Audio signal processor for simulating the notional sound source

An Audio Signal Processing system in which gain values are calculated for a plurality of output channels so that, from a notional listening position, a notional sound source may be perceived as being positioned anywhere within a notional listening space. First gain contributions arranged to make a predominant contribution when the perceived position is close to the notional listening position are calculated. Second gain contributions arranged to make a predominant contribution when the perceived positions are not close to the notional listening position are calculated. The first gain contributions and the second gain contributions are combined to produce combined gain values for each output channel.