gain — Adjusts the amplitude audio signal according to a root-mean-square value.
ihp (optional, default=10) -- half-power point (in Hz) of a special internal low-pass filter. The default value is 10.
iskip (optional, default=0) -- initial disposition of internal data space (see reson). The default value is 0.
asig -- input audio signal
gain provides an amplitude modification of asig so that the output ares has rms power equal to krms. rms and gain used together (and given matching ihp values) will provide the same effect as balance.