However, this is not the only approach to compression. Instead of squashing things down when they go above the threshold, we can instead boost the signal below the threshold.
Enter upwards compression!
Upwards Vs Downwards Compression, What’s The Difference?
With compression, we know that the threshold is a very important setting that determines the overall character of the effect.
The fundamental difference between upwards compression and downwards compression lies in how the signal is treated when it is either below or above the threshold.
Downwards compression only affects the signal once its level exceeds the threshold, while upwards compression treats the signal only while it is below the threshold – by boosting it! To people who are only familiar with downwards compression, upwards compression may seem like a radically different approach, but it’s equally valid in terms of actually compressing the signal.
So with upwards compression, instead of the loud parts becoming softer, the soft parts become louder, and the dynamic range is reduced similarly to downwards compression. However, these two effects ultimately sound different and have different uses, benefits, and drawbacks.
Downward compression works by “clamping down” on anything past the threshold, evening out the overall level of a signal by making the louder parts closer in volume to the softer parts.
With downward compression, the ratio sets how much to compress once the signal passes the threshold.
We set our ratio using an x:1 setting. This means for the output sound to be 1 dB over the threshold, it needs to be x dB over the threshold going into the compressor.
For example, if we use a 4:1 compression ratio and our signal crosses the threshold by 4 dB, we will hear a 3 dB decrease in volume. Using the same settings, if a signal went 8 dB over the threshold, it would be reduced by 6 dB.
Upwards compression raises the amplitude of everything in the audio signal below the set threshold, while keeping everything above that the same or relatively unaffected (according to the knee).
This can be useful in applications where you can hear the louder parts of a recording just fine, but can’t pick out the softer sections as well.
For example, a live recording of a band might have sections where the energy dies down a little too much, but most of the time the volume is just fine. The compressor is constantly engaged if you use downwards compression to level out this recording. However, with upwards compression, the compressor only kicks in when it is really needed.
Where upwards compression really shines, in my opinion, is it brings out certain undertones that would otherwise go unnoticed. We’ll talk about some practical applications in a bit, but upwards compression is a great textural enhancer when it’s forcing things into the foreground.
There are not too many plugins explicitly labelled as upwards compressors. Instead, you’ll probably find upwards compression as a mode in a compressor plugin, or under the hood as a secret ingredient in a “one-knob” enhancement plugin.
When talking about multiband upwards compression, you’re getting into OTT territory.
OTT is a type of multiband compression effect that aggressively levels out three or more separate frequency bands (eg. bass, mids, highs). Each band is effectively squashed into a solid tube of sound, but the result is much cleaner than distortion.
OTT compression uses both downwards and upwards compression to achieve this, but it’s fair to say that upwards compression is the key ingredient.
Compression is not just a utility or a problem solver. It can be used in a bunch of cool and interesting ways for sound design, and this is where you can really let loose with some unusual compression settings.
As mentioned, upwards compression has the noticeable effect of boosting sounds that are so soft they are often missed. So right away, we can see the sound design potential here.
For starters, you could apply aggressive upwards compression to a field recording and uncover all sorts of hidden details. I suggest using multiband upwards compression for this because field recordings have a wide frequency range, typically covering the entire spectrum of human hearing.
I’m also a big fan of using upwards compression after reverb, as it greatly exaggerates the decay time to create “larger than life” reverberation effects. This trick works really well on lead synths, vocals, or anything that you want to stand out in a track.
When it comes to downwards compression, the results are less attention-grabbing as you are dealing with an overall reduction in gain when it comes to the actual effect.
If this is a problem for you, you have my permission to reach for the makeup gain. Normally I’d be careful with this control when using compression as a mixing tool, but for sound design purposes it matters less.
When using downwards compression for sound design, try out settings you wouldn’t normally use and listen to how the compressor reacts differently compared to “correct” usage.
For example, you can very often set the attack and release times to the smallest possible settings to apply distortion to the signal. It’s not always the nicest distortion tone depending on the compressor, but try it out on bass and drums as an alternative to fuzz or overdrive.
Usually when we use compression, we still want to preserve the overall dynamics of whatever we are using it on. But when it comes to using compression for sound design, I would instead encourage you to explore using it to completely alter the dynamic profile of the original sound.
This is also where sidechain compression comes in handy, because it allows you to map the dynamics from one sound onto another. This means sidechain compression has more uses than just making your track pump whenever the kick hits.
While upward compression and downward compression are both different types of the same effect, the two methods are completely different beasts that are best suited for different uses.
Downwards compression treats the signal only when it goes above the threshold, by reducing the volume or “pushing it down.” On the other hand, upwards compression only affects audio signals below the threshold, by increasing the volume and pushing everything up.
The overall effect is roughly the same – the signal is compressed and the dynamic range is reduced. But the difference in how the compressor actually treats the signal ultimately results in two distinctive effects.
Of course, it may not be an either-or situation. In the same way your effect chain might use multiple compressors performing different amounts of gain reduction, upwards compression and downwards compression can be used together to give you even more control over dynamics.