Compression is one of the most powerful tools in your audio toolkit, it is also the most misunderstood. Today we’re going to talk about these three compression parameters: threshold, ratio, and knee. Understanding how these interact will give you precise control over how your compressor shapes dynamics, whether you’re mixing, mastering, or sound designing.
Threshold: When Compression Begins
The threshold is the level at which your compressor starts working. Any signal above this point will be reduced in gain based on the ratio you’ve set. Set a lower threshold if you want compression happening more often, affecting more of the signal. Put it higher if you want to only shave off some peaks.
Think of threshold as the gatekeeper. It decides what gets compressed and what doesn’t. In mastering, you’ll often keep the threshold high so that only the loudest moments trigger compression. In mixing, lowering it lets you keep a vocal or instrument more consistently controlled.
Ratio: How Much Compression Happens
Once the threshold is crossed, the ratio determines how strong the compression is. A ratio of 2:1 means for every 2 dB above the threshold, only 1 dB makes it through. A 4:1 ratio means for every 4 dB above the threshold, just 1 gets through.
Low ratios (1.2:1 – 2:1): Gentle, transparent control, often used in mastering.
Moderate ratios (3:1 – 5:1): Useful for vocals, bass, guitars—firm but musical.
High ratios (10:1+): Limiting territory—brick-wall control for peaks.
Ratio is essentially the strength of your compressor’s grip.
Knee: How Compression Feels
The knee controls how abruptly or smoothly the compressor engages when the threshold is crossed.
A hard knee means the compressor kicks in instantly once the threshold is exceeded. This creates a sharper, more aggressive sound, which is great for drums or aggressive mixes.
A soft knee gradually applies compression as the signal approaches the threshold, resulting in a smoother, more natural response, which is perfect for vocals, acoustic instruments, and mastering.
Think of the knee as the personality of the compressor: is it strict and immediate, or gentle and forgiving?
Bringing It Together
Threshold sets the point of action, ratio decides how forceful the action is, and knee determines the character of that action. Together, these three parameters define whether your compressor is subtly massaging dynamics or aggressively reshaping them. Combine this with what we’ve learned in the Article about Attack & Release and you’ll be well on your way to become a master at Compression!
Practical tip: When dialing in compression, always listen first: is your track smooth or spiky, balanced or unruly? Let the material guide your choices, and remember that compression isn’t just about control, it’s about shaping feel and musicality.
Want to learn more about compression? Join us Thursday, September 25th, at 10:00am ET (4:00pm CEST) for demonstrations teaching you expert-level compression techniques during the educational launch event of our first ever plugin.
Until next time,
Rob
