Patent ID: 7720240

Claim:
A method for processing audio signals for a set of headphones, the method comprising: receiving a plurality of audio signal inputs, each audio signal input comprising information about a spatial position of a sound source relative to a listener; mixing two or more inputs of the plurality of audio signal inputs to produce at least one mixed audio signal; providing the at least one mixed audio signal to first set of positional filters, the first set of positional filters configured to selectively emphasize one or more location-relevant portions of a head-related transfer function (HRTF), the first set of positional filters being implemented as one or more first infinite impulse response (IIR) filters, the first set of positional filters comprising two or more of the following: a first positional filter comprising first component filters, the first component filters comprising a first band stop filter, a first band pass filter, and a first high pass filter, a second positional filter comprising second component filters, the second component filters comprising a second band stop filter, a third band stop filter, and a fourth band stop filter, a third positional filter comprising third component filters, the third component filters comprising a fifth band stop filter, a second band pass filter, and a sixth band stop filter, and a fourth positional filter comprising fourth component filters, the fourth component filters comprising a seventh band stop filter, a third band pass filter, and an eighth band stop filter; passing at least some of the audio signal inputs as unmixed audio signals to a second set of positional filters, the second set of positional filters comprising a second IIR filter, wherein the mixed and unmixed audio signals are arranged such that each audio signal input is provided in mixed and unmixed form to both the first and second sets of positional filters; applying the first set of positional filters to the mixed audio signals and the second set of positional filters to the unmixed audio signals to create a plurality of left channel filtered signals and a plurality of right channel filtered signals respectively; and downmixing the plurality of left channel filtered signals into a left audio output channel and downmixing the plurality of right channel filtered signals into a right audio output channel, such that the spatial positions of the plurality of sound sources are perceptible from the left and right output channels of a set of headphones.