Abstract: An infinite impulse response (IIR) filter is provided for receiving an input signal and outputting a filtered signal. The filter comprises feedback circuitry for feeding back said filtered signal, the feedback circuitry comprising a first delay element for delaying said filtered signal; and a sub-unit, for receiving said delayed filtered signal, for outputting a summed signal which is the difference between said delayed filtered signal and a further-delayed filtered signal, and for outputting a multiplied signal which is an inverted further-delayed filtered signal multiplied by a first filter coefficient. At least said input signal, said delayed filtered signal, said multiplied signal, and said summed signal are employed to generate said filtered signal.

Abstract: An infinite impulse response (IIR) filter is provided for receiving an input signal and outputting a filtered signal. The filter comprises feedback circuitry for feeding back said filtered signal, the feedback circuitry comprising a first delay element for delaying said filtered signal; and a sub-unit, for receiving said delayed filtered signal, for outputting a summed signal which is the difference between said delayed filtered signal and a further-delayed filtered signal, and for outputting a multiplied signal which is an inverted further-delayed filtered signal multiplied by a first filter coefficient. At least said input signal, said delayed filtered signal, said multiplied signal, and said summed signal are employed to generate said filtered signal.

Abstract: A mobile electronic device is programmed so that when the device is running a an application and an event occurs that the device needs to notify the user about, then the device alters the visual and/or sonic behaviour of the application according to, a pre-defined event notification profile. The user can select a desired event notification profile from a menu of available profiles stored in the device. For example, the event notification profile could be graphics and/or audio in the application gently fading to an alternative state using a pre-defined transition effect.

Abstract: A method of improving 3D sound reproduction is described, in which virtual sound sources to be positioned behind a listener 10 are filtered using an HF-cut filter in order to remove distracting high-frequency components caused by incomplete transaural crosstalk cancellation. Sound sources placed in the rearward hemisphere of reference sphere 30 are filtered by an amount dependent on the position of the sound source in order to provide a smooth transition between the filtered and unfiltered hemispheres. HF-cut filtering is at a maximum when the sound source is placed directly behind the listener, and is progressively reduced as the forward hemisphere is approached. The invention offers an advantage in that virtual sound images may be placed more effectively behind the listener, given improved realism of 3D effects.

Abstract: A method of processing a single channel audio signal to provide an audio source signal having left and right channels corresponding to a sound source at a given direction in space, includes performing a binaural synthesis introducing a time delay between the channels corresponding to the inter-aural time difference for a signal coming from said given direction, and controlling the left ear signal magnitude and the right ear signal magnitude to be at respective values. These values are determined by choosing a position for the sound source relative to the position of the head of a listener in use, calculating the distance from the chosen position of the sound source to respective ears of the listener, and determining the corresponding left ear signal magnitude and right ear signal magnitude using the inverse square law dependence of sound intensity with distance to provide cues for perception of the distance of said sound source in use.

Abstract: Original head-related transfer functions (HRTFs) are modified for a non-standard dimensioned head. The HRTF includes a near-ear response function, a far-ear response function, and an inter-aural time delay (ITD). The modified HRTF resembles an HRTF approximating that derived for a listener having different head and/or ear dimensions to the standard dimensions. The ITD value of the HRTF is multiplied by a given scaling factor independent of frequency. The near ear and/or far ear response function of the HRTF is multiplied by a constant scaling factor in the frequency domain independent of time delay, to expand or compress the functions in the frequency domain. The near ear and/or far ear response function of the HRTF are provided with a positive or negative offset value in the frequency domain. The amplitude of the near ear and/or far ear response function of the original HRTF(s) is (are) multiplied by a given gain factor.

Abstract: A method of processing a plural channel audio signal representing a three dimensional sound-field for generation by respective left and right loudspeakers arranged at a given distance from a listener, including: a) choosing a distance between said loudspeakers and said listener; b) determining from this chosen distance an optimal amount of transaural acoustic crosstalk compensation, the optimal amount being a function of the chosen distance; and c) applying said optimal amount of crosstalk compensation to said left and right channels. The optimal transaural crosstalk cancellation is preferably achieved using a near ear response transfer function and a far ear response transfer function which asymptotically approach different values at low frequencies. The method may further include choosing an angle between the left channel loudspeaker and the right channel loudspeaker, and determining from both the chosen angle and the chosen distance an optimal amount of transaural crosstalk compensation.

Abstract: A stereo sound expander reproduces a realistic sound image in three dimensions by coupling modified and unmodified stereo signals. By not modifying a Head Related Transfer Function (HRTF) for one signal and equalizing the HRTF for the other signal, a flattened frequency response is produced with no tonal changes, but with a high degree of spatial accuracy. Resultant output signals may be used to generate binaural signals or can be fed into crosstalk cancellers.

Abstract: A method of synthesizing a three dimensional sound-field using a pair of front and a pair of rear loudspeakers, including: a) determining the desired position of a sound source; b) providing a binaural pair of signals corresponding to the sound source using an HRTF filter; c) providing the left signal of said binaural pair of signals to both the left front and left rear loudspeakers through a front and a rear gain control means respectively; d) providing the right signal of said binaural pair of signals to both the right front and right rear loudspeakers through a front and a rear gain control means respectively; e) controlling the ratio of the front signal gains to the rear signal gains as a function of the azimuth angle of the sound source; and f) performing transaural crosstalk cancellation on the front and rear signal pairs through respective transaural crosstalk cancellation means.

Abstract: A filter apparatus (1) has a digital FIR filter (8) divided into two or more sections (6, 12) with means (18, 20, 22, 24, 26, 40) for varying the filter function of each section (6, 12). The filter (1) has an input switch (2,4) and an output switch (28, 30,32) which includes a fader (28, 30, 32) to enable one or more section (6, 12) to be switched out of circuit without disrupting the passage of signals to be filtered through the other section or sections (6, 12) of the filter (8). The filter function of each section (6, 12) is adjustable when the section (6,12) is switched out of circuit.

Abstract: Stereophonic sound reproduction apparatus comprising an input means (2) for producing binaural signals, cross-talk cancellation means, (10) loudspeaker means, (20, 22) headphone means, (26) and a switch means (12, 18, 24, 30, 32) which in a first position (plug 24 not inserted in socket 18) couples the binaural signals from the input means (2) to the loudspeaker means (20, 22) through the cross-talk cancellation means (10) and in a second position (plug 24 inserted in socket 18) renders the cross-talk cancellation means (10) inoperable and couples the binaural signals from the input means (2) to the headphones (26).

Abstract: An audio signal balance control arranged is described in which, by utilizing binaural head related transfer functions, balance control beyond a first plane (22) in which two loudspeakers lie may be achieved. The transfer functions are derived from conventional artificial-head recording techniques with various attitudes of the artificial head in a further plane (25) normal to the first plane (22).

Abstract: An artificial head (2) and a plurality of discrete monophonic microphones (8, 10, 12) are used to record one or more sound sources. The signals (14, 16, 18) from each of the microphones (8, 10, 12) then undergo binaural synthesis based upon acoustical properties of a real human head or the artificial head (2), and the signals (4, 6) from the head are equalised using air-to-ear transfer functions of the artificial head (2) or a real head. The resultant signals are combined by summing the individual left (48) and right (50) channels together and then these summed signals (52, 54) are transaural crosstalk compensated (56) to provide final left and right channel signals (58, 60) suitable for recording or playback which provide a three-dimensional sound effect to a listener both via headphones and loudspeakers.