1. Field of the Invention
This invention relates to an audio signal processing method and audio signal processing apparatus to perform virtual acoustic image localization processing of a sound source, appropriate for application in, for example, game equipment, personal computers and the like.
2. Description of the Related Art
There widely exists game equipment which performs virtual acoustic image localization processing. In this game equipment and similar (refer to FIG. 4) there is a central processing unit (CPU) 1, consisting of a microprocessor which controls the operations of the overall equipment. Sound source position information, movement information, and other information necessary for virtual acoustic image localization processing by an audio processing unit 2 is transmitted from this CPU 1 to the audio processing unit 2.
In this audio processing unit 2, as shown in FIG. 5, the position and movement information received from the CPU (position information and movement information for virtual acoustic image localization) is used to perform virtual acoustic image localization processing for incoming monaural audio signals. Of course, input signals are not limited to monaural audio signals, and a plurality of sound source signals can be accommodated by performing filter processing according to their respective localization positions and finally adding the results.
As is widely known, by performing appropriate filter processing of monaural audio signals based on the transfer functions from the position at which the acoustic image is to be localized to both the listener's ears (HRTF: Head Related Transfer Function) and the transfer functions from a pair of speakers placed in front of the listener to both the listener's ears, the acoustic image can also be localized in places other than the positions of the pair of speakers, for example, behind or to one side of the listener. In the specification for this patent, this is called virtual acoustic image localization processing. The reproducing device may be speakers, or may be headphones or earphones worn by the listener. The details of the signal processing differ somewhat depending on the device, but in any case the output obtained is a pair of audio signals (stereo audio signals). By reproducing these stereo audio signals using an appropriate pair of transducers (speakers or headphones) SL, SR as shown in FIG. 6, an acoustic image can be localized at an arbitrary position.
As incoming monaural audio signals, for example, signals which are accumulated in memory 3 and which are read out from memory 3 as appropriate, signals which are generated within the CPU 1 or by a sound generation circuit, not shown, and synthesized effect sounds and noise are conceivable. These signals are supplied to the audio processing unit 2 in order to perform virtual acoustic image localization processing.
By associating position information and movement information for the sound source with sound source audio signals, a sound source object can be configured. When there are a plurality of sound source objects for virtual acoustic image localization, the audio processing unit 2 receives from the CPU 1 the position and movement information for each, and the plurality of these incoming monaural audio signals is subjected to the corresponding respective virtual acoustic image localization processing; as shown in FIG. 5, the plurality of stereo audio signals thus obtained are added (mixed) for each of the right and left channels, for output as a pair of stereo audio signals, and in this way virtual acoustic image localization processing is performed for a plurality of sound source objects.
This localization processing of a plurality of virtual acoustic images is performed within the audio processing unit 2. Originally, in this localization processing of a plurality of virtual acoustic images, each time there is a change in the position or movement information computed within the CPU 1 as shown in FIG. 7, this position and movement information is transmitted to the audio processing unit 2, and in this audio processing unit 2 this position and movement information is used to perform virtual acoustic image localization processing, while changing the internal filter coefficients and other parameters each time there is a change.
However, as shown in FIG. 7, when the above processing is performed in the audio processing unit 2 each time there is a change in the position or movement information, when there are frequent changes or updates in the position or movement information, in addition to the usual virtual acoustic image localization processing, changes in internal processing coefficients must also be made within the audio processing unit 2, with the undesired consequence that the signal processing volume becomes enormous.