What Is Upward Dynamic Range Compression In Audio?


While studying dynamic range compression on its own or looking for experimental audio processing techniques, you may have come across the term “upward compression”.

What is upward compression? Upward compression is a type of dynamic range compression that boosts the amplitude of an audio signal below a certain threshold while maintaining the amplitude above the threshold. Upward compression is available in digital plugins and via parallel compression with hardware or software.

In this article, we’ll take a closer look at upward compression to better understand the process and how it can be used to our benefit (or dismay).


A Brief Discussion Of Dynamic Range Compression

Before we get to the specifics of upward compression, let’s get a general understanding of dynamic range compression as a whole.

What is dynamic range compression? Dynamic range compression is the process of reducing the dynamic range of an audio signal (the difference in amplitude between the highest and lowest points). Compression does so by attenuating the signal amplitude above a set threshold point.

Typical compressors will effectively attenuate the output of the loudest parts of a signal while allowing the quieter parts to pass at full volume. This effectively compresses/reduces the dynamic range of the signal passing through the compressor.

The difference between these “loud” and “quiet” parts is dependent on if the signal is above or below a set threshold amplitude, respectively. When the signal is “loud”, the compressor attenuates it by a set ratio, and when the signal is “quiet”, the compressor outputs it without any attenuation.

However, as we’ve touched on briefly, this is not the case with upward compression. We’ll get to that in a moment.

Compression has a wide variety of applications in audio mixing/production. These applications include, but are not limited to, the following:

  • Maintaining a more consistent level across the entirety of the audio signal/track
  • Preventing overloading/clipping
  • Sidechaining elements together
  • Enhancing sustain
  • Enhancing transients
  • Adding “movement” to a signal
  • Adding depth to a mix
  • Uncovering nuanced information in an audio signal
  • De-essing
  • “Gluing” a mix together (making it more cohesive)

To learn more about audio dynamic range compression as a whole, check out my in-depth article The Complete Guide To Audio Compression & Compressors.


What Is Upward Compression?

So “downward” compression attenuates a signal above a set threshold to reduce dynamic range. Upward compression reduces the dynamic range in a different way: by amplifying the signal below a set threshold and not affecting any signal above this set threshold.

By increasing the volume of the “quiet” parts and keeping the “loud” parts the same volume, upward compression effectively compresses the signal’s dynamic range.

Both compression styles ultimately reduce the dynamic range, but upward compression uses amplification while normal compression utilizes attenuation.

Let’s consider some visual graphs to aid in our understanding of upward compression.

A “downward” compressor with a 2:1 ratio would have an input/output graph like this:

We can see clearly that, above the threshold, the output is attenuated versus the input. The 2:1 ratio example means that for every 2 dB that the input signal exceeds the threshold, the output signal will only be 1 dB above the threshold.

For more information on compressor ratio and threshold settings, check out the following My New Microphone articles:
Dynamic Range Compression: What Is The Ratio Control?
Dynamic Range Compression: What Is The Threshold Control?

An upward compressor with a 0.5:1 ratio (0.5 is the reciprocal of 2) would have an input/output graph like this:

We can see that the output level is greater than the input level below the threshold. In this example, for every 1 dB the input signal level drops below the threshold, the output will only drop 0.5 dB.

Because upward compression does not attenuate the loud parts, it may sound more natural (less “squashing”) than typical compression. However, pumping, increased noise floor and other non-ideal results can potentially arise when using upward compression.

The FabFilter Pro-C 2 (link to check the price at Plugin Boutique) is an audio compressor plugin that has a superb option for upward compression.

FabFilter Pro-C 2

FabFilter is featured in My New Microphone’s Top Best Audio Plugin (VST/AU/AAX) Brands In The World.

Upward compression is used to achieve many of the same results as “downward” compression, only in a slightly different way.

The major difference is that upward compression doesn’t attenuate peaks. This, of course, makes the “loud” parts of a signal sound more natural. However, it does restrict the use of upward compression when it comes to taming transients, adjusting peaks, reducing the potential for overloading, de-essing applications.

That being said, upward compression works very well in achieving the following:

  • Maintaining a more consistent level across the entirety of the audio signal/track
  • Enhancing sustain
  • Adding “movement” to a signal
  • Adding depth to a mix
  • Uncovering nuanced information in an audio signal

Needless to say, upward compression is nowhere near as popular as “downward” compression but can certainly be used as another tool in the audio engineer’s toolbox.

To recap, let’s consider the following points:

  • Downward compression attenuates the audio signal above a set threshold by a set ratio in order to reduce dynamic range.
  • Upward compression amplifies the audio signal below a set threshold by a set ratio in order to reduce dynamic range.

A Note On Parallel Compression

We don’t need a designated upward compression plugin to produce the effect of upward compression. We can get something very similar with parallel compression.

Parallel compression is a parallel processing technique that effectively duplicates an audio track and passes one of the copies without processing and the other through a compressor.

Parallel compression (sometimes referred to as “New York” or “Manhattan” compressions) can be applied to single tracks, busses, or any other tracks within a mix.

By bringing up the volume of the compressed track “copy”, assuming perfect phase cohesion, we can pseudo-amplify the original track.

For levels below the threshold of the compressed track, any increase in the compressed signal’s volume will be at a 1:1 ratio to the overall level of the combined tracks.

For levels above the threshold of the compressed track, any increase in the compressed signal’s volume will be at a ratio less than 1:1 to the overall level of the combined tracks.

In this case, we don’t have perfect unity above the threshold like we would with a standalone upward compressor. However, we do have a situation where the combined output levels below the threshold (of the compressed copy) are boosted more than the levels above the threshold (of the compressed copy).

Also, by adjusting the volume of the compressed copy, we affect the levels (of the combined output) below the threshold more so than the levels above the threshold.

Parallel compression is a fairly common technique and can achieve very similar results to upward compressors (though they are not 100% identical).


Upward Compression Vs. Expansion

Throughout this article, I’ve avoided stating that “upward compression is the opposite of downward compression”. Though there is some truth to that statement, there is also truth to the statement “dynamic range expansion is the opposite of dynamic range compression”.

So if both these statements can be considered true, then what are the differences between upward compression and expansion?

Well, as we’ve discussed, upward compression brings the audio signal below a set threshold up in level by a set ratio to compress the dynamic range. On the other hand, expansion brings the audio signal below a set threshold down in level by a set ratio to expand the dynamic range.

So while both processes affect signal levels below a set threshold (as opposed to above the threshold, like with standard downward compression), they affect the signal differently within this dynamic range. Again, upward compressors boost the output amplitude below the threshold while expanders drop the output amplitude below the threshold.

In the image below, I’ve made an easy comparison between a [downward] compressor, upward compressor and expander to help you visualize. As per usual, the input level is plotted along the x-axis, and the output level is plotted against the y-axis:

And with that, I hope you’ve learned what upward compression is and how it’s used in the context of audio mixing and production.


What are the different types of audio compressors? The term “type” can have a few meanings so let’s look at a few different “types of compressors.

In terms of circuit topology, compressors will generally fall into one of the following types:

In terms of how a compressor will perform when compressing an audio signal (and the typical tasks it will be set to do), we can think of the following types of compression:

What is audio data compression? Audio data compression is the process of encoding digital audio information into fewer bits than the original signal/file, thereby compressing/reducing the file size. Data compression can be either lossless (eliminating redundant info) or lossy (eliminating unnecessary or “less-important” info).

Popular lossless audio compression formats include:

  • FLAC (Free Lossless Audio Codec)
  • ALAC (Apple Lossless Audio Codec)
  • APE (Monkey’s Audio)
  • OFR (OptimFROG)
  • WV (WavPak)
  • TTA (True Audio)
  • WMAL (Windows Media Audio Lossless)
  • Dolby TrueHD
  • MLP (Meridian Lossless Packing)
  • MPEG-4 ALS (Audio Lossless Coding)
  • MPEG-4 SLS (Scalable Lossless Coding)
  • RealAudio Lossless

Popular lossy audio compression formats include:

  • Dolby Digital
  • Dolby Digital Plus
  • DTS Coherent
  • MPEG-1
  • MPEG-2
  • MPEG-4
  • MPEG-H
  • Vorbis
  • WMA (Windows Media Audio)

Determining the best compressor for your audio needs takes time, knowledge and effort. For this reason, I’ve created My New Microphone’s Comprehensive Compressor Buyer’s Guide. Check it out for help in determining your next dynamic range compressor purchases.


This article has been approved in accordance with the My New Microphone Editorial Policy.

Arthur

Arthur is the owner of Fox Media Tech and author of My New Microphone. He's an audio engineer by trade and works on contract in his home country of Canada. When not blogging on MNM, he's likely hiking outdoors and blogging at Hikers' Movement (hikersmovement.com) or composing music for media. Check out his Pond5 and AudioJungle accounts.

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