Digital processing requirements for musical sounds are determined both by characteristics of the sounds themselves and by the desired type of control over the synchrony and succession of these sounds. Musical sounds may run the gamut of aural perception, requiring information rates as high as several million bits per second. Signal processing methods must therefore by evaluated from the standpoint of computational speed, as well as the intuitive meaningfulness of control parameters for each method. Those methods peculiar to computer music include additive, subtractive, and non-linear synthesis techniques, as well as procedures for simulating room reverberation. Several versions of real time digital hardware for music processing have been built, each following different design approaches and each with differing real time capabilities.