Dynamics & Compression

What is Ratio & Threshold?

Threshold sets the level at which a compressor begins to act; ratio determines how aggressively the signal above the threshold is reduced.

How It Works

The threshold is the volume level (in dB) at which the compressor begins to compress. Any signal below the threshold passes through untouched; any signal above the threshold gets reduced according to the ratio. If the threshold is set at -20 dB, the compressor ignores everything quieter than -20 dB and only processes the peaks that exceed it. A low threshold means more of the signal gets compressed; a high threshold means only the loudest peaks are affected. The ratio describes the mathematical relationship between the input level above the threshold and the output level. At a 2:1 ratio, a signal that exceeds the threshold by 10 dB will only exceed it by 5 dB at the output — a 5 dB reduction. At 4:1, that same 10 dB excess becomes 2.5 dB at the output. At infinity:1 (limiting), nothing above the threshold gets through at all. Low ratios (1.5:1 to 3:1) provide gentle, transparent compression; high ratios (8:1 and above) produce aggressive compression approaching limiting. Threshold and ratio work as a team. A low threshold with a low ratio catches a wide dynamic range gently — great for leveling a vocal or tightening a bass. A high threshold with a high ratio only catches the loudest peaks but compresses them hard — great for controlling occasional transient spikes. Understanding this relationship lets you dial in exactly the right amount and character of compression for any source.

Why It Matters for Your Mix

Threshold and ratio are the two settings that determine whether a compressor is doing subtle, musical work or aggressive, obvious processing. Getting them wrong is the fastest way to ruin a track — too low a threshold with too high a ratio will crush the dynamics completely, while too high a threshold with too low a ratio may result in no audible compression at all. These settings also interact with the input gain coming into the compressor. A hotter signal hits the threshold more often and gets compressed more. This is why gain staging — having the right input level reaching each processor — is so important. Professionals think of threshold and ratio as a pair, adjusting one in response to changes in the other, rather than setting them independently.

Common Mistakes

Starting with extreme ratio settings

Beginners often crank the ratio to 10:1 or higher, thinking more compression is better. For most mixing applications (vocals, guitars, bass), a ratio of 2:1 to 4:1 provides musical, transparent compression. Reserve higher ratios for specific effects or limiting situations.

Setting the threshold too low

A threshold so low that the compressor is constantly reducing gain (never returning to 0 dB of gain reduction) means the compressor is working too hard. The gain reduction meter should move with the music — engaging on louder passages and releasing on quieter ones. If the needle is pinned, raise the threshold.

Not gain-staging before the compressor

If the signal hitting the compressor is too hot or too quiet, the threshold setting becomes meaningless — you are either compressing everything or nothing. Ensure your input level is in a healthy range (peaking around -12 to -6 dBFS) before setting your threshold.

How We Analyze This in Your Mix

RoastYourMix measures the peak-to-RMS ratio and the consistency of levels across your mix to infer how compression has been applied. Tracks with very consistent levels and low dynamic variation suggest low thresholds and/or high ratios. We also analyze the behavior of individual frequency bands to detect whether specific ranges are being compressed differently than others.

See Ratio & Threshold in Action

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faq

the quick answers.

What ratio should I use for vocals?+

For most vocal styles, a ratio of 2:1 to 4:1 works well. A softer singer with a wide dynamic range might benefit from 3:1 or 4:1 to keep the level consistent, while a more dynamically controlled singer might only need 2:1. Heavier styles (rap, rock vocals) might go up to 6:1 or 8:1 for a more controlled sound.

Is it better to use a low threshold with a low ratio or a high threshold with a high ratio?+

Both approaches can yield similar amounts of gain reduction but with different characters. A low threshold with a low ratio (gentle compression across a wide range) sounds smoother and more transparent. A high threshold with a high ratio (aggressive compression on peaks only) sounds more "grabbed" and controlled. For most mixing, the first approach is preferred.

What does the "knee" setting do?+

The knee determines how gradually the compressor transitions from no compression to the full ratio. A "hard knee" means the compression engages abruptly at the threshold — good for peak control and drums. A "soft knee" gradually introduces compression as the signal approaches the threshold, resulting in smoother, more transparent processing — good for vocals and bass.

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