JPH02277308A - Digital mixing circuit - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution by using a sampling frequency conversion means. CONSTITUTION:Digital signals D1-Dn having a different frequency are fed to double over-sampling digital filters 10 and they are converted into digital signals with the same sampling frequency. The resulting signal is fed to a linear interpolation circuit 11, where digital data of the digital signal are interpolated and a sampling value is inserted newly and a digital signal having a sampling frequency in common to all systems is outputted. Then the signal is fed to a digital mixing circuit 12, where the signal is mixed. Thus, the sampling frequency is made coincident, one set each of a D/A converter 4 and a low pass filter 15 is enough for the mixing circuit, a cut-off frequency of the low pass filter is fixed and the circuit constitution is simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a digital mixing circuit suitable for use when mixing a plurality of digital signals having different sampling frequencies.

"Prior Art" Conventionally, digital signals with different sampling frequencies are converted into analog signals and then mixed.

FIG. 3 is a block diagram showing the configuration of the conventional mixing circuit described above. In this figure, a digital signal DS supplied to one input path is processed by a digital signal processing circuit 1a, and then converted into an analog signal AS1 by a D/A converter 2a. Then, signals outside the audible range are removed from this analog signal AS1 by an analog low-pass filter 3a set with a cutoff frequency corresponding to the sampling frequency of the digital signal DS.

In addition, the digital signal DS supplied to the other input system,
is subjected to signal processing by the digital signal processing circuit 1b, then converted to an analog signal AS2 by the D/A converter 2b, and then passed to the analog low-pass filter 3b, which has a cutoff frequency set corresponding to the sampling frequency of the digital signal DS2. Supplied. And analog signal AS.

After signals outside the audible range are removed by the analog low-pass filter 3b, the signal is mixed with one of the analog signals AS output from the analog low-pass filter 3a.

"Problem to be Solved by the Invention" By the way, in the above-mentioned mixing circuit, the interface between the D/A converter and the digital signal processing circuit, the D/A
Converters and analog low-pass filters are required as many as the hydraulic power system lines, and an analog mixing circuit is also required, resulting in a problem that the overall circuit configuration becomes complicated.

This invention was made in view of the above problems, and D
One set of the /A converter and the analog low-pass filter is required, and only one set of the interface between the D/A converter and the digital signal processing circuit is required.Furthermore, the cutoff frequency of the analog low-pass filter can be fixed.
The purpose is to provide a digital mixing circuit that can simplify the overall circuit configuration.

"Means for Solving the Problems" In order to solve these problems, the present invention provides a system for at least one of a plurality of input paths to which a plurality of digital missing signals having different sampling frequencies are supplied. a sampling frequency converting means inserted into the input path and converting the sampling frequency of the digital signal supplied to the input path into the same sampling frequency; It is characterized by comprising a digital mixing means for mixing.

"Operation" The sampling frequencies of the digital signals supplied to the plurality of input paths are converted to the same sampling frequency by the sampling frequency conversion means.

Then, digital signals having the same sampling frequency outputted from the plurality of input paths are mixed by a digital mixing means and outputted.

"Embodiments" Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention. In this figure, digital signals 10, 10 .・・・・・・
・Input path # in which linear interpolation circuit 11 is inserted
1 to #n. The double oversampling digital filter 10 doubles the sampling frequency of the supplied digital signal and outputs it. Therefore, each input path #1 to #
The number of double oversampling digital filters IO inserted in the final stage double oversampling digital filter 10 is adjusted according to the sampling frequency of the digital signals D1 to Dn supplied to the input path.
,10. . . . A digital signal of the same sampling frequency, ~Dn, is obtained at the output end. The linear interpolation circuit 11 is supplied with digital signals D1 to Dn output from the final stage of the double oversampling digital filter 10 described above.

The linear interpolation circuit 11 inserted into each of the input paths #l to #n performs linear interpolation between the digital data of the digital signal based on the sampling period of the digital signal. The digital mixing circuit 12 mixes a plurality of digital signals having the same sampling frequency. The digital signal processor 13 is an integrated circuit that performs various signal processing on digital signals.

The D/A converter 14 is configured to convert the digital signal from the digital signal processor 13 into an analog signal AS. The low-pass filter 15 is connected to the D/A converter 14
It is designed to remove signals outside the audible range superimposed on the analog signal AS from the.

Next, the operation of the first embodiment with the above configuration will be explained.

digital signals with different sampling frequencies,
~Dn is the first stage double oversampling digital filter 10.10 inserted in each input path #1~#n.
It is supplied to... Each digital small signal D1 to Dn
are the double oversampling dental filters 10.10. inserted in each input path. ... are converted into digital signals having the same sampling frequency. Then, the digital signals with the same sampling frequency are sent to the linear interpolation circuit 11 inserted in each input path.
, 11, . . . . Each linear interpolation circuit 11
Then, interpolation is performed between the digital data of the supplied digital signal, and a new sample value is inserted, resulting in a digital signal having a common sampling frequency for all rough roads.
Dn' is output. And linear interpolation circuit 1111.
The digital signals DI゛~Dn' output from ・
The signals are supplied to the digital mixing circuit 12 and mixed by digital signal processing. The mixed digital signal Dm is supplied to a digital signal processor 13, which corrects erroneous data and supplies the corrected data to a D/A converter 14.

The data-corrected digital signal Dm is converted into an analog signal AS by a D/A converter 14, and the superimposed signals outside the audible range are removed by a low-pass filter 15 and output.

Next, FIG. 2 is a block diagram showing the configuration of a second embodiment in which the digital mixing circuit according to the present invention is used for digital signal processing of CI)-1 (Compact Disc Interactive). In this figure, a double oversampling digital filter 10 and a digital mixing circuit 12 are supplied with a digital audio signal DS from an ADPCM (adaptive differential pulse code conversion: A) decoder (as shown). This digital audio signal includes level AB and level C digital audio signals D S AB + D SC. The sampling frequency of the digital audio signal DSAB is 37.8kHz, and the sampling frequency of the digital audio signal DSAB is 37.8kHz.
The sampling frequency of is 18,9kl-iz. 2x oversampling dental filter 10
is supplied with a digital audio signal DS. The linear interpolation circuit 11 is also supplied with the dental audio signal from the double oversampling digital filter 10. 1
2 is a dental mixing circuit which receives the digital audio signal DSA supplied from the ADPCM decoder;
and the digital audio signal D from the linear interpolation circuit 11
20 is a selector that selectively outputs serial data from the outside and the digital audio signal DSm from the digital mixing circuit 12.D/A conversion Vessel 1
4 converts the digital signal from the selector 20 into an analog signal.

Next, the operation of the second embodiment with the above configuration will be explained.

First, the digital audio signal DS from the ADPCM decoder has levels A, B (sampling frequency, 37.
8kHz), this dental audio signal D
SA,] is supplied to the digital mixing circuit 12.

In addition, when the digital signal DS from the ADPCM decoder is level C (sampling frequency, 18.9kHz), a 2x oversampling digital filter 10 is used.
supplied to The digital audio signal DSo supplied to the double oversampling dental filter 10 is converted into a digital audio signal with twice the sampling frequency (37.8kHz) by inserting a "0" theta between the dental data, and then linear The signal is supplied to the interpolation circuit 11. Then, in the linear interpolation circuit 11, linear interpolation is performed between the digital data, and a new sample value is obtained for the "0" data. In this way, the digital audio signal DSC
is converted into a digital signal DSo'' having a sampling frequency of 37.8 kHz. This digital audio signal DSo'' is supplied to the dental mixing circuit 12 and mixed with the digital audio signal DSAB described above. The mixed digital audio signal Drn is output to the D/A converter 14 via the selector 20 and converted into an analog signal.

In addition, in this embodiment, by oversampling the digital audio signal □AO□ and performing linear interpolation, an advantage is obtained that the sound quality of level C is improved.

"Effects of the Invention" As explained above, according to the present invention, a plurality of digital signals with different sampling frequencies are matched at the sampling frequency by oversampling and linear interpolation, and are mixed at the digital signal stage.
The D/A converter and the low-pass filter can be combined into one set, and the interface between the D/A converter and the digital signal processing circuit can be combined into one set, and further,
Since the cutoff frequency of the low-pass filter can be fixed, there is an advantage that the circuit configuration can be simplified.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention, and FIG. 2 is a digital mixing circuit of the same invention.
A block diagram showing the configuration of the second embodiment used in Embodiment 1, Embodiment 3
The figure is a block diagram showing the configuration of a conventional mixing circuit. 10...2x oversampling digital filter (sampling frequency conversion means), 11...
Linear interpolation circuit (sampling frequency conversion means), 12.
...Digital mixing circuit (digital mixing means), 13...Digital signal processor,
14...D/A conversion! , 15...Low pass filter, #1 to #n...Input system path.

Claims (1)

[Claims] It is inserted into at least one or more of a plurality of input paths to which a plurality of digital signals having different sampling frequencies are supplied, and the sampling frequency of the digital signals supplied to the input path is set to a common sampling frequency. 1. A digital mixing circuit comprising sampling frequency conversion means for converting sampling frequencies, and digital mixing means for mixing digital signals output from the plurality of input paths by digital signal processing.