Abstract: A signal processing system for adjusting an audio signal, the signal processing system configured to: receive an audio signal for adjustment at a signal input; at a function generator, receive a selection of a musical key and scale, the musical key and scale including musical notes, and generate an audio signal processing function, configured to adjust the amplitude of frequencies of an audio signal, the audio signal processing function being dependent on the selected musical key and scale; apply the generated audio signal processing function to the received audio signal to generate an adjusted audio signal; and, output the adjusted audio signal at a signal output.