Audio frequency response processing system

#This present invention relates to the field of audio signal processing and, in particular, to the field of simulating impulse response functions so as to provide for spatialization of audio signals.

#The human auditory system has evolved accurately to locate sounds that occur within the environment of the listener. The accuracy is thought to be derived primarily from two calculations carried out by the brain. The first is an analysis of the initial sound arrival and arrival of near reflections (the direct sound or head portion of the sound) which normally help to locate a sound; the second is an analysis of the reverberant tail portion of a sound which helps to provide an “environmental feel” to the sound. Of course, subtle differences between the sounds received at each ear are also highly relevant, especially upon the receipt of the direct sound and early reflections.

#For example, in FIG. 1, there is illustrated a speaker 1 and listener 2 in a room environment. Taking the case of a single ear 3, the listener 2 receives a direct sound 4 from the speaker and a number of reflections 5, 6, and 7. It will be noted that the arrangement of FIG. 1 essentially shows a two dimensional sectional view and reflections off the floors or the ceilings are not shown. Further, the audio signal to only one ear is illustrated.

#Notwithstanding any other forms which may fall in the scope of the present invention, the preferred forms of the invention will now be described by way of the example only with reference to the accompanying drawings in which;

#FIG. 1 illustrates schematically the process of projection of a sound to a listener in a room environment;

#FIG. 2 illustrates a typical impulse response of a room;

#Research by the present inventor into the nature of measured impulse response functions has lead to various unexpected discoveries which can be utilised to advantageous effect in reducing the computational complexity of the convolution process in audio spatialization. From various measurements made by the present inventor of human listeners to audio spatialization systems the following important factors have been uncovered.

#First, the low frequency components in the tail of an impulse response do not contribute to the sense of an enveloping acoustic space. Generally, this sense of “space” is created by the high frequency (greater than around 300 Hz) portion of the reverberant tail of the room impulse response.

#Secondly, the low-frequency part of the tail of the reverberant response is often the cause of undesirable ‘resonance’ effects, particularly if the reverberant room response includes the modal resonances that are present in almost all rooms. This is often perceived by the listener as “bad equalisation”.