5 Ways to Use Audio Expansion to Enhance Your Drum Tracks

Many musicians and novice producers are aware of compressors, which decrease the dynamic range of an audio signal. But there are also dynamic processing devices called expanders that increase a signal’s dynamic range.

Below, we’ll share five tips for how to use expansion while mixing drums. But before we get to that, let’s quickly discuss the basics.

There are two types of audio expansion: upward expansion and downward expansion.

Upward expansion is often used to emphasize the peaks of an audio signal. This type of treatment increases dynamic range by amplifying the signal level that rises above a set threshold. Upward expansion is essentially advanced transient shaping. It’s great for enhancing the transients of sounds like drums, percussion, piano, guitars, lead synths, and vocals.

Downward expansion is useful for suppressing unwanted noise or instrument bleed. This type of treatment increases dynamic range by reducing the signal level that falls below a set threshold. The signal levels above the threshold will remain unaffected. Moreover, downward expansion functions much like a noise gate.

Expanders share similar controls as compressors like attack, release, threshold, and ratio. Most modern expander plugins also include a range control. Additionally, these controls function much like a compressor’s controls:

  • Threshold: Sets the level that triggers expansion.

  • Ratio: Sets the amount of expansion applied once the signal crosses the threshold.

  • Attack: Sets how fast expansion responds when a signal level exceeds the threshold level.

  • Release: Sets how fast the expansion recovers after a signal level exceeds the threshold level.

  • Range: Chooses between downward and upward expansion. It also limits the maximum amount of applied gain change.

Mixing Drums with Expansion

Expansion is a versatile tool that can tighten up kicks, bring out the snare while keeping hi-hats in check, or clean up decay and reverb tails to bring more space and pulse to your mix. Below, we'll take a look at five mixing techniques, with suggested settings for a number of common plugins. But you can, of course, use plugins you already own or prefer to replicate these settings once you understand the concepts.

Transient Enhancement

Upward expansion excels at adding punch and emphasizing transients to help individual drum sounds cut through the mix. For example, Waves Renaissance Compressor has an upward expansion mode that allows you to shape the frequency response of transients. This approach works great at tightening up kicks, snares, and toms while also giving them more snap. Use it to taste, but here are some suggestions to get you started:

  • Increase the Ratio to 0.5:1 or above.

  • Set fast Attack and Release times. Faster attack times accentuate transients more and shorter release times tighten up the sustain of sounds. Conversely, slower attack times and longer release times bring out more tone and body. This technique works much like a transient shaper except with more control over shaping the frequency response.

  • Increase the Threshold until your happy with the signal level response.

Alternatively, multiband dynamics plugins like Waves C4 and FabFilter's Pro-MB give you more precision and control. These versatile tools allow you to focus on precise frequency ranges that need enhancement. For example, you could compress a kick’s low-frequency band to give it a more consistent low-end while upward-expanding the mid band to bring out more punch.

Reducing Instrument Bleed

Downward expansion is useful for reducing noise or instrument bleed in recordings. It also works great at shaping the decay of drum recordings or completely removing various drum elements. This approach also creates more separation between notes or hits and tightens up the rhythmic feel. Furthermore, this type of expansion is similar to noise-gating.

The primary difference between a “gate" and an “expander" is the amount of level reduction that is applied. Typical noise gates abruptly cut off the sound when the signal drops below the threshold, whereas expanders are smoother—fading levels out instead of muting them. However, some noise gate plugins like FabFilter's Pro-G have expansion features.

FabFilter's Pro-MB multiband compressor is a rock-solid plugin capable of reducing instrument bleed and cleaning up drum recordings. To start, go ahead and try these settings:

  • Create a single band and set the process mode to Expand.

  • Decrease the Range knob and set a negative value to begin downward expansion. The signal level will start to attenuate as soon as it drops below the Threshold. The effect will also increase the dynamic range of the material.

  • For more controlled and precise results, set a harder Knee value so you can be more surgical with the Threshold.

  • Adjust the Attack and Release controls to taste. Faster attack times set how quickly the expansion responds while the release is used to control the tails of drum hits. For example, faster release times will significantly reduce the sustain of the drum hits.

  • Adjust the ratio as needed. Lower ratio values are more gentle and transparent sounding, while higher values give you more exaggerated results.

  • Optional: There is also an Expert tab that offers more advanced options to dial in your sounds further.

Targeting Drum Hits

Multiband dynamics plugins like Waves C6 are excellent at targeting and treating specific frequency ranges in drum loops or full mixes. For example, you may have a drum loop where you would like to emphasize the snare without affecting the hi-hats. In this scenario, single-band upward expansion would not work well because it will affect other drum elements in the loop.

However, multiband expansion will allow you create a band that isolates the snare. In Waves C6, for example, features six independent floating bands that work great at accentuating targeted sounds. Try these settings as a start:

  • Solo one of the bands.

  • Adjust the frequency and Q controls to isolate the appropriate frequency range.

  • Set fast attack and release times to give you more surgical precision.

  • Increase the Range control to taste. Range sets both the ratio and the maximum gain change.

  • Positive values also apply upward expansion.

  • Pull down the Threshold until your happy with the signal level response.

  • Adjust the Gain control as needed.

Restoring Dynamics

Upward expansion also works great at adding dynamic range back into poorly recorded drum tracks or over-compressed recordings. Using plugins like Waves C4, the company's older multiband compressor, you can apply upward expansion to restore punch to flat, over-processed recordings. Try these settings to start:

  • Load the Unprocessor preset.

  • Ensure all Range controls are set to positive values. Positive Range values apply upward expansion whenever the signal goes above the Threshold.

  • Adjust the Master Threshold for some reasonable expansion.

  • In most cases, the peaks and punch are mightily squashed in over compressed material. Faster attack times will help restore these peaks. Also, longer release times will help bring the presence and sustain back into the material.

Removing Reverb Tails

Downward expansion can also be deployed to reduce excessive reverb tails that cause clarity issues. In some cases, a gate will serve well at removing such reverb tails. However, there may be times where you want to tame them rather than completely remove them.

Downward expansion is a much gentler effect, cleaning up tails without totally removing the depth and character of the reverb. For example, this technique can work great at shaping the decay of a long reverb tail on a snare to make room for other drum elements.

Waves C1 features an Expander mode that works well at controlling reverb tails in drum recordings. Try these settings to start:

  • Switch the mode of the Gate/Exp module to Expander.

  • Set a negative noise floor value with the Floor control. The lowest value will chop the reverb tail off completely. Try starting around -15dB for a subtler effect.

  • Adjust the Attack and Release controls. Faster attack times set how quickly the expansion responds. Faster release times will significantly reduce the decay of the reverb tail.

  • Increase the Threshold until you begin reducing the reverb tail without affecting the tone and decay of the drum elements.

The methods outlined above are examples of various ways to use expansion to process your drums. However, these techniques can be used to treat the dynamic range of other sound sources as well.

In addition, these versatile tools can be used either for conventional sonic refinements or creatively to liven up your mixes. While not the most essential tool for every mix, expansion can be just the thing you need to inject some life into a track.

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