Digital amplifier apparatus and method of muting digital amplifier apparatus

1. A digital amplifier apparatus, comprising:

gain-adjusting means for adjusting a gain of a digital audio signal;

dither-superposing means for superposing a predetermined dither on the digital audio signal;

pulse-width-modulated signal generating means for generating a pulse-width-modulated signal corresponding to the digital audio signal;

amplifying means for causing a switching element to perform a switching operation in accordance with the pulse-width-modulated signal;

pulse-width changing means for changing a ratio between a “high” state and a “low” state of the pulse-width modulated signal; and

control means for performing a muting process by causing the gain-adjusting means to set the gain of the digital audio signal to a zero level, the dither-superposing means to stop superposing the dither, and the pulse-width changing means to change, step by step, the ratio between the “high” state and the “low” state of the pulse-width modulated signal toward the “low” state upon receipt of a predetermined muting signal for muting the digital audio signal, thereby maintaining the “low” state and stopping the switching operation performed in accordance with the pulse-width modulated signal.

2. The digital amplifier apparatus according to claim 1 , wherein the amplifying means is an amplifier circuit of a Bridge-Tied Load (BTL) type that includes two of the switching elements for performing a switching operation in accordance with the pulse-width-modulated signal.

3. The digital amplifier apparatus according to claim 1 , wherein the control means performs a muting-release process a predetermined time after performing the muting process.

4. A digital amplifier apparatus, comprising:

gain-adjusting means for adjusting a gain of a digital audio signal;

dither-superposing means for superposing a predetermined dither on the digital audio signal;

pulse-width-modulated signal generating means for generating a pulse-width-modulated signal corresponding to the digital audio signal;

amplifying means for causing a switching element to perform a switching operation in accordance with the pulse-width-modulated signal;

waveform-cycle end detecting means for detecting an end of each waveform cycle of the pulse-width-modulated signal; and

control means for performing a muting process by causing the gain-adjusting means to set the gain of the digital audio signal to a zero level, the dither-superposing means to stop superposing the dither, and the waveform-cycle end detecting means to change a ratio between a “high” state and a “low” state of the pulse-width modulated signal toward the “low” state by using the cycle of the waveform as a trigger upon receipt of a predetermined muting signal for muting the digital audio signal, thereby maintaining the “low” state and stopping the switching operation performed in accordance with the pulse-width modulated signal.

5. A method of muting a digital amplifier that adjusts a gain of a digital audio signal, adds a predetermined dither to the digital audio signal and generates a pulse-width modulated signal corresponding to the digital audio signal having the dither added, the method comprising:

recognizing a muting command upon receiving a predetermined muting signal for muting the digital audio signal;

setting the gain of the digital audio signal to a zero level and then stopping superposing of the dither when the muting command is recognized;

generating the pulse-width modulating signal by performing a switching operation in accordance with the digital audio signal whose gain has been adjusted; and

changing, step by step, a ratio between a “high” state and a “low” state of the pulse-width modulated signal toward the “low” state, thereby maintaining the “low” state and stopping the switching operation performed in accordance with the pulse-width modulated signal.

6. A method of muting a digital amplifier that adjusts a gain of a digital audio signal, adds a predetermined dither to the digital audio signal and generates a pulse-width modulated signal corresponding to the digital audio signal having the dither added, the method comprising:

recognizing a muting command upon receiving a predetermined muting signal for muting the digital audio signal;

setting the gain of the digital audio signal to a zero level and then stopping superposing of the dither when the muting command is recognized;

generating the pulse-width modulating signal by performing a switching operation in accordance with the digital audio signal whose gain has been adjusted;

detecting an end of each waveform cycle of the pulse-width-modulated signal; and

changing a ratio between a “high” state and a “low” state of the pulse-width modulated signal toward the “low” state by using the cycle of the waveform detected in the waveform-cycle end detecting step as a trigger, thereby maintaining the “low” state and stopping the switching operation.

7. A digital amplifier apparatus, comprising:

a gain-adjusting section operable to adjust a gain of a digital audio signal;

a dither-superposing section operable to superpose a predetermined dither on the digital audio signal;

a pulse-width-modulated signal generating section operable to generate a pulse-width-modulated signal corresponding to the digital audio signal;

an amplifying section operable to cause a switching element to perform a switching operation in accordance with the pulse-width-modulated signal;

a pulse-width changing section operable to change a ratio between a “high” state and a “low” state of the pulse-width modulated signal; and

a control section operable to perform a muting process by causing the gain-adjusting section to set the gain of the digital audio signal to a zero level, the dither-superposing section to stop superposing the dither, and the pulse-width changing section to change, step by step, the ratio between the “high” state and the “low” state of the pulse-width modulated signal toward the “low” state upon receipt of a predetermined muting signal for muting the digital audio signal, thereby maintaining the “low” state and stopping the switching operation performed in accordance with the pulse-width modulated signal.

8. A digital amplifier apparatus, comprising:

a gain-adjusting section operable to adjust a gain of a digital audio signal;

a dither-superposing section operable to superpose a predetermined dither on the digital audio signal;

a pulse-width-modulated signal generating section operable to generate a pulse-width-modulated signal corresponding to the digital audio signal;

an amplifying section operable to cause a switching element to perform a switching operation in accordance with the pulse-width-modulated signal;

a waveform-cycle end detecting section operable to detect an end of each waveform cycle of the pulse-width-modulated signal; and

a control section operable to cause the gain-adjusting section to set the gain of the digital audio signal to a zero level, the dither-superposing section to stop superposing the dither, and the waveform-cycle end detecting section to change a ratio between a “high” state and a “low” state of the pulse-width modulated signal toward the “low” state by using the cycle of the waveform as a trigger upon receipt of a predetermined muting signal for muting the digital audio signal, thereby maintaining the “low” state and stopping the switching operation performed in accordance with the pulse-width modulated signal.