JP2002319237A - Digital signal processing device and processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To align output signal level, when a processing system is switched and a signal of different kind is processed, in a digital signal demodulation processing. SOLUTION: A PCM signal or a DSD signal, inputted to a digital signal processing device 1, is processed by the prescribed processing system, and the gain of an interpolation filter 20 is set appropriately, so that gain of respective signals matches with each other. In the digital signal processing device 1, a ΔΣmodulator 60 is set to an appropriate value, so that the gain of the final output signal becomes '1'. Therefore, even when a PCM signal and a DSD signal are inputted to the digital signal processing device 1 and the digital signal processing device 1 switches respective input signals and processes it, it is not necessary to successively switch an output signal level ever time input signals are switched, because the gain of demodulated signals of each signal matches with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a digital signal processing method and a digital signal processing apparatus for demodulating a modulated digital signal into an analog signal.

[0002]

2. Description of the Related Art In recent years, DVD (Digital) has been used as a digital music system having a sound quality equal to or higher than that of a CD (Compact Disc).
Video Disc audio system and SACD (Super Au)
Music using the "dio CD" method is becoming widespread. DVD
The audio system uses 24-bit PCM (Pulse Code M).
odulation) is a digital music system based on SAC
D is a digital music system based on the DSD (Direct Stream Digital 1 bit) system. This PCM is a method of quantizing a music signal in the amplitude direction, and the maximum value of the signal is determined by the number of quantization bits. Also, DSD
The method is a method of representing a signal by 1-bit quantization in the time direction, that is, a method of representing a signal amplitude by the density of “0” and “1” signals. Therefore, in the DSD method, the maximum value of a signal is represented by a density portion of "1" on the time axis, and the minimum value (minus maximum value) of the signal is represented by a density portion of "0" on the time axis. Can be represented by

[0003] However, in the DSD system, since a 1-bit signal is generally generated by a Δ で は modulator, the system in which the maximum value of the signal is all “1” and the minimum value is all “0” becomes unstable. There is. Therefore, in the DSD method, in order to secure stability in modulation and demodulation, when the density of the number of bits of “1” or “0” is a constant value, the maximum value and the minimum value of the signal are respectively set.
The maximum value is indicated when the ratio of “1” is 70% and the ratio of “0” is 30%. At this time, the gain is 0.4 as compared with the case where all the maximum values of the signal are represented by “1”.

Here, a conventional audio DAC (Digi
digital signal processing device (PCM signal and DSD for multi-disc player etc.) with tal / Analog Converter
The device to which the signal is switched and input) can switch between the processing of the PCM signal and the processing of the DSD signal according to the type (modulation method) of the input signal. FIG. 2 is a diagram showing a configuration of a conventional digital signal processing device 100. In FIG. 2, the digital signal processing device 100 includes a DATT
(Digital ATTenuator) 101, interpolation filter 102, DATT 103, low-pass filter 104, switch 105, ΔΣ modulator 106
And a D / A conversion filter 107.

[0005] The DATT 101 includes a multiplier.
P which is one of the input signals of the digital signal processing device 100
CM signal and DATT103 to ATT of DATT103
A coefficient (attenuator coefficient) is input. And
The DATT 101 calculates the product of the PCM signal and the ATT coefficient by a multiplier, and outputs the calculation result to the interpolation filter 102. In addition, DATT101
, The gain of the PCM signal input to the
The gain of T101 is also “1”.

[0006] The interpolation filter 102
An interpolating signal for pseudo-oversampling the digital signal input from the DATT 101 is generated, and the interpolated digital signal is output to the switch 105. Note that the gain of the interpolation filter 102 is
It is set to “1”. The DATT 103 receives a DSD signal, which is one of the input signals of the digital signal processing device 100. Then, the DATT 103 converts the input DSD signal into an 8-bit digital signal by multi-bit, adds one bit of information indicating a positive or negative sign, and outputs the resulting signal to the low-pass filter 104. Here, since the DSD signal represents the signal amplitude by a 1-bit signal, attenuation processing by the attenuator cannot be performed as it is. Therefore, the data is multi-bit-converted by the DATT 103 and output to the low-pass filter 104 as a 9-bit digital signal including information indicating a code. In addition, DA
The gain of the DSD signal input to the TT103 is “0.4”
It is.

[0007] The DATT 103 is a set attenuator coefficient (hereinafter referred to as "ATT coefficient").
Is output to DATT101. The ATT coefficient is D
The ATT 103 takes a value according to the information amount allocated to indicate the ATT coefficient inside the ATT 103.
If 8 bits are allocated to indicate the coefficient,
It can take a value from "-256" to "255".

The low-pass filter 104 is a DATT10
The digital signal that has been input from 3 and passes through a multi-bit digital signal at a certain frequency or lower is transmitted, and the digital signal after transmission is output to the switch 105. The low-pass filter 104 is arbitrarily provided according to the circuit characteristics of the digital signal processing device 100.
It is provided to prevent oscillation of the modulator 106. The gain of the low-pass filter 104 is set to “1”.

When a signal is input from either the interpolation filter 102 or the low-pass filter 104, the switch 105 selects the signal and selects ΔΣ
Output to modulator 106. The ΔΣ modulator 106 performs noise shaping processing on the signal input from the switch 105, and outputs a signal in which quantization noise is shifted to outside the audible band to the D / A conversion filter 107. The gain of the ΔΣ modulator 106 is set to “1”.

A D / A conversion filter 107 converts a digital signal input from the ΔΣ modulator 106 into an analog signal and outputs the analog signal. The D / A conversion filter 107
Are the output signals of the digital signal processing device 100. The gain of the D / A conversion filter 107 is “1”.
Is set to With such a configuration, when either the PCM signal or the DSD signal is input, the digital signal processing device 100 processes the input signal by a processing system corresponding to each signal and demodulates the input signal into an analog signal. .

[0011]

However, a digital signal processing apparatus 10 such as a conventional audio DAC is required.
0 is a configuration in which when the demodulation processing of the PCM signal and the DSD signal is switched, their output signal levels are not matched. For example, the PCM of the digital signal processing device 100
The demodulated signal of the signal has a gain of “1”, while the demodulated signal of the DSD signal has a gain of “0.4”. Therefore, a difference in the output signal level occurs, such as a difference in the output audio level, and there has been a problem that the output signal level needs to be adjusted every time the demodulation processing system is switched.

An object of the present invention is to match output signal levels when processing different types of signals by switching processing systems in digital signal demodulation processing.

[0013]

In order to solve the above-mentioned problems, the invention according to claim 1 provides a demodulation processing means (for example, FIG. 1) for performing a predetermined demodulation process based on a specific modulation method.
DATT10 and interpolation filter 2
0 or a processing system including the DATT 30 and the low-pass filter 40), and performs a subsequent predetermined demodulation process on the output signal processed by the predetermined demodulation processing means according to the modulation method of the input signal. A digital signal processing device including common processing means for applying (for example, the switch 50, the ΔΣ modulator 60, and the D / A conversion filter 70 in FIG. 1), wherein the demodulation processing means of the first modulation method includes a second modulation method. The gain can be set so that the output signal level matches the output signal level of the demodulation processing means of the system.

According to a sixth aspect of the present invention, a demodulation process for performing a predetermined demodulation process based on a specific modulation system can be executed for a plurality of modulation systems, and a predetermined demodulation process can be performed according to a modulation system of an input signal. A digital signal processing method including a common processing step of performing a subsequent predetermined demodulation processing on an output signal processed through the demodulation processing step of the first modulation method, wherein the demodulation processing step of the first modulation method includes the step of: The gain can be set so that the output signal level matches the output signal level in the demodulation processing step of the system.

According to a second aspect of the present invention, there is provided the digital signal processing apparatus according to the first aspect, wherein the demodulation processing means of the first modulation method comprises an output signal level of the demodulation processing means of the second modulation method. An interpolation filter (for example, the interpolation filter 20 in FIG. 1) capable of changing the gain so as to have an output signal level that matches the digital signal for demodulation processing based on the first modulation scheme. By changing the gain of the interpolation filter, the gain of the demodulation processing means of the first modulation method can be adjusted.

According to a seventh aspect of the present invention, there is provided the digital signal processing method according to the sixth aspect, wherein the demodulation process of the first modulation method is an output of the demodulation process of the second modulation method. The gain can be changed so that the output signal level matches the signal level, and the method includes an interpolation step of interpolating a digital signal for demodulation processing based on the first modulation scheme, and changing the gain of the interpolation step. The gain of the demodulation process of the first modulation method can be adjusted.

The third aspect of the present invention is the first or second aspect.
In the digital signal processing device described in the above, the common processing means has a gain such that a demodulated signal level is the same as a signal level before modulation. The invention according to claim 8 is the digital signal processing method according to claim 6 or 7, wherein the common processing step has a gain such that a demodulated signal level is the same as a signal level before modulation.

According to a fourth aspect of the present invention, in the digital signal processing apparatus according to any one of the first to third aspects, the common processing means selects one of the plurality of demodulation processing means. Selection means (for example, switch 50 in FIG. 1)
Performing noise shaping processing on the output signal of the demodulation processing means selected by the selection means.
Modulating means (for example, ΔΣ modulator 60 in FIG. 1);
D / A for converting the output signal of the modulation means into an analog signal
Conversion filter (for example, D / A conversion filter 7 in FIG. 1)
0), and the ΔΣ modulation means or the D / A
The gain of the common processing means can be adjusted by changing any gain of the conversion filter.

Further, the invention according to claim 9 provides the invention according to claims 6 to
8. The digital signal processing method according to any one of 8 above,
The common processing step includes a selection step of selecting any of the plurality of demodulation processing steps, and a ΔΣ modulation step of performing noise shaping processing on an output signal of the demodulation processing step selected by the selection step. A D / A conversion filtering step of converting the output signal of the ΔΣ modulation step into an analog signal, wherein the gain of either the ΔΣ modulation step or the D / A conversion filtering step is changed to obtain the common signal. The gain of the process can be adjusted.

According to a fifth aspect of the present invention, there is provided the digital signal processing device according to any one of the first to fourth aspects, wherein
(Pulse Code Modulation) signal or DSD (Direc)
t Stream Digital 1bit) signal can be demodulated.
The invention according to claim 10 is the digital signal processing method according to any one of claims 6 to 9, wherein the PCM signal or the DSD signal can be demodulated.

According to the present invention, after subjecting an input signal to a predetermined demodulation process based on a specific modulation scheme, the gain of the signal is the same regardless of the demodulation processing system.
Even when input signals of different modulation schemes are switched and input and the demodulation processing system changes, there is no need to sequentially adjust the demodulated signal level (output signal level). According to the third and eighth aspects of the present invention, the demodulated signal level can be made equal to the signal level before modulation, and the demodulated signal level can be made appropriate.

[0022]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a digital signal processing apparatus according to an embodiment of the present invention.
FIG. 1 is a diagram illustrating a configuration of a digital signal processing device 1 according to the present embodiment. In FIG. 1, a digital signal processor 1 includes a DATT 10, an interpolation filter 20, a DATT 30, and a low-pass filter 40.
, A switch 50, a ΔΣ modulator 60, and a D / A conversion filter 70.

In FIG. 1, DATTs 10 and 30, a low-pass filter 40, a switch 50, and a D / A conversion filter 70 have the configuration of a conventional digital signal processor 100.
DATT 101, 103, low-pass filter 104,
The description is omitted because they are the same as the switch 105 and the D / A conversion filter 107, respectively, and the interpolation filter 20 and the ΔΣ modulator 60
Will be described.

The interpolation filter 20 has a D
An interpolation signal for pseudo-oversampling the digital signal input from the ATT 10 is generated, and the interpolated digital signal is output to the switch 50. here,
The gain of the interpolation filter 20 is set to “0.4” in accordance with the gain of the DSD signal, and the gain of the digital signal input to the switch 50 is matched.

The ΔΣ modulator 60 outputs a signal from which quantization noise has been removed by performing noise shaping processing on the signal input from the switch 50 to the D / A conversion filter 70. Here, the interpolation filter 20
Since the gain of the digital signal input from the low-pass filter 40 is “0.4”, the gain of the ΔΣ modulator 60 is set to “2.5”, which is the same as that of the signal before modulation. The gain is adjusted to the same level (that is, the same level as the signal level before modulation).

With the above-described configuration, the digital signal (PCM signal or DSD signal) input to the digital signal processing device 1 is converted into a predetermined processing system (a processing system including the DATT 10 and the interpolation filter 20 or a DATT 30 and a low-pass system). The gain of the interpolation filter 20 is processed by a processing system including the filter 40, and the gain of the interpolation filter 20 is set to an appropriate value (“ 0.4 "). Also, in the digital signal processing device 1, ΔΣ is set so that the final output signal gain becomes “1” with respect to the output signal of each processing system.
The gain of modulator 60 is set to an appropriate value ("2.5").

Therefore, the digital signal processing device 1
Even when the CM signal and the DSD signal are input and the digital signal processing device 1 switches and processes each input signal, since the gain (signal level) of the demodulated signal of each signal matches, each time the input signal is switched. Therefore, there is no need to sequentially switch the output signal level. In the present embodiment, the gain of the ΔΣ modulator 60 is adjusted to “2.5” so that the final output signal gain becomes “1” with respect to the output signal of each processing system. As explained, D / A
By adjusting the gain of the conversion filter 70, the final output signal gain may be set to “1”.

In the present embodiment, each functional part of the digital signal processing device 1 has been described as being realized by hardware, but may be realized by software.

[0029]

According to the present invention, after an input signal is subjected to a predetermined demodulation process based on a specific modulation method, the signal gains are the same regardless of the demodulation processing system. Input signals of different systems are switched and input,
Even when the demodulation processing system changes, there is no need to sequentially adjust the demodulated signal level (output signal level).

According to the third and eighth aspects of the present invention, the demodulated signal level can be made equal to the signal level before modulation, and the demodulated signal level can be made appropriate.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a digital signal processing device 1 according to the present embodiment.

FIG. 2 is a diagram showing a configuration of a conventional digital signal processing device 100.

[Explanation of symbols]

 1,100 Digital signal processing device 10, 30, 101, 103 DATT 20, 102 Interpolation filter 40, 104 Low-pass filter 50, 105 Switch 60, 106 ΔΣ modulator 70, 107 D / A conversion filter

Claims (10)

[Claims] A plurality of demodulation processing means for performing a predetermined demodulation process based on a specific modulation method; A digital signal processing device comprising a common processing means for performing a predetermined demodulation processing, wherein the demodulation processing means of the first modulation method has an output signal level that matches the output signal level of the demodulation processing means of the second modulation method. A digital signal processing device characterized in that the gain can be set so that 2. The demodulation processing means of the first modulation method,
An interpolation filter for interpolating a digital signal for demodulation processing based on the first modulation scheme, the gain of which can be changed so that the output signal level matches the output signal level of the demodulation processing means of the second modulation scheme. 2. The digital signal processing apparatus according to claim 1, wherein the gain of the demodulation processing means of the first modulation scheme can be adjusted by changing the gain of the interpolation filter. 3. The digital signal processing apparatus according to claim 1, wherein said common processing means has a gain such that a demodulated signal level is equal to a signal level before modulation. 4. The common processing unit includes: a selection unit that selects any one of the plurality of demodulation processing units; and a noise shaping process for an output signal of the demodulation processing unit selected by the selection unit. Applying a ΔΣ modulation means, and a D / A conversion filter for converting an output signal of the ΔΣ modulation means into an analog signal, by changing a gain of either the ΔΣ modulation means or the D / A conversion filter. 4. The digital signal processing device according to claim 1, wherein a gain of said common processing means is adjustable. 5. The digital signal processing apparatus according to claim 1, wherein the digital signal processing apparatus can demodulate a PCM signal or a DSD signal. 6. A demodulation processing step for performing a predetermined demodulation processing based on a specific modulation scheme can be executed for a plurality of modulation schemes, and is processed through the predetermined demodulation processing step according to a modulation scheme of an input signal. A digital signal processing method including a common processing step of performing a subsequent predetermined demodulation processing on the output signal obtained in the first modulation scheme, wherein the output signal of the second modulation scheme demodulation processing step is used in the first modulation scheme demodulation processing step. A digital signal processing method, wherein a gain can be set so that an output signal level coincides with the level. 7. The demodulation processing step of the first modulation method,
The gain can be changed so that the output signal level matches the output signal level of the demodulation processing step of the second modulation scheme, and an interpolation step of interpolating a digital signal for demodulation processing based on the first modulation scheme is performed. 7. The digital signal processing method according to claim 6, wherein the gain of the demodulation process of the first modulation method can be adjusted by changing the gain of the interpolation process. 8. The digital signal processing method according to claim 6, wherein said common processing step has a gain such that a demodulated signal level is equal to a signal level before modulation. 9. The common processing step includes: a selection step of selecting one of the plurality of demodulation processing steps; and a noise shaping processing on an output signal of the demodulation processing step selected by the selection step. Applying a ΔΣ modulation step, and a D / A conversion filtering step of converting an output signal of the ΔΣ modulation step into an analog signal, wherein the gain of either the ΔΣ modulation step or the D / A conversion filtering step is changed. 9. The digital signal processing method according to claim 6, wherein a gain of the common processing step can be adjusted. 10. The digital signal processing method according to claim 6, wherein the PCM signal or the DSD signal can be demodulated.