JPH0795672B2 - Digital phase control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial field of application" The present invention is applied to digital audio equipment, for example, as a digital preamplifier that controls the phase for each frequency component of digital data to perform tone control, or The present invention relates to a digital phase control circuit that can be used as a digital phase correction circuit that corrects a phase shift of an analog low-pass filter (demodulation filter) in the subsequent stage.

“Prior Art” Conventionally, a digital preamplifier that performs tone control of digital data is composed of a recursive digital filter (hereinafter, abbreviated as IIR). When performing high-pitched (treble) adjustment, high-frequency components If the input / output characteristics of the IIR are set so as to increase or decrease with the level of, and the bass (bass) adjustment is performed, the input / output characteristics of the IIR are set so that the level of the frequency component in the bass range increases or decreases.

"Problems to be Solved by the Invention" By the way, when tone control of digital data is performed using IIR, there are the following problems.

That is, when the treble adjustment is performed by IIR, the frequency-phase characteristics are as shown in FIG. 4, and here, in order to emphasize the treble, when the level of the frequency component in the treble range is raised, Along with this, a phase shift occurs. For example, as the level increases by +12 dB, the phase becomes approximately +49
It will be advanced once. As a result, the high level component of digital data is overemphasized due to the synergistic effect of the level increase and the phase shift, and when converted to an analog signal, the rising level of the signal becomes extremely large, so-called unpleasant ears, and the sense of hearing is deteriorated. It is played as an unpleasant sound.

The present invention has been made in view of the above-mentioned circumstances, and it is possible to control only the phase of each frequency component of digital data, which makes it possible to perform appropriate tone control and to provide an analog low-pass filter in the subsequent stage. It is an object of the present invention to provide a digital phase control circuit that can be used also as a digital phase correction circuit for correcting the phase shift of the above.

"Means for Solving Problems" The present invention relates to a digital phase control circuit for giving a phase shift to each frequency component of input digital data and outputting the phase component, for each frequency component of input digital data. A cyclic digital filter having an input / output characteristic that gives a shift and a level variation corresponding to this phase shift, a non-recursive digital filter having an input / output characteristic that cancels the level variation due to the cyclic digital filter, and a desired Tone setting means for setting each value of treble adjustment and bass adjustment, and based on setting data supplied from the tone setting means, input / output characteristics of the cyclic digital filter and the non-cyclic digital filter are set. And an input / output characteristic setting means for setting.

[Operation] According to the configuration described above, first, the input / output characteristic setting unit
Based on the setting data supplied from the tone setting means,
Set the input / output characteristics of the recursive digital filter and the non-recursive digital filter. Then, when the digital data is input, the cyclic digital filter is
A phase shift is given to each frequency component of the digital data, and a level fluctuation corresponding to this phase shift is generated, and the non-recursive digital filter cancels the level fluctuation. That is, only the desired phase shift can be given to the input digital data for each frequency component, which makes it possible to realize proper tone control and also to achieve the phase shift of the analog low-pass filter in the subsequent stage. It can also be used as a digital phase correction circuit for correcting

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention. In this figure, 16-bit digital data supplied from a digital audio device such as a CD player is supplied to an input terminal Tin, and this digital data includes IIR digital filter 1 and a non-recursive digital filter (hereinafter, FIR Output from the output terminal Tout to the D / A converter and the like in the subsequent stage through the (abbreviated) 2 sequentially.
The IIR digital filter 1 and the FIR digital filter 2 are both a 1-chip microcomputer that executes a digital signal processing algorithm at high speed, that is, a DS.
It is composed of P (digital signal processor). Here, the IIR digital filter 1 has a characteristic of giving a phase shift to each frequency component of the input digital data and giving a level fluctuation corresponding to this phase shift. Further, the FIR digital filter 2 has a characteristic of giving only a level change for each frequency component of the input digital data, and no phase shift occurs. Further, in the figure, 3 is a tone setting section for setting respective values of desired treble adjustment and bass adjustment,
Reference numeral 4 is a microcomputer that sets the input / output characteristics of the IIR digital filter 1 and the FIR digital filter 2 based on the setting data supplied from the tone setting unit 3. The digital preamplifier 5 is configured as described above.

In the above-mentioned configuration, the microcomputer 4 is based on the setting data supplied from the tone setting unit 3 and the IIR
The input / output characteristics of the digital filter 1 are set so that the level in the desired frequency range will increase or decrease. As a result, the IIR digital filter 1 in the first stage gives a phase shift to the input digital data for each frequency component. In this case, the digital data output from the IIR digital filter 1 also has a level fluctuation corresponding to the phase shift. On the other hand, the microcomputer 4 sets the input / output characteristics for the FIR digital filter 2 in the next stage so as to cancel the level fluctuation caused by the IIR digital filter 1. As a result, the level fluctuation caused by IIR digital filter 1 is F
Removed with IR Digital 2. By the above operation, it is possible to give only the desired phase shift for each frequency component to the input digital data.
It is possible to realize proper tone control without excessively emphasizing a specific frequency range due to the synergistic effect of phase shift and level fluctuation, unlike a digital preamplifier that is configured only by a conventional IIR.

Here, when treble adjustment is performed by the digital preamplifier 5 described above, the response characteristic thereof is as shown in FIG.

In this figure, Din represents digital data corresponding to a 1 KHz rectangular wave input to the digital preamplifier 5, and is shown by combining rectangular waves decomposed from the fundamental wave to the 11th harmonic. Dout is digital data output from the digital preamplifier 5, and each of the harmonic waves from the fundamental wave to the 11th harmonic wave of the rectangular wave is based on each phase characteristic obtained from the +12 dB curve shown in FIG. The shifted results are shown as a composite, and it is assumed that there is no level fluctuation for each harmonic. As shown in this figure, it can be seen that the high frequency region is appropriately emphasized only by the phase shift.

Next, FIG. 2 is a block diagram showing the configuration of the second embodiment of the present invention. In this figure, 6 is a digital phase correction circuit in which the IIR digital 1 and the FIR digital 2 described above are connected in series, and the digital data output from the output terminal Tout is analogized by the D / A converter 7 in the subsequent stage. The signal is converted into a signal and then supplied to the analog amplifier at the next stage through the analog low pass filter 8. In this case, the digital phase correction circuit 6 functions to correct the phase shift generated by the analog low-pass filter 8, whereby the phase distortion that has occurred in the conventional analog signal can be removed.
It is possible to prevent deterioration of sound quality.

[Advantages of the Invention] As described above, according to the present invention, a cyclic shift is provided for each frequency component of input digital data, and an input / output characteristic having a level fluctuation corresponding to the phase shift is generated. Type digital filter, a non-recursive digital filter having input / output characteristics for canceling level fluctuations by the recursive digital filter, tone setting means for setting desired treble adjustment and bass adjustment values, and the tone setting Since the input / output characteristic setting means for setting the input / output characteristics of the recursive digital filter and the non-recursive digital filter based on the setting data supplied from the means, the non-recursive digital filter is used to Cancels the level fluctuations caused by the recursive digital filter of Only the desired phase shift can be given to the input digital data for each frequency component, and as a result, a specific frequency range is excessive as in the digital preamplifier configured only by the conventional recursive digital filter. The effect that suitable tone control can be realized without being emphasized in the above, and can be used as a digital phase correction circuit for correcting the phase shift of the analog low-pass filter in the subsequent stage. Is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of the second embodiment of the present invention, and FIG. 3 is a rectangle in the first embodiment of the present invention. FIG. 4 is a graph showing a response characteristic to digital data corresponding to a wave, and FIG. 4 is a graph showing a frequency-phase characteristic of a recursive digital filter. 1 ... IIR (recursive) digital filter, 2 ... FIR
(Non-recursive) digital filter.

Claims (1)

[Claims] 1. A digital phase control circuit for providing a phase shift for each frequency component of input digital data and outputting the same, in addition to providing a phase shift for each frequency component of the input digital data, A cyclic digital filter having an input / output characteristic that causes corresponding level fluctuation, a non-cyclic digital filter having an input / output characteristic that cancels the level fluctuation by the cyclic digital filter, and desired treble adjustment and bass adjustment values Tone setting means for setting, and input / output characteristic setting means for setting respective input / output characteristics of the recursive digital filter and the non-recursive digital filter based on the setting data supplied from the tone setting means. A digital phase control circuit comprising.