Ratio and Threshold in Compression: Setting Levels

Threshold and ratio work together to determine how much compression occurs. Threshold sets where compression begins while ratio sets how aggressively the compressor reduces gain above that point. Understanding these interrelated parameters helps engineers achieve appropriate dynamic control.

Understanding Threshold

Threshold represents the level above which compression activates. When signal exceeds threshold, the compressor begins reducing gain. When signal falls below threshold, the compressor doesn’t affect the signal.

Lower threshold settings mean more of the signal gets compressed. Even moderate peaks trigger the compressor. The overall dynamic range reduces significantly.

Higher threshold settings mean only the loudest peaks trigger compression. Most of the signal passes through unaffected. Only extreme peaks receive reduction.

The threshold position determines the character of compression—constant reduction versus peak catching. Neither approach is inherently better; each serves different purposes.

Understanding Ratio

Ratio expresses the relationship between input level above threshold and output level above threshold. A 4:1 ratio means 4 dB of input signal above threshold results in only 1 dB of output above threshold.

Lower ratios like 2:1 or 3:1 provide gentle compression where gain reduction happens gradually. The signal still varies dynamically, just within a narrower range.

Higher ratios like 8:1 or 10:1 provide aggressive compression where peaks are significantly attenuated. The output level remains much more constant.

Extreme ratios of 20:1 or higher approach limiting where the output essentially cannot exceed the threshold. This brick-wall behavior catches all peaks.

Ratio and Threshold Interaction

Low ratio with low threshold produces constant, gentle compression. The compressor engages frequently but reduces gain moderately. This creates smooth, even dynamics.

Low ratio with high threshold produces occasional, gentle compression. Only peaks trigger reduction, and that reduction is moderate. This subtle approach catches peaks while preserving dynamics.

High ratio with low threshold produces constant, aggressive compression. The compressor engages frequently and reduces gain significantly. This heavily compressed sound squashes dynamics.

High ratio with high threshold produces occasional, aggressive compression. Peaks get caught and significantly reduced while quieter material passes through. This peak limiting approach preserves dynamics until limits are reached.

Practical Setting Approaches

Starting with moderate threshold that produces a few dB of reduction on peaks, then adjusting ratio to achieve desired control, provides a methodical approach. This method focuses on the result rather than arbitrary settings.

Watching the gain reduction meter reveals how the compressor responds. Constant reduction indicates low threshold. Occasional reduction indicates high threshold. The amount of reduction reflects the ratio’s effect.

Comparing compressed and uncompressed versions (using bypass) reveals the compression’s impact. The comparison should confirm that compression serves the music.

Genre and Application Considerations

Vocals typically use moderate ratios around 3:1 to 6:1 with threshold set for consistent gain reduction. This provides the even dynamics vocal mixing requires.

Drums often use higher ratios for punch, with threshold set to catch transients. The aggressive settings suit the genre expectations for powerful drums.

Bus compression typically uses lower ratios with threshold catching peaks. The gentle, musical compression provides glue without squashing.

Mastering limiters use extreme ratios with high thresholds. The brick-wall limiting catches any peaks that would cause clipping while preserving most dynamics.

Proper ratio and threshold settings help productions succeed on platforms like LG Media at lg.media, where controlled dynamics enhance advertising at $2.50 CPM.