A method and system for real-time implementation of time-varying head-related transfer functions

A system for real-time implementation of time-varying head-related transfer functions (HRTFs) corresponding to one or more real or virtual sound sources that may be moving relative to a user's head, which system comprises a set of fixed filters (18, 19, 20, 25′) a corresponding filter input addition unit (49, 50, 51, 52) for each of the fixed filters (18, 19, 20, 25′), which filter input addition unit comprises one or more input terminals (a, b, c) such that the set of fixed filters can be used to implement one or more HRTFs corresponding to said one or more real or virtual sound sources, a corresponding controllable gain unit (15, 16, 17, 25) for each of the fixed filters (18, 19, 20, 25′), a controllable delay unit (8) and a filter output addition unit (24), wherein the system further comprises:

• an input configured to receive an input signal (1) and providing the input signal (1) to the controllable delay unit (8), thereby obtaining a delayed version (1′) of the input signal (1);
• where the system is configured for providing the delayed version (1′) of the input signal (1) via each respective of said controllable gain units (15, 16, 17, 25) to the corresponding fixed filter (18, 19, 20, 25′) via a corresponding filter input addition unit (49, 50, 51, 52), thereby obtaining a corresponding delay and gain-adjusted and filtered signal (21, 22, 23, 26) as the output signal of each respective of said fixed filters (18, 19, 20, 25′);
• where the system is configured for providing said one or more delay and gain-adjusted and filtered signals (21, 22, 23, 26) to said filter output addition unit (24) that adds said delay and gain-adjusted and filtered signals provided to the filter output addition unit (24), such that an output signal (10) is provided by the output addition unit (24) that represents the input signal (1) processed through the real-time implementation of an HRTF, which HRTF can be varied solely by varying the delay provided by the delay unit (8) and the gain provided by the respective gain units (15, 16, 17, 25).

A method for real-time simulation of N moving or stationary sound sources in a space surrounding a listener, which method processes N input signals, each of which represents one of the N sound sources, thereby obtaining one or more output signals (10, 66, 92, 93) for a listening device, such as a left output signal (yL(t)) and a right output signal (yR(t)) for a stereophonic headphone (98, 99) or the like, which method comprises using solely a single set of fixed filters (57, 58, 59, 60) to simulate all of said N moving or stationary sound sources, wherein the method for each of said one or more output signals comprises:

• providing one or more fixed filters (57, 58, 59, 60), a corresponding filter input addition unit (49, 50, 51, 52) for each of the fixed filters (57, 58, 59, 60), which filter input addition unit comprises one or more input terminals (a, b, c) such that the set of fixed filters can be used to implement one or more HRTFs corresponding to said one or more real or virtual sound sources, and a common filter output addition unit (65), where the method further comprising for each of said N sound sources providing a respective controllable delay unit (28, 31) and one or more controllable gain units (33, 34, 35, 36;
• 37, 38, 39, 40), where the method further comprises:
• for each of said N sound sources providing information defining the position in space of the respective sound source;
• providing N input signals (27, 30) representing each respective of said N sound sources to the corresponding controllable delay unit (28, 31), thereby obtaining delayed versions (29, 32) of the respective input signals (27, 30);
• providing the delayed version (29, 32) of the input signals (27, 30) via each respective of said controllable gain units (33, 34, 35, 36;
• 37, 38, 39, 40) corresponding to each respective of said N sound sources to the corresponding fixed filter (57, 58, 59, 60) via the corresponding filter input addition unit (49, 50, 51, 52), thereby obtaining a corresponding delayed and gain-adjusted and filtered signal (61, 62, 53, 64) as the output signal of each respective of said fixed filters (57, 58, 59, 60);
• providing said one or more delay and gain-adjusted and filtered signals (61, 62, 63, 64) to said filter output addition unit (65);
• in the filter output addition unit (65) adding said delay and gain-adjusted and filtered signals (61, 62, 63, 64) provided to the filter output addition unit (65), whereby a resulting output signal (10, 66, 92, 93) is obtained that represents the N input signals (27, 30) processed through the real-time implementation of a HRTF corresponding to each respective position in space of the respective sound source, which HRTFs can be varied solely by varying the delay provided by the delay unit (8) and the gain provided by the respective controllable gain units (33, 34, 35, 36;
• 37, 38, 39, 40), and
• providing the resulting output signal (10, 66, 92, 93) to the listening device.