gain
From TidalCycles userbase
Type: gain :: Pattern Double -> ControlPattern
gain turns a number pattern into a control pattern that specifies volume. Values less than 1 make the sound quieter. Values greater than 1 make the sound louder.
d1 $ gain "1 0.5 1.25" # sound "feel"
d1 $ sound "bd*16" # gain (slow 3 $ sine)