Audio signal processing device and audio signal processing method

1. An audio signal processing device generating and outputting 2-channel audio signals acoustically reproduced by two electro-acoustic transducer means arranged at positions close to both ears of a listener from audio signals of plural channels of two or more channels, comprising:

head related transfer function convolution processing units to convolute head related transfer functions with the audio signals of respective channels of the plural channels, which allow the listener to listen to sound such that sound images are localized at assumed virtual sound image localization positions concerning respective channels of the plural channels of the two or more channels when sound is acoustically reproduced by the two electro-acoustic transducer means; and

2-channel signal generation means for generating 2-channel audio signals to be supplied to the two electro-acoustic transducer means from audio signals of plural channels from the head related transfer function convolution processing units,

wherein, in the head related transfer function convolution processing units, at least a head related transfer function concerning direct waves from the assumed virtual image localization positions concerning a left channel and a right channel in the plural channels to both ears of the listener is not convoluted,

wherein a means for not convoluting the head related transfer function concerning direct waves from the assumed virtual sound image localization positions concerning the right and left channels to both ears of the listener is provided at a subsequent stage of the 2-channel signal generation means by convoluting an inverse function of the head related transfer function concerning direct waves from the assumed virtual sound image localization positions concerning the right and left channels to both ears of the listener.

2. The audio signal processing device according to claim 1 , wherein each of the head related transfer function convolution processing units of respective plural channels other than the left and right channels in the plural channels comprises:

a first storage unit to store a direct-wave direction head related transfer function concerning the direct wave direction from a sound source to sound collecting means and a reflected-wave direction head related transfer function concerning selected one or plural reflected-wave directions from the sound source to the sound correcting means which are measured by setting the sound source at the virtual sound localization position and by setting the sound collecting means at positions of the electro-acoustic transducer means, and

a first convolution means for convoluting the direct-wave direction head related transfer function and reflected-wave direction head related transfer function concerning the selected one or plural reflected-wave directions with the audio signal, and

wherein each of the head related transfer function convolution processing units of the left and right channels in the plural channels includes:

a second storage unit to store the reflected-wave direction head related transfer function concerning the selected one or plural reflected-wave directions from the sound source to the sound correcting means which is measured by setting the sound source at the virtual sound localization position and by setting the sound collecting means at positions of the electro-acoustic transducer means, and

a second convolution means for convoluting the reflected-wave direction head related transfer function concerning the selected one or plural reflected-wave directions with the audio signal.

3. The audio signal processing device according to claim 2 ,

wherein the direct-wave direction head related transfer functions and the reflected-wave direction head related transfer functions to be stored in the first storage unit of each of the head related transfer function convolution units are normalized by a head related transfer function concerning direct waves from the assumed virtual sound image localization positions concerning the right and left channels to both ears of the listener.

4. The audio signal processing device according to claim 1 ,

wherein each of the head related transfer function convolution processing units of respective plural channels includes

a storage unit to store a direct-wave direction head related transfer function concerning the direct wave direction from the sound source to the sound collecting means and reflected-wave direction head related transfer function concerning selected one or plural reflected-wave directions from the sound source to the sound correcting means which are measured by setting the sound source at the virtual sound localization position and by setting the sound collecting means at positions of the electro-acoustic transducer means, and

a convolution means for convoluting the direct-wave direction head related transfer function and reflected-wave direction head related transfer function concerning the selected one or plural reflected-wave directions from the storage unit with the audio signals.

5. The audio signal processing device according to claim 2 , 3 or 4 ,

wherein the convolution means executes convolution of the corresponding direct-wave direction head related transfer function and the reflected-wave direction head related transfer function with respect to a temporal signal of the audio signal from a first start point at which convolution processing of the direct-wave direction head related transfer function is started and second start points at which each convolution processing of one or plural reflected-wave direction head related transfer functions is started, the first start point and the second start points being determined according to channel lengths of sound waves from the virtual sound source positions of the direct wave and the reflected waves to the electro-acoustic transducer means.

6. The audio signal processing device according to claim 2 , 3 or 4 ,

wherein the convolution means executes convolution after the reflected-wave direction head related transfer function is gain-adjusted according to an attenuation coefficient of a sound wave at an assumed reflection portion.

7. The audio signal processing device according to claim 2 , 3 or 4 ,

wherein the direct-wave direction head related transfer function and the reflected-wave direction head related transfer function are normalized head related transfer functions obtained by normalizing head related transfer functions measured by picking up sound waves generated at assumed sound source positions by an acoustic-electric transducer means in a state in which the acoustic-electric transducer means is set at positions close to ears of the listener where the electro-acoustic transducer means is assumed to be set and in which a dummy head or a human being is present at the listener's position by using a default-state transfer characteristics measured by picking up sound waves generated at the assumed sound source positions by the acoustic-electric transducer means in the default state where neither the dummy head nor the human being is present at the listener's position.

8. An audio signal processing method in an audio signal processing device generating and outputting 2-channel audio signals acoustically reproduced by two electro-acoustic transducer means arranged at positions close to both ears of a listener from audio signals of plural channels of two or more channels, comprising the steps of:

convoluting head related transfer functions with the audio signals of respective channels of the plural channels by the head related transfer function convolution processing units, which allow the listener to listen to sound such that sound images are localized at assumed virtual sound image localization positions concerning respective channels of the plural channels of the two or more channels when sound is acoustically reproduced by the two electro-acoustic transducer means; and

generating 2-channel audio signals to be supplied to the two electro-acoustic transducer means from audio signals of plural channels as processing results in the head related transfer function convolution processing step by 2-channel signal generation means,

wherein, in the head related transfer function convolution processing step, at least a head related transfer function concerning direct waves from the assumed virtual image localization positions concerning a left channel and a right channel in the plural channels to both ears of the listener is not convoluted,

wherein a step of not convoluting the head related transfer function concerning direct waves from the assumed virtual sound image localization positions concerning the right and left channels to both ears of the listener is performed subsequent to the step of generating the 2-channel signal generation by convoluting an inverse function of the head related transfer function concerning direct waves from the assumed virtual sound image localization positions concerning the right and left channels to both ears of the listener.

9. An audio signal processing device generating and outputting 2-channel audio signals acoustically reproduced by two electro-acoustic transducer units arranged at positions close to both ears of a listener from audio signals of plural channels of two or more channels, the audio signal processing device comprising:

head related transfer function convolution processing units convoluting head related transfer functions with the audio signals of respective channels of the plural channels, which allow the listener to listen to sound such that sound images are localized at assumed virtual sound image localization positions concerning respective channels of the plural channels of the two or more channels when sound is acoustically reproduced by the two electro-acoustic transducer units; and

a 2-channel signal generation unit configured to generate 2-channel audio signals to be supplied to the two electro-acoustic transducer units from audio signals of plural channels from the head related transfer function convolution processing units,

wherein, in the head related transfer function convolution processing units, at least a head related transfer function concerning direct waves from the assumed virtual image localization positions concerning a left channel and a right channel in the plural channels to both ears of the listener is not convoluted,

wherein a unit for not convoluting the head related transfer function concerning direct waves from the assumed virtual sound image localization positions concerning the right and left channels to both ears of the listener is provided at a subsequent stage of the 2-channel signal generation unit by convoluting an inverse function of the head related transfer function concerning direct waves from the assumed virtual sound image localization positions concerning the right and left channels to both ears of the listener.