Sidechain Compression EXPLAINED: 4 Fundamental Production Techniques
Are you taking advantage of sidechain compression in your productions? Here you’ll learn both the essentials and creative uses of this fundamental production technique in modern music.
By Charles Hoffman, Black Ghost Audio
Sidechain compression involves using a compressor’s sidechain input signal to trigger the device, rather than the compressor’s default input signal—this allows you to compress Track A, based on the signal level of Track B.
You can use sidechain compression in a subtle manner to provide clarity to different elements in your production, or in a more aggressive fashion to create substantial and creative pumping effects.
We’re going to take an in-depth look at some of the different ways you can apply sidechain compression to your mixes. These sidechain compression techniques will allow you to mix your low-end more effectively, add rhythmic pumping effects to instruments, blend vocals and guitars together in songs with a dense arrangement, and more.
1. Basic Sidechain Compression
Sidechain compression is perhaps used most commonly to provide clarity to the low-end of songs. A song’s bass will sometimes “mask” the song’s kick, causing the kick to sound less clear and defined. When the tonality of the bass sounds quite similar to the tonality of the kick, frequency masking is more likely to occur.
A kick that’s been soloed may sound big, round, and powerful:
But when layered with a bass, frequency masking occurs, and the kick can lose a lot of its desirable qualities. Listen to how much weaker the kick sounds in the following audio example compared to the previous example.
To fix this issue using sidechain compression, you can use a compressor like Waves’ C1 Compressor. First, apply the C1 Compressor to your bass track.
Set up the kick track as the C1 Compressor’s sidechain input signal—depending on the DAW you’re using, this is achieved in different ways. In Ableton, setting up a sidechain input signal is as easy as selecting a track from a plugin’s External Source dropdown menu.
Within the C1 Compressor, the settings you choose to use are of critical importance. I recommend starting with a ratio of 2:1, an attack time of 1 ms, and a release time of 30 ms. As you begin to reduce the threshold level, you’ll be able to hear the bass start to reduce in level every time a kick plays. If you have trouble hearing this effect, drastically reduce the threshold level, and you should be able to hear a very obvious “pumping” effect.
The goal is to reduce the threshold level to a point at which the kick recovers its lost desirable qualities, while the “pumping” effect imparted on the bass remains subtle. It’s somewhat of a balancing act.
However, you can certainly make use of this “pumping” effect creatively. When used in excess, the track that sidechain compression has been applied to will feel like it’s breathing, which can sound very cool.
The specific kick and bass you’re working with will heavily affect the compression settings you choose to use. For example, if your kick takes a long time to decay, you’ll likely need to use a longer release time within the C1 Compressor to prevent frequency masking.
To dial in your compressor settings appropriately, keep the following points in mind:
Attack: A fast attack time will reduce the level of the bass quickly when the sidechain input signal breaches the compressor’s threshold level. Faster attack times tend to provide enhanced clarity, while slower attack times will reduce clarity but provide a more natural sound. It’s really important that you rely on your ears to determine the attack time that sounds best.
Release: A fast release time will produce a short and concise “pumping” effect, while a long release time will produce a long “pumping” effect that swells over time.
Ratio: Using a gentle ratio (2:1) will provide a less intense “pumping” effect when the sidechain input signal breaches the threshold level, while a heavy ratio (10:1) will provide a more intense “pumping” effect.
Threshold: It’s sometimes difficult to dial in the attack and release values when you’re applying a light form of sidechain compression because their effects may not appear obvious. To overcome this issue, you can significantly reduce the threshold level so that the compression being applied is more intense and noticeable. Dial-in the compressor’s attack and release settings and then bring the threshold level back up to reduce the intensity of the effect being applied.
2. The Ghost Trigger Effect
Sidechain compression can be used to add rhythmic pumping effects to instruments using a ghost trigger. A ghost trigger is typically a kick, snare or other percussive sound placed on a track that’s been muted. The track is routed pre-mixer into a compressor’s sidechain input.
In Ableton, you’ll want to tap the ghost trigger track “Post FX.” Tapping the ghost trigger track “Post Mixer” won’t have the desired effect because once the signal reaches Ableton’s Mixer section, it will be muted. Within the C1 Compressor’s External Source dropdown menu, select your ghost trigger track, and then within the External Tapping Point dropdown menu, select “Post FX.”
Take a listen to the following audio example containing a pad, and then listen to the rhythmic pumping effect that’s been applied using the C1 Compressor and a ghost trigger.
If you layer some drums with the unprocessed pad, the pad sounds quite boring in comparison.
With the rhythmic sidechain compression effect applied to the pad, it helps glue everything together by providing the pad with some rhythm.
In the following image, the ghost trigger is the green track, the pad is the blue track, and the drumbeat is the yellow track. The C1 Compressor has been applied to the pad, using the ghost trigger as the sidechain input signal, tapped “Post FX.”
Flume and other similar artists make heavy use of rhythmic pumping effects within their music. In “Sleepless feat. Jezzabell Doran” by Flume, you can hear a rhythmic pumping effect applied to the repetitive lead vocal sample that’s been pitched upward.
We looked at a basic four-to-the-floor ghost trigger rhythm in our example, but feel free to create more complex ghost trigger rhythms. Dropping a complete drum break onto your ghost trigger track can deliver interesting results and spice up dull and static sounds. You may even choose to subtly trigger your entire song with a 4/4 kick trigger, providing a continuous but non-intrusive pulse to the song.
3. Multiband Sidechain Compression
Multiband sidechain compression comes in handy when you only want to compress a certain frequency range—the results tend to sound more transparent than when you apply sidechain compression using a broadband compressor. You’re able to significantly reduce noticeable pumping effects while still providing clarity to your songs.
For example, multiband sidechain compression makes it possible to selectively compress the midrange of a guitar bus in response to the level of a vocal track. Vocal intelligibility lives with-in the 1-5 kHz range, which sometimes gets masked by guitars. When making use of a dense arrangement in which there’s not a lot of space for both the vocals and guitar, multiband sidechain compression is a great solution.
Compressing the low-end of your guitars might be undesirable since it can cause them to lose their warmth, while compressing the top-end might be unnecessary since there tends to be more space for various track elements the further you move up the frequency spectrum.
A compressor like Waves’ C6 Multiband Compressor can be used to apply multiband sidechain compression to a track. Drop an instance of the C6 Compressor onto the track you’d like to compress. If you want to compress the midrange of a guitar buss to make room for vocals, apply the C6 compressor to the guitar bus. Make sure that you select the “C6-SideChain” component from your plugin folder, as opposed to the “C6” component. One provides sidechain functionality, whereas the other does not.
Select the vocal track as the C6 Multiband Compressor’s External Source, and then open the plugin.
Bypass the low band, the low-mid band and the high band while leaving the mid-high band unaffected. Set the mid crossover frequency to 1,000 Hz and the High crossover frequency to 5,000 Hz. When compression is applied, it will selectively affect frequency content between 1,000-5,000 Hz.
Toggle the active band from Internal mode to External mode—this will cause the band to respond to the External Source you’ve set up.
Using a negative Range value will cause the band you’re manipulating to behave as a compressor. Positive values cause the band to operate as an expander. The Range acts as a ratio control, as well as a way to control the maximum gain reduction each band is capable of applying. If you want to use a higher ratio, decrease the Range value.
Increasing the amount of compression applied can be achieved by reducing the Threshold level of a band. Since multiband sidechain compression is often used to deliver transparent results, you’ll likely want to avoid using a heavy hand when dialing in the Range and Threshold levels. At this point, knowing how this compressor works, you should dial in the active band’s attack and release settings.
4. Reverse Sidechain Compression
When you apply broadband sidechain compression to a track, you affect its volume envelope. By committing the processing you’ve applied to audio, you can do creative things like reverse the volume envelope of the clip.
In some DAWs, you need to route the output of the affected track to the input of a blank audio track and then resample the audio. Within Ableton, this process is streamlined since you can “Freeze” and “Flatten” tracks offline.
Let’s take a look at how to do this using the pad from the rhythmic pumping effects section of this guide. In the following example, rhythmic sidechain compression has already been applied to the pad, but it hasn’t been committed to audio yet. As a result, you’re able to hear the effects of sidechain compression but not visualize them within the audio clip’s waveform.
This is the same audio file used previously:
Before you reverse the audio clip, you need to commit the sidechain processing you’ve applied to audio. Otherwise, the audio clip will get reversed, but the effects of the sidechain compression will not.
Right-click on the name of the track that sidechain processing has been applied to, and select “Freeze” from the dropdown menu.
Then, right-click on the track’s name again and select “Flatten.”
As you can see, the effects of sidechain compression have been committed to audio.
By reversing the clip in Ableton’s Clip View window, the chord progression is reversed, and consequently, so is the volume envelope. What previously sounded like a series of risers has taken on the volume envelope of a series of plucks.
You might find that reversing the audio clip makes the groove of your arrangement feel forced. Try pushing the clip backward in time by an eighth note to create a syncopated rhythm.
Conclusion
Many productions can benefit from sidechain compression, meaning that as a producer, it’s helpful to understand how sidechain compression works. Wrapping your head around the concept of sidechain compression is the first step of the learning process, while the next step is to put the techniques mentioned throughout this article into practice. You can demo all of the compressor plugins mentioned in this guide for free, so there’s nothing standing in your way.
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