Signal processing device, signal processing method, and program therefor
A signal processing device includes a bass signal extractor, a harmonic wave generator, a level detector, and an adjustment controller. The bass signal extractor first extracts a bass signal from an input audio signal. Natural-sounding bass enhancement is achieved as a result of the adjustment controller boosting the bass signal level until the level detector detects the bass signal level at a set level. For input bass signal levels higher than the set level, bass is enhanced virtually using a harmonic signal generated from the bass signal by the harmonic wave generator. As a result, the disadvantages of the boost method and the virtual signal enhancement method are mutually compensated for, and synergistic advantages for bass enhancement are obtained.
1. A signal processing device, comprising:
a bass signal extractor that extracts a low-frequency band signal from an input audio signal;
a harmonic wave generator that generates a harmonic signal from the low-frequency band signal that was extracted by the bass signal extractor;
a level detector that detects a level of the low-frequency band signal extracted by the bass signal extractor;
an adjustment controller that controls an adjustment of both the level of the low-frequency band signal extracted by the bass signal extractor and the level of the harmonic signal generated by the harmonic wave generator, the adjustment being conducted according to the level of the low-frequency band signal detected by the level detector; and
an adder that adds, to the input audio signal, the low-frequency band signal and the harmonic signal that were level-adjusted by the adjustment controller; and
a first filter that applies set signal characteristics to combined signal components that result from the adder adding together the low-frequency band signal, the harmonic signal, and the input audio signal.
2. The signal processing device according to claim 1 , wherein the adjustment controller controls the adjustment of the level of the low-frequency band signal such that an output level of the low-frequency band signal is suppressed to a fixed level, the adjustment being conducted when the level of the low-frequency band signal detected by the level detector becomes greater than a predetermined threshold value.
3. The signal processing device according to claim 1 , wherein the adjustment controller controls the adjustment of the level of the harmonic signal such that
the harmonic signal is not output when the level of the low-frequency band signal detected by the level detector is equal to or less than a predetermined threshold value, and
an output level of the harmonic signal becomes proportional to the detected level of the low-frequency band signal when the level of the low-frequency band signal becomes greater than the predetermined threshold value.
4. The signal processing device according to claim 1 , wherein the adjustment controller
controls the adjustment of the level of the low-frequency band signal such that an output level of the low-frequency band signal is suppressed to a fixed level, the adjustment being conducted when the level of the low-frequency band signal detected by the level detector becomes greater than a first threshold value, and
controls the adjustment of the level of the harmonic signal such that
the harmonic signal is not output when the level of the low-frequency band signal detected by the level detector is equal to or less than a second threshold value, and
an output level of the harmonic signal becomes proportional to the detected level of the low-frequency band signal when the level of the low-frequency band signal becomes greater than the second threshold value.
5. The signal processing device according to claim 1 , wherein the first filter applies signal characteristics that are an inverse of characteristics of a speaker that conducts sound reproduction on the basis of an output signal of the signal processing device.
6. The signal processing device according to claim 5 , wherein the inverse characteristics are calculated on the basis of speaker characteristics measured by causing the speaker to output a reference signal whose low-frequency band has been boosted in advance, the low-frequency band corresponding to the range of frequencies that are extracted by the bass signal extractor.
7. The signal processing device according to claim 1 , further comprising:
a second filter that applies second signal characteristics to the harmonic signal before the harmonic signal is level-adjusted by the adjustment controller.
8. The signal processing device according to claim 7 , wherein the second filter applies the second signal characteristics to the harmonic signal that are an inverse of characteristics of the speaker that conducts sound reproduction on the basis of an output signal of the signal processing device.
9. The signal processing device according to claim 7 , wherein the first filter applies the set signal characteristics that are the inverse of the characteristics of the speaker that conducts sound reproduction on the basis of the output signal from the signal processing device;
wherein the signal processing device further comprises an EQ (equalization) processor that conducts EQ processing to apply required signal characteristics as target characteristics to the combined signal components that result from the adder adding together the low-frequency band signal, the harmonic signal, and the input audio signal; and
wherein the second filter applies signal characteristics to the harmonic signal that are an inverse of the target characteristics of the EQ processor.