Vocals almost always need compression because singers cannot hold an even level

Few vocalists can sing at a sufficiently even level to sit in a mix without compression: a loud phrase jumps forward while a soft phrase disappears. Compression reduces this dynamic range, bringing up quiet passages and taming loud ones so the vocal stays consistently present without constant fader rides. Soft-knee compressors are the least obtrusive; for warmth and excitement an opto-compressor or a hard-knee model at a higher ratio adds character. Two side effects to watch: compression raises background noise (about 1 dB for every 1 dB of gain reduction in quiet passages), and heavy compression exaggerates vocal sibilance.

Examples

A vocal with a wide dynamic range: a soft-knee compressor at a moderate ratio evens the loudest phrases into the mix; switching to a hard-knee, higher-ratio setting instead adds punch and excitement at the cost of more audible noise and sibilance.

Assessment

Explain why a higher-ratio compressor would affect background noise and vocal sibilance more than a low-ratio one at the same threshold; then name two compressor types and describe the character each adds to a vocal.