A digitised audio signal, such as an amateur's singing, and a digital guide audio signal are supplied to a time alignment process that produces a time-aligned new signal, time-aligned to the guide signal. Pitch along the time-aligned new signal and along the guide signal is measured in processes and which supply these measurement to a pitch adjustment calculator which calculates a pitch correction factor C's(Fps) from these measurements and the nearest octave ratio of the signals. A pitch changing process modulates the pitch of the time-aligned new signal to produce a time-aligned and pitch adjusted new signal.