Audio signal processing device
An audio signal processing device receives a plurality of audio signals via a left channel (L) and a right channel (R) so as to produce a composite signal L+R and a difference signal L−R. The composite signal L+R is changed in phase with an all-pass filter, while the difference signal L−R is changed in phase and frequency characteristic with a band-pass filter (e.g. a center frequency of 1 kHz). The band-pass filter has a gently curved frequency characteristic achieving a broad passing band. Additionally, a phase difference of 90 degrees is maintained between the all-pass filter and the band-pass filter over the entire audio frequency range. The composite signal and the difference signal are adjusted in their levels and then mixed together to produce a monaural signal achieving an audio surround effect for widely propagating sound into the surrounding space without degrading sound quality.
1. An audio signal processing device comprising:
an input part receiving a plurality of audio signals via a plurality of channels;
a composite signal generator generating a composite signal adding the plurality of audio signals via different channels;
a difference signal generator generating a difference signal subtracting the plurality of audio signals via different channels;
a phase-shift processor changing a phase of the composite signal;
a frequency processor changing a frequency characteristic of the difference signal and changing a phase of the difference signal depending on a phase variation applied to the composite signal with the phase-shift processor; and
an output part mixing the composite signal and the difference signal already subjected to the phase-shift processor and the frequency processor.
2. The audio signal processing device according to claim 1 , wherein a predetermined phase difference is maintained between the composite signal and the difference signal over an entire audio frequency range.
3. The audio signal processing device according to claim 1 , wherein the frequency processor is a band-pass filter.
4. The audio signal processing device according to claim 3 , wherein a center frequency of the band-pass filter is set to a frequency causing a significant impact on sound localization.
5. The audio signal processing device according to claim 3 , wherein the phase-shift processor is an all-pass filter, and wherein the band-pass filter maintains a predetermined phase difference with the all-pass filter over an entire audio frequency range.
6. The audio signal processing device according to claim 4 , wherein the phase-shift processor is an all-pass filter, and wherein the band-pass filter maintains a predetermined phase difference with the all-pass filter over an entire audio frequency range.
7. The audio signal processing device according to claim 4 , wherein the band-pass filter has a broad passing band ranging from 300 Hz to 5 kHz.
8. The audio signal processing device according to claim 5 , wherein the band-pass filter has a broad passing band ranging from 300 Hz to 5 kHz, and wherein the predetermined phase difference is set to 90 degrees.
9. The audio signal processing device according to claim 6 , wherein the band-pass filter has a broad passing band ranging from 300 Hz to 5 kHz, and wherein the predetermined phase difference is set to 90 degrees.
10. An audio signal processing method comprising:
generating a composite signal adding a plurality of audio signals via different channels;
changing a phase of the composite signal;
adjusting the composite signal at a desired level;
generating a difference signal subtracting the plurality of audio signals via different channels;
changing a phase and a frequency characteristic of the difference signal, thus maintaining a predetermined phase difference between the composite signal and the difference signal;
adjusting the difference signal at a desired level; and
mixing the composite signal and the difference signal, thus producing a monaural signal.
11. The audio signal processing method according to claim 10 , wherein the predetermined phase difference is set to 90 degrees.
12. The audio signal processing method according to claim 10 , wherein the frequency characteristic of the difference signal covers a frequency range from 300 Hz to 5 kHz.
13. An audio signal processing device comprising:
an input part receiving a plurality of audio signals via 5.1 channels;
a composite signal generator generating a composite signal using a left-channel signal and a right-channel signal among 5.1 channels;
a difference signal generator generating a difference signal between the left-channel signal and the right-channel signal;
a phase-shift processor changing a phase of the composite signal;
a frequency processor changing a frequency characteristic of the difference signal and changing a phase of the difference signal depending on a phase variation applied to the composite signal with the phase-shift processor; and
an output part mixing the composite signal and the difference signal already subjected to the phase-shift processor and the frequency processor, thus producing a monaural signal.
14. The audio signal processing device according to claim 13 , wherein the composite signal generator generates a secondary composite signal using a rear left-channel signal and a rear right-channel signal among 5.1 channels, wherein the difference signal generator generates a secondary difference signal between the rear left-channel signal and the rear right-channel signal, wherein the phase processor changes a phase of the secondary composite signal while changing the phase of the composite signal, and wherein the frequency processor changes a frequency characteristic of the secondary difference signal while changing the frequency characteristic of the difference signal.