signal to pass through suddenly, then cutting off quickly. Our ears prefer to hear consistent noise, however distracting, rather than abrupt transitions between no noise and sudden noise.
Setting the Threshold
Expanders often allow for user-defined thresholds that can be custom set for the program material in your recording. Unfortunately, most vocal recordings contain dynamics with varying levels in speech. You may set an appropriate threshold to allow the signal to pass through the expander unaffected for the majority of the recording, but if the person drops to a low speaking voice or whispers (without moving closer to the microphone), then the threshold will need to be adjusted. This can be especially difficult for a recording with a noisy background. For a long recording of twenty minutes or more, the threshold will need to be adjusted numerous times using software automation. With the amount attention needed, you might as well edit out the silences by hand or simply leave the noisy as-is. If the person speaks and does not exceed the threshold, then important words may not be heard. For video, this can be especially jarring as you may see lips move without hearing any sound. We don’t recommend using expanders for general vocal recordings for this reason.
When to Use Them
Oddly enough, expanders work quite well for recordings with low noise floors, to begin with. A pristine, studio-quality recording in an isolated environment sounds just fine with an expander. The results are so good, that the differences between the expanded recording and raw recording will be virtually indistinguishable from one another. Likewise, expanders sound great on someone addressing a microphone with precise, consistent microphone technique, who addresses the microphone closely, clearly, and loudly for each word. For someone with this much attention to detail, it’s unlikely that you’ll have noise issues in the first place.
For music recording, expanders work incredibly well for instruments with fast transients. Things like kick drums, floor and rack toms, congas drums, and bongos all benefit from expanders, even in studio environments. These instruments all generate sound with fast, sudden onsets and rapid falloff, making them perfect for the naturally abrupt transitions that expanders offer.
Expanders make excellent tools for reducing ambient noise levels, but their natural abruptness makes them poorly suited for use on vocal recordings. More often than not, it’s simpler and easier to edit out or attenuate silences by hand rather than rely on the crude binary logic of an expander. Using gates on clean vocals recording in a studio or with excellent microphone technique rarely benefit from expanders, and the threshold setting may actually cut off the beginnings of words. For those of you doing music recording, use expanders on floor toms, rack toms, kick drums, congas, and bongos, but they’re best avoided for vocal recordings.
People commonly look to expanders as a tool to clean up noise in a vocal recording, but expanders aren’t well suited for the job. There are surprisingly very few things you can do to remove noise from a recording in post-production, hence why we’re staunch advocates for practicing the techniques that create great recordings, to begin with. Refer back to our vocal recording basics series for information about how to create great recordings right out from the start.
What were your experiences using expanders and gates for vocal recording? Let us know in the comments below.