JPH0564287

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DESCRIPTION JPH0564287
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
audio amplifier, and more particularly to an audio amplifier which receives a digital signal.
[0002]
2. Description of the Related Art FIG. 2 shows an example of the configuration of an audio
amplifier which receives a digital signal, performs predetermined digital processing, and outputs
the digital signal. The analog signal is converted into a digital signal by the A / D converter 1 and
supplied to the selector 4. Also, the digital signal is input to the digital interface unit 2, and based
on the operation of the PLL circuit unit 3, the selector 4 receives the demodulated digital signal
of the operation clock synchronized with the input digital signal using the clock generated from
the reference oscillator. Supplied. The digital signal processing unit (DSP) 6 performs
predetermined signal processing on the digital signal of the sampling frequency fsi from the A /
D converter 1 or the digital interface unit 2 selected by the selector 4. This digital signal
processing is performed based on the timing clock based on the reference clock of the PLL
circuit unit 3 from the timing generation unit 9. The digital signal subjected to predetermined
signal processing by the DSP 6 is converted into an analog signal by the D / A converter 7 and
output.
[0003]
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As described above, conventional audio amplifiers operate based on an operating clock
synchronized to an input digital signal. However, in such a conventional audio amplifier, jitter
occurs in the operation clock due to the duty ratio and jitter of the input digital signal, and this
jitter degrades the sound quality during D / A conversion. . If a quartz oscillator is used as the
reference oscillator, the jitter is reduced, but the PLL lock range is narrowed. Therefore,
conditions are given to the frequency range of the input digital signal, and a signal within a
certain accuracy (about 100 ppm error) There is a problem that you can only input. Furthermore,
when the sampling frequency of the input digital signal changes as, for example, 32 KHz, 44 KHz,
48 KHz, if digital processing such as delay or equalizer is performed in the signal processing in
the audio amplifier, the digital processing characteristic Also, the desired processing result can
not be obtained. Therefore, the parameters of the digital processing must be changed in response
to changes in sampling frequency.
[0004]
Therefore, an object of the present invention is to provide an audio amplifier that enables stable
operation that is not affected by jitter of the input signal or a change in sampling frequency.
[0005]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an audio
amplifier according to the present invention is an audio amplifier for performing predetermined
digital signal processing on an input digital signal and outputting the input digital signal, The
input digital signal is converted into a digital signal of a sampling frequency asynchronous to the
input digital signal to perform the predetermined digital signal processing.
[0006]
According to the present invention, jitter of the input digital signal, etc. can be obtained by
converting the input digital signal into the digital signal of the asynchronous reference clock
separately from the sampling frequency of the input digital signal and then performing
predetermined digital signal processing. The sound quality deterioration at the time of D / A
conversion resulting from it is removed.
[0007]
Next, the present invention will be described with reference to the drawings.
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FIG. 1 is a block diagram showing an embodiment of an audio amplifier according to the present
invention.
In FIG. 1, components denoted by the same reference numerals as in FIG. 2 indicate components
having the same functions.
One of the digital signals supplied from the A / D converter 1 and the digital interface unit 2 is
selected by the selector 4 and input to the sampling frequency converter 5. In the digital
interface unit 2, demodulation processing based on the reference clock locked to the input digital
signal is performed by the PLL circuit unit 3, and the PLL circuit unit 3 is locked to the input
digital data. A reference clock of 128 fsi, 256 fsi or 384 fsi is generated and supplied to the
sampling frequency converter 5.
[0008]
The sampling frequency conversion unit 5 converts the digital signal of the sampling frequency
fsi into the digital signal of the reference clock fso from the clock generator 8 and sends it to the
DSP 6 together with the calculated interpolation data. The DSP 6 executes digital signal
processing as described above based on the reference clock from the clock generator 8 and
sends it to the D / A converter 7. An analog signal converted by the D / A converter 7 is obtained
as an output signal.
[0009]
As described above, in this embodiment, after the output of the sampling frequency converter 5,
the operation is based on a fixed clock independent of the sampling frequency of the input digital
signal. The generation of the fixed (reference) clock is not limited to the built-in oscillator, and an
external oscillator may be used.
[0010]
As described above, the audio amplifier according to the present invention converts the input
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digital signal into the digital signal of the reference clock which is separate from the sampling
frequency of the input digital signal and which is asynchronous with the reference signal and
then performs predetermined digital signal processing. Since this process is performed, not only
the sound quality deterioration at the time of D / A conversion caused by the jitter of the input
digital signal can be removed, but also the operation parameters in the DSP can be fixed, so that
the configuration is simplified. Further, since jitter of the reference clock of the PLL circuit of the
digital interface does not affect the output side, jitter of the reproduction clock by the PLL circuit
may be large, and as a result, the PLL circuit with a wide operating frequency range is used be
able to.
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