Audio personalisation method and system

1. An audio personalisation method for a user, to reproduce an area-based or volumetric sound source, comprising the steps of:

for a head related transfer function ‘HRTF’ associated with the user,

smoothing HRTF coefficients relating to peaks and notches in the HRTF's spectral response, responsive to the size of the area or volume of the sound source;

filtering the sound source using the smoothed HRTF for the notional position of the sound source; and

outputting the filtered sound source signal for playback to the user.

2. An audio personalisation method according to claim 1 , in which the step of outputting the filtered sound source comprises outputting a plurality of instances of the filtered sound source with global delays distributed according to the range of distances from the user occupied by the sound source.

3. An audio personalisation method according to claim 2 , in which the sound source is filtered using a smoothed HRTF for several notional positions, and a different global delay is used for at least one of the notional positions.

4. An audio personalisation method according to claim 1 , in which the step of smoothing coefficients of the HRTF comprises smoothing the coefficients proportionally to the size of the area or volume of the sound source.

5. An audio personalisation method according to claim 1 , in which the HRTF is smoothed using one or more of:

i. a moving average filter;

ii. a spatial smoothing filter; and

iii an averaging of HRTF coefficients for two or more adjacent HRTF positions.

6. An audio personalisation method according to claim 1 , comprising the steps of:

applying a random phase delay for each of a plurality of copies of the smoothed HRTF; and

summing the results.

7. An audio personalisation method according to claim 1 , in which the step of outputting the filtered sound uses ambisonics.

8. An audio personalisation method according to claim 7 , in which the sound is played on one or more ambisonic channels corresponding to a spatial distribution of the area-based or volumetric sound source.

9. An audio personalisation method according to claim 7 , in which the sound is additionally played on an omnidirectional channel.

10. An audio personalisation method according to claim 1 , in which the step of outputting the filtered sound source for playback to the user is part of a test to identify a previously prepared HRTF for the user from among a library of HRTFs.

11. A non-transitory, computer readable storage medium containing a computer program comprising computer executable instructions adapted to cause a computer system to perform an audio personalisation method for a user, to reproduce an area-based or volumetric sound source, comprising the steps of:

for a head related transfer function ‘HRTF’ associated with the user,

smoothing HRTF coefficients relating to peaks and notches in the HRTF's spectral response, responsive to the size of the area or volume of the sound source;

filtering the sound source using the smoothed HRTF for the notional position of the sound source; and

outputting the filtered sound source signal for playback to the user.

12. An audio personalisation system to reproduce an area-based or volumetric sound source for a user, comprising:

storage configured to hold a head related transfer function ‘HRTF’ associated with the user,

a smoothing processor configured to smooth HRTF coefficients relating to peaks and notches in the HRTF's spectral response, responsive to the size of the area or volume of the sound source;

a filtering processor configured to filter the sound source using the smoothed HRTF for the notional position of the sound source; and

a playback processor configured to output audio signals corresponding to the filtered sound source for the user.

13. An audio personalisation system according to claim 12 in which: the audio personalisation system is configured to play a plurality of instances of the filtered sound source with global delays distributed according to the range of distances from the user occupied by the sound source.

14. An audio personalisation system according to claim 12 , in which: the playback processor outputs audio signals using ambisonics.