Arguments: reference, input
Bal comes from the csound opcode "balance". Bal will take an input signal, and match the amplitude of the signal with a reference signal.
Typically bal is used as a tool with filters like moogladder whose topology often reduces the gain of the input signal. The example below shows this typical usecase, splitting the input value into a filtered input signal and a dry reference signal. These values go into bal to add makeup gain.
150 0.3 saw dup 0.1 1 sine 200 1000 biscale 0.3 moogladder bal