Method of positioning sound image with distance adjustment

A method of positioning a sound image of a virtual sound source to a listener in a virtual sound field by filtering audio signals of left and right channels through left and right filters which simulate acoustic transfer characteristics of the virtual sound field, the method comprising the steps of:

• provisionally memorizing acoustic transfer characteristics of the virtual sound field allotted to sample points distributed radially around a center point of the listener;
• designating a source point at which the virtual sound source is to be located within the virtual sound field in terms of a geometric distance and a geometric direction relative to the center point;
• computing a leftward acoustic direction from the source point to a left ear of the listener according to the geometric distance, the geometric direction and an offset of the left ear from the center point;
• computing a rightward acoustic direction from the source point to a right ear of the listener according to the geometric distance, the geometric direction and an offset of the right ear from the center point;
• selecting a leftward sample point substantially coincident with the leftward acoustic direction to determine an effective acoustic transfer characteristic based on the acoustic transfer characteristic allotted to the leftward sample point so as to enable the left filter to simulate said effective transfer characteristic;
• selecting a rightward sample point substantially coincident with the rightward acoustic direction to determine another effective acoustic transfer characteristic based on the acoustic transfer characteristic allotted to the rightward sample point so as to enable the right filter to simulate said another effective transfer characteristic;
• and
• filtering an audio signal of the left channel through the left filter and filtering another audio signal of the right channel through the right filter to thereby direct the sound image of the virtual sound source located at the source point to the listener positioned at the center point.

An apparatus for positioning a sound image of a virtual sound source at a designated source point to a listener in a virtual sound field, comprising:

• a database that provisionally memorizes acoustic transfer characteristics of the virtual sound field in correspondence to reference source points distributed radially around a center point of the listener;
• left and right filters that respectively filter audio signals of left and right channels according to the acoustic transfer characteristics loaded from the database;
• a processor that computes a leftward acoustic direction from the designated source point to a left ear of the listener, and that computes a rightward acoustic direction from the designated source point to a right ear of the listener;
• a controller that specifies a leftward reference source point coincident with the leftward acoustic direction to load an effective acoustic transfer characteristic corresponding to the leftward reference source point from the database into the left filter, and that specifies a rightward reference source point coincident with the rightward acoustic direction to load another effective acoustic transfer characteristic corresponding to the rightward reference source point from the database into the right filter;
• and
• a feeder that feeds an audio signal of the left channel to the left filter and feeds another audio signal of the right channel to the right filter to thereby direct the sound image of the virtual sound source located at the source point to the listener positioned at the center point.

An apparatus for positioning a sound image of a virtual sound source to a listener in a virtual sound field, comprising:

• a database that provisionally memorizes a pair of leftward and rightward acoustic transfer characteristics of the virtual sound field in correspondence to each of sample points distributed radially around a center point of the listener at a fixed radius, the leftward acoustic transfer characteristic simulating a path from each sample point to a left ear of the listener and the rightward acoustic transfer characteristic simulating another path from each sample point to a right ear of the listener;
• left and right filters that respectively filter audio signals of left and right channels according to the left and right acoustic transfer characteristics loaded from the database;
• an input that designates a source point at which the virtual sound source is to be located within the virtual sound field in a distance which may be different from the fixed radius relative to the center point;
• a processor that computes a leftward acoustic direction from the source point to the left ear of the listener and that computes a rightward acoustic direction from the source point to the right ear of the listener;
• a controller that specifies a leftward sample point substantially coincident with the leftward acoustic direction to load the leftward transfer characteristic corresponding to the leftward sample point from the database into the left filter, and that specifies a rightward sample point substantially coincident with the rightward acoustic direction to load the rightward acoustic transfer characteristic corresponding to the rightward sample point from the database into the right filter;
• and
• a feeder that feeds an audio signal of the left channel to the left filter and feeds another audio signal of the right channel to the right filter to thereby direct the sound image of the virtual sound source located at the source point to the listener positioned at the center point.

An apparatus for positioning a sound image of a virtual sound source relative to a listener in a virtual sound field, comprising:

• a database that provisionally memorizes acoustic transfer characteristics of the virtual sound field in correspondence to sample points distributed radially around a center point of the listener at a fixed radius;
• left and right filters that respectively filter audio signals of left and right channels according to the acoustic transfer characteristics loaded from the database;
• an input that designates a source point at which the virtual sound source is to be located within the virtual sound field in terms of a geometric distance which may be different from the fixed radius and a geometric direction relative to the center point;
• a processor that computes a leftward acoustic direction from the source point to a left ear of the listener according to the geometric distance, the geometric direction and an offset of the left ear from the center point, and that computes a rightward acoustic direction from the source point to a right ear of the listener according to the geometric distance, the geometric direction and an offset of the right ear from the center point;
• a controller that specifies a leftward sample point coincident with the leftward acoustic direction to load an effective acoustic transfer characteristic corresponding to the leftward sample point from the database into the left filter, and that specifies a rightward sample point coincident with the rightward acoustic direction to load another effective acoustic transfer characteristic corresponding to the rightward sample point from the database into the right filter;
• and
• a feeder that feeds an audio signal of the left channel to the left filter and feeds another audio signal of the right channel to the right filter to thereby direct the sound image of the virtual sound source located at the source point to the listener positioned at the center point.

A machine readable medium for use in an apparatus having a CPU and positioning a sound image of a virtual sound source relative to a listener in a virtual sound field by filtering audio signals of left and right channels through left and right filters which simulate acoustic transfer characteristics of the virtual sound field, the medium containing program instructions executable by the CPU for causing the apparatus to perform the steps of:

• provisionally memorizing acoustic transfer characteristics of the virtual sound field allotted to sample points distributed radially around a center point of the listener;
• designating a source point at which the virtual sound source is to be located within the virtual sound field in terms of a geometric distance and a geometric direction relative to the center point;
• computing a leftward acoustic direction from the source point to a left ear of the listener according to the geometric distance, the geometric direction and an offset of the left ear from the center point;
• computing a rightward acoustic direction from the source point to a right ear of the listener according to the geometric distance, the geometric direction and an offset of the right ear from the center point;
• selecting a leftward sample point substantially coincident with the leftward acoustic direction to determine an effective acoustic transfer characteristic based on the acoustic transfer characteristic allotted to the leftward sample point so as to enable the left filter to simulate said effective transfer characteristic;
• selecting a rightward sample point substantially coincident with the rightward acoustic direction to determine another effective acoustic transfer characteristic based on the acoustic transfer characteristic allotted to the rightward sample point so as to enable the right filter to simulate said another effective transfer characteristic;
• and
• filtering an audio signal of the left channel through the left filter and filtering another audio signal of the right channel through the right filter to thereby direct the sound image of the virtual sound source located at the source point to the listener positioned at the center point.