Definition
Ratio — A compressor parameter that determines how much gain reduction is applied to signal that exceeds the threshold, expressed as a proportion (such as 4:1) indicating how many decibels above the threshold are needed to produce one decibel of output above the threshold.
Ratio Explained
Ratio controls how aggressively a compressor acts on audio that exceeds the threshold level. At a ratio of 4:1, for every 4 dB the input signal goes above the threshold, only 1 dB passes through to the output. The remaining 3 dB are reduced. At 2:1, every 2 dB above the threshold becomes 1 dB of output. At 1:1, no compression occurs at all.
The ratio works in tandem with the threshold. The threshold sets where compression begins, and the ratio determines how much signal above that point gets reduced. Low ratios (2:1 to 3:1) provide gentle dynamic control. Medium ratios (4:1 to 6:1) offer noticeable compression suitable for most mixing scenarios. High ratios (8:1 to 20:1) approach limiting, where the signal is firmly held back from exceeding the threshold by more than a small amount.
At infinity:1, no signal passes above the threshold regardless of how loud the input becomes. This is pure limiting. Most dedicated limiter plugins operate at this ratio, creating a hard ceiling for the signal level.
How Producers Use It
For drum bus compression, a ratio of 4:1 is a solid starting point. This tames the dynamic peaks of kicks and snares while keeping the transients punchy. Combined with a medium attack that lets the initial transient through and a release that recovers before the next hit, this ratio glues the drum elements together without making them feel squashed or lifeless.
Bass and 808 compression benefits from higher ratios. A ratio of 6:1 to 8:1 on a bass channel keeps the level consistent so the bass stays present throughout the track without sudden dips or spikes. In genres where the bass must remain steady and upfront, like trap and R&B, tighter compression ratios prevent the bass from hiding behind other elements.
On the master bus, use low ratios (1.5:1 to 2.5:1) for gentle glue compression that binds the full mix together. High ratios on the master bus crush dynamics and cause pumping artifacts. The goal of master bus compression is cohesion, not gain reduction, so subtle ratios with conservative threshold settings produce the best results.
Parallel compression (blending a heavily compressed signal with the dry original) uses extreme ratios on the compressed channel, often 10:1 or higher. Because this heavily compressed signal is mixed underneath the uncompressed version, it adds density and sustain without removing the natural dynamics of the original performance.
Battle Tip: Use a 4:1 ratio on your drum bus to glue your kit together for battle playback. This ratio provides enough control to keep dynamics consistent without flattening the punch. Overly compressed drums (high ratios, low thresholds) lose their impact, while uncompressed drums jump unpredictably, both of which work against you in a competitive listening context.