setBalance
Sets the stereo balance: -1 is hard left, 0 is centre, 1 is hard right.
An attenuation of the channel being turned away from, never a boost of the other, so a balanced track can never be louder than the same track centred. Only the first two channels move; panning a centre or surround channel is a different feature.
A change is heard after the audio already buffered has drained, which is the ring's depth: at least 200 ms, and longer on Android where the device's own buffer sets it. That is the cost of applying it on the way IN, and it is the right trade here because a balance is set once and left, unlike the volume, which lives on the ring's read side precisely so that it is heard within one device period.
Throws
when value is not finite or is outside -1 to 1.