JPH0287823A - Sampling frequency selection type a/d and d/a converters and signal processing device - Google Patents

Abstract

PURPOSE:To select an optimum sampling frequency in accordance with a signal band included in a prescribed time width by providing a sampling frequency selecting circuit. CONSTITUTION:A frequency component operating circuit 13 for operation of frequency components, a sampling frequency selecting circuit 14, and a decimation circuit 15 are provided. The upper limit value of a required band is operated by the frequency component operating circuit 14 to selectively determine a sampling frequency FRS for resampling. Thinning is performed in the decimation circuit 15 in accordance with this sampling frequency FRS to perform resampling with the sampling frequency adapted to the required band width. Thus, A/D conversion is successively executed in accordance with the use band of an input signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a signal processing device that performs various signal processing using digital signals obtained by converting analog signals such as voice and various acoustic signals.

2. Description of the Related Art In recent years, with advances in semiconductor technology, devices that process audio signals and the like using digital signals have been put into practical use. These devices require an AD@DA conversion device that converts analog signals and digital signals. Then, signal processing is performed on the digitized signal. The AD converter determines the highest frequency of the signal to be digitized, and uses this value and the sampling theorem to uniquely determine the sampling frequency at which the signal is digitized.

A signal processing device using a conventional AD/DA converter will be explained below.

FIG. 4 shows the configuration of a signal processing device using a conventional AD/DA converter, where 41 is an AD converter, and 42 is an AD converter.
4 is a signal processing device, and 43 is a DA converter.

The operation of the signal processing device configured as described above will be described below.

An input analog signal such as a voice or an acoustic signal is converted into a digital signal by an AD converter 41. At this time, the sampling frequency for sampling is determined by the highest frequency of the input signal, and is not changed during signal processing. next.

The digital signal converted by the AD conversion device 41 is subjected to various processing in the signal processing device 42. The digital signal processed by the signal processing device 42 is then transferred to the DA converter 43.
is converted to an analog signal and output. The sampling frequency during this DA conversion is also generally the same as the sampling frequency during AD conversion, and is not changed.

Problems to be Solved by the Invention In the above-mentioned conventional configuration, signal processing is performed while the sampling frequency of the AD/DA converter is kept at a constant value. The sampling frequency is determined by the effective band of the input analog signal. For example, in the case of a telephone audio signal processing device, the effective band is 0.3 to 3.4 kHz, and the sampling frequency is 8 kHz, while for compact discs, the effective band is several 2 to 20 kHz, and the sampling frequency is 44. It is 1kHz. In these conventional signal processing devices, signal processing is performed at all sampling frequencies having a fixed value based on the highest frequency that can be input. In other words, even when recording and playing back audio from a compact disc, the signal is processed at the same sampling frequency as the audio signal. On the other hand, in an audio signal processing device, processing of an acoustic signal has a narrow band, which causes problems. Furthermore, when a signal containing both voice and acoustic signals is stored as a digital signal, the sampling frequency needs to match the acoustic signal with a wider band.

However, if the audio is sampled at the same sampling frequency as the acoustic signal when recording the audio, a large amount of time will be wasted in the time required for signal processing and in the storage capacity for storing data.

The present invention improves the configuration of the conventional AD/DA conversion device and signal processing device, and has a function of programmable sampling frequency selection or selecting an optimal sampling frequency according to a signal band included in a predetermined time width,
It is an object of the present invention to provide an excellent sampling frequency selective shadow signal processing device having a configuration for performing signal processing at the sampling frequency.

Means for Solving the Problems The sampling frequency selection type AD conversion device of the present invention has a configuration including a frequency component calculation circuit for calculating frequency components, a sampling frequency selection circuit, and a decimator 8-f circuit. . In addition, the sampling frequency selective DA converter is
The configuration includes an interpolation ratio calculation circuit and an interpolation circuit. The sampling frequency selective shadow signal processing device has a configuration including a sampling frequency selective AD converter and a sampling frequency selective DA converter.

Operation With this configuration, the sampling frequency selective AD converter calculates the upper limit value of the required band by the frequency component calculation circuit, or manually sets the sampling frequency F' to an appropriate value to perform resampling. By selectively determining t+s and decimating it using a decimation circuit according to this sampling frequency FRS, resampling is performed at a sampling frequency that matches the required bandwidth. This allows AD conversion to be successively adapted to the usage band of the input signal.

In a sampling frequency selective DA converter, in order to interpolate a signal up to a predetermined sampling frequency according to the input sampling frequency, an interpolation ratio calculation circuit first calculates the interpolation ratio, and then an interpolation circuit calculates the interpolation ratio. Interpolate the signal. Thereby, the digital signal AD-converted by the sampling frequency selective AD converter can be converted into an analog signal.

In addition, in the sampling frequency selective shadow signal processing device, the digital signal whose sampling period has been selectively changed by the sampling frequency selective AD converter is processed by the digital signal processing circuit, and the digital signal is processed by the sampling frequency selective AD converter. D by adapting to the sampling frequency that changes every predetermined number of samples.
A conversion is possible.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of a sampling frequency selective AD converter according to a first embodiment of the present invention. In FIG. 1, 11 is an analog low-pass filter, 12 is an AD converter, 13 is a frequency component calculation circuit, 14 is a sampling frequency selection circuit, 15 is a decimator 8 filter, and 16 is a digital low-pass filter.

The operation of the sampling frequency selective AD converter of this embodiment configured as described above will be described below.

An analog input signal whose band fluctuates is band-limited by an analog low-pass filter 11 to only a band below FCL in consideration of the highest input frequency component FcL. A.D.
The converter 12 samples the output signal of the analog low-pass filter 11 at a sampling frequency F8 satisfying F9>2FCL and converts it into a digital signal. The frequency component calculation circuit 13 receives the digital signal converted by the AD converter 12 as input, and calculates its frequency component by using a predetermined number of consecutive samples as one frame. The sampling frequency selection circuit 14 determines the sampling frequency FRS for resampling, taking into account the highest frequency component included in the frame based on the result of the calculation by the frequency component calculation circuit 13. Decimer-207 circuit 15 is A
At the sampling frequency F8 which is the output of the D converter 12 →
The scrambled digital data is thinned out according to the sampling frequency FRS, thereby downsampling the data. For example, there are the following techniques for downsampling. r R,E
, Croehl-ere and L.R., Rabln.
er, ”Interpolatlon and De
ciocation of Digital Slgn
``Proceedings of the
IEEE, Vol. G9. No, 3. Mar, 19
The downsampled data is input to a digital low-pass filter 1θ, Filtering for band limitation is performed according to the sampling frequency FRS.Here, the digital low-pass filter 16 has a sampling frequency FRS.
Calculated in synchronization with RI+, cutoff frequency is FRs
is set to less than half of This sampling frequency selective AD
The output of the conversion device is the sampling frequency pRs after downsampling and the digital low-pass filter 16.
and the sample output downsampled at the sampling frequency FRS, which is the output of . Here, it is assumed that the output is output at frame 11i. The sampling frequency FRS may be changed on a frame-by-frame basis.
The number of sampling data in one frame changes depending on the sampling frequency hs.

Here, the sampling frequency FRS is
As described in Section 1, the determination may be made based on band information provided externally.

As described above, according to this implementation order, by providing the sampling frequency selection circuit, it is possible to selectively change the sampling frequency according to the band of the input signal.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows the configuration of a sampling frequency selective AD converter according to a second embodiment of the present invention. In FIG. 2, 21 is an interpolation ratio calculation circuit, 22 is an interpolation ratio calculation circuit, 23 is a digital low-pass filter, and 24 is an interpolation ratio calculation circuit.
is DA, I exchange! , a 25-channel analog low-pass filter.

The operation of the sampling frequency selective DA converter of this embodiment configured as described above will be described below.

This embodiment takes as input the sampling frequency selected according to the band and its sampling data output from the sampling frequency selective AD converter according to claim 1 or 2, and converts this into an analog signal. It is something to do.

First, the interpolation ratio calculation circuit 21 calculates an interpolation ratio according to the ratio between the input sampling frequency FIN information and the sampling frequency FOLlT used for later conversion into an analog signal. The interpolation circuit 28 inserts zeros as data in order to interpolate the input sample data according to the interpolation ratio calculated by the interpolation ratio calculation circuit 21. The digital low-pass filter 23 is
A cutoff frequency is set according to the sampling period pout of the post-DA converter 24, and the data captured by the zero output from the intervore margin circuit 22 is filtered. This digital low pass filter 2
The output data No. 3 is obtained by converting the sample data that is the input of this embodiment into sample data having the same sampling frequency FOLI7. That is, the downsampled data is upsampled among the sample data that has been AD converted with various 77' IJ song wave numbers in units of frames. Regarding this upsampling technique, for example, the above-mentioned literature can be mentioned. Next, the DA converter 24 uses the sampling frequency FOU which is the output of the digital low-pass filter 23.
The data of T is DA converted and converted into an analog signal. The analog low-pass filter 25 removes unnecessary frequency components from the analog signal output from the DA converter 24.

As described above, according to this embodiment, sample data sampled at various sampling frequencies can be converted into analog signals by providing the interpolation ratio calculation circuit and the interpolation ratio calculation circuit.

A third embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows the configuration of a sampling frequency selective shadow signal processing apparatus in a third embodiment of the present invention. In FIG. 3, 31 is a sampling frequency selective AD converter, 32 is a signal processing device, 33 is a sampling frequency selective DA converter, and 34 is a semiconductor memory.

The operation of the sampling frequency selective shadow signal processing device of this embodiment configured as described above will be described below.

An analog input signal whose band fluctuates in a relatively long period is AD converted by the sampling frequency selective AD converter 31 at a sampling frequency that takes into consideration the effective bandwidth.

As shown in the first embodiment, the sample data AD-converted by the sampling frequency selective AD converter 31 is
The sampling frequency is changed as appropriate depending on the frequency components included in the input signal. The signal processing device 32 performs signal processing such as level control and sound detection on input sample data of various sampling frequencies, and controls data input/output to the semiconductor memory 34 . The semiconductor memory 34 is a medium that stores information about the signal processing device 32, sampling frequency, and sample data. The sampling frequency selective DA converter 33 converts the sampling frequency data and sample data read from the semiconductor memory 34 by the signal processing device 32 into analog signals. As shown in the second embodiment, this sampling frequency selective DA converter performs DA conversion on sample data that has been AD converted at various sampling periods.

As mentioned above, according to this implementation order, sampling frequency selection type A
By providing a D conversion device and a sampling frequency selective DA conversion device, the sampling frequency can be selectively changed according to the band of the input signal, and this can be used in a signal processing device including a storage medium such as a semiconductor memory. By combining it with , it is possible to reduce the storage capacity.

Effects of the Invention The present invention can selectively change the sampling frequency on a frame-by-frame basis when long-term frequency components included in an input signal change over a long time period, and can be sampled in a relatively narrow range such as audio. Even when sampling wide-band signals such as music learning signals, you can always obtain sample data sampled at the optimal sampling frequency, and perform optimal signal processing that eliminates redundancy related to the sampling frequency. It is possible to realize this. Another advantage is that when performing signal processing that requires a long calculation time, the processing delay can be shortened by adaptively lowering the sampling frequency.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a configuration diagram of a sampling frequency selective AD converter according to an embodiment of the present invention, and FIG. 2 is a configuration diagram of a sampling frequency selective AD converter according to an embodiment of the present invention. FIG. 3 is a block diagram of a sampling frequency selective shadow signal processing device according to an embodiment of the present invention, and FIG. 4 is a block diagram of a conventional signal processing device. 11...Analog low-pass filter, 12...AD
Converter, 13... Frequency component calculation circuit, 14... Sampling frequency selection circuit, 15... Deciturf 8f circuit, 16... Digital low-pass filter, 21.
...Interpolation ratio calculation circuit, 22...Interbothee 26
F circuit, 23...Digital Rono 5 size filter,
24... DA variable FAi, 25... Analog low-pass filter, 31... Sampling frequency selection type AD conversion device, 32... Signal processing device, 33... Sampling frequency selection type DA conversion device, 34... semiconductor memory, 41...
- AD conversion device, 42... signal processing device, 43...
DA converter.

Claims (4)

[Claims] (1) Use of an analog low-pass filter that band-limits the highest frequency component of an input signal to F_C_L, and an AD converter that converts the output signal of the low-pass filter to a digital signal at a sampling frequency F_B that is more than twice F_C_L. sampling frequency F_R_ for resampling the output signal of the AD converter according to the band
a sampling frequency selection circuit that can selectively set S; a decimation circuit that appropriately thins out the output signal of the AD converter according to the sampling frequency F_R_S set by the sampling frequency selection circuit; a digital low-pass filter for band-limiting according to F_R_S determined by the sampling frequency setting circuit in order to remove anomalous phenomena, and outputting a resampled digital signal and a sampling frequency F_R_S used for resampling; Frequency selective AD converter. (2) an analog low-pass filter that band-limits the highest frequency component of an input signal to F_C_L; and an AD converter that converts the output signal of the low-pass filter into a digital signal at a sampling frequency F_B that is twice or more F_C_L; a frequency component calculation circuit for calculating frequency components included in a predetermined number of continuous samples of a digital signal output from an AD converter; and a digital signal output from the AD converter according to an output signal of the frequency component calculation circuit. Sampling frequency F_R to resample
_S; a decimation circuit for appropriately thinning out the digital signal that is the output of the AD converter according to the sampling frequency F_R_S determined by the sampling frequency selection circuit; and a decimation circuit for appropriately thinning out the digital signal that is the output of the AD converter; F_R_ determined by the sampling frequency setting circuit to eliminate the phenomenon.
A sampling frequency selective AD converter includes a digital low-pass filter for band limiting according to S, and outputs a resampled digital signal and a sampling frequency F_R_S used for resampling. (3) Sampling frequency information F_I_N that is changed every predetermined number of samples and the sampling frequency F_I
an interpolation ratio calculation circuit that receives a digital signal sampled at _N as an input signal and determines an interpolation ratio according to a ratio between the sampling frequency F_I_N and a set sampling frequency F_O_U_T; an interpolation circuit for interpolating an input digital signal; a digital low-pass filter for band-limiting the interpolated digital signal output from the interpolation circuit with a bandwidth corresponding to the sampling frequency F_O_U_T; The output is set to the sampling frequency F_O
A sampling frequency selection type D equipped with a DA converter for converting into an analog signal at _U_T and an analog low-pass filter for removing unnecessary bands of the output signal of the DA converter.
A conversion device. (4) Using a sampling frequency selective AD converter that can select a sampling frequency according to the frequency component of an input signal, and information on the digital signal and sampling frequency that are output from the sampling frequency selective AD converter. A sampling frequency system comprising: a digital signal processing device that performs signal processing; and a sampling frequency selective DA converter that receives a digital signal output from the digital signal processing device and sampling frequency information and converts it into an analog signal. Selective signal processing device.