JPH0367397B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waveform encoding device that is capable of varying the clock rate used to encode and transmit information signals such as audio signals and video signals, and particularly has a simple configuration and good performance. This makes it possible to vary the clock rate, lower the average bit rate, and improve signal transmission quality.

2. Description of the Related Art Conventionally, there is a waveform encoding device as shown in FIG. 1 which has a variable clock rate.
That is, 1 is a waveform encoding device that constitutes a transmitting device;
2 is a decoding device that constitutes a receiving device; 3a and 3b;
indicate the respective transmission paths. This waveform encoding device 1 converts the information signal supplied to the information signal input terminal 1a into a cut-off frequency _fV that is half the frequency of the clock signal of the variable clock generator 7, which will be described later, using a control signal _CS , which will be described later. The effective frequency bandwidth of the information signal supplied to the information signal input terminal 1a is supplied to the adaptive delta modulator 5 constituting the waveform encoder via the variable low-pass filter 4 configured to be controlled. Bandwidth detection circuit 6
A DC voltage control signal C _S corresponding to the effective frequency bandwidth of the input information signal is obtained at the output side of this bandwidth detection circuit 6, and a control signal obtained at the output side of this bandwidth detection circuit 6 is supplied to C _S is supplied to the oscillation frequency control terminal of a variable clock generator 7 constituted by a voltage variable oscillator circuit, and this control signal C _S is supplied to the cut-off frequency control terminal of the variable low-pass filter 4. The cutoff frequency _fV of the variable clock generator 7 is controlled, and the clock signal obtained at the output side of the variable clock generator 7 is supplied to the adaptive delta modulator 5, and the adaptive delta modulator 5 performs sampling, etc. using this clock signal. , and encoding is performed using this clock signal. The delta modulated signal obtained at the output terminal 5a of the adaptive delta modulator 5 of this conventional waveform encoding device 1 and the output terminal 6a of the bandwidth detection circuit 6
The control signal C _S obtained in the above is transmitted to the decoding device 2 via the transmission lines 3a and 3b, and the delta modulation signal obtained at the information signal input terminal 2a of the decoding device 2 is supplied to the adaptive delta modulation decoder 8. The demodulated signal obtained at the output side of the adaptive delta modulation decoder 8 is supplied to the demodulated signal output terminal 9a via the variable low-pass filter 9, and the control signal obtained at the control signal input terminal 2b of the decoding device 2 is supplied to the demodulated signal output terminal 9a. The signal C _S is supplied to a variable clock generator 10 constituted by a voltage variable oscillator circuit which supplies the clock signal obtained at its output to an adaptive delta modulation decoder 8, and this control signal C _S is passed through a variable low-pass filter 9. A cutoff frequency _fV of the variable low-pass filter 9 is supplied to a control terminal for controlling the cutoff frequency fV, so that the cutoff frequency _fV of the variable low-pass filter 9 is made to be half the frequency of the clock signal of the variable clock generator 10.

In the conventional waveform encoding device 1 and decoding device 2, the frequency band of the input information signal is detected to determine the oscillation frequency of the variable clock generators 7 and 10 and the cutoff frequency _fV of the variable low-pass filters 4 and 9. Therefore, when there is no high-frequency component in the input information signal, the oscillation frequency of the variable clock generators 7 and 10 is lowered, and the average bit rate can be lowered, thereby improving the signal transmission quality. The cutoff frequency _fV of the variable low-pass filters 4 and 9 is also lowered, and quantization noise can be reduced.

However, the conventional waveform encoding device 1 and decoding device 2 have a transmission method in which the control signal C _S obtained at the output side of the bandwidth detection circuit 6 is transmitted outside the transmission path 3a of the delta modulated signal, which is the main information signal. There is a disadvantage that the circuit 3b is required, which complicates the configuration, and that the bandwidth detection circuit 6 requires an FFT (Fast Fourier Transformer) or the like, which complicates the configuration.

In view of these points, the present invention has been developed to enable good clock rate variation with a simple configuration, to lower the average bit rate, and to improve signal transmission quality.

An embodiment of the waveform encoding device of the present invention will be described below with reference to FIG. In FIG. 2, parts corresponding to those in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

In this example, the information signal supplied to the information signal input terminal 1a is supplied via a variable low-pass filter 4 to an adaptive delta modulator 5 constituting a waveform encoder. In this example, this adaptive delta modulator 5
A local decoding section 5b is provided in a part of the decoding section. This local decoding section 5b decodes again the delta modulation signal encoded in the adaptive delta modulator 5, and the output side of this local decoding section 5b is connected to the adaptive delta modulation decoder 8 of the decoding device 2, which will be described later. This is done so that a demodulated signal similar to the output signal is obtained. This local decoding section 5b
The demodulated signal obtained at the output side of the filter is supplied to the high-pass filter 11. The cut-off frequency _fV of this high-pass filter 11 is set to 1.5 kHz, for example, when the demodulated signal is an audio signal, and this signal of 1.5 kHz or more is supplied to the level detection circuit 12. The level of the signal that has passed is detected, and a DC voltage corresponding to the level of this high-frequency signal is obtained. This allows us to know the amount of high-frequency components. It can be considered as width. The level detection signal of this level detection circuit 12 is supplied as a control signal _CS to the oscillation frequency control terminal of a variable clock generator 7 constituted by a voltage variable oscillation circuit, and the frequency of the clock signal generated by this variable clock generator 7 is The level detection circuit 1
The level detection signal of this level detection circuit 12 is supplied as a control signal C _S to the cut-off frequency control terminal of the variable low-pass filter 4, and this control signal C _S The cutoff frequency _fV of the filter 4 is made to be half the frequency of the clock signal of the variable clock generator 7. Further, the clock signal of the variable clock generator 7 is supplied to the adaptive delta modulator 5, and the adaptive delta modulator 5 delta modulates the input information signal using the clock signal as a reference. The delta modulated signal obtained at the output terminal 5a of this adaptive delta modulator 5 is transmitted to the decoding device 2 via the transmission line 3, and the delta modulated signal obtained at the information signal input terminal 2a of this decoding device 2 is adaptively delta modulated. The signal is supplied to a decoder 8 for demodulation, and the demodulated signal obtained at the output side of the adaptive delta modulation decoder 8 is supplied via a variable low-pass filter 9 to a demodulated signal output terminal 9a.

Further, the demodulated signal obtained at the output side of the adaptive delta modulation decoder 8 is supplied to a high-pass filter 13 configured similarly to the high-pass filter 11 and which passes signals with a frequency of 1.5 kHz or higher, for example, and the output signal of this high-pass filter 13 is is supplied to a level detection circuit 14 configured similarly to the level detection circuit 12, and this level detection circuit 14 detects the level of the signal that has passed through the high-pass filter 13, and detects the level of the high-frequency signal according to the level of the high-pass filter 13. By obtaining a DC voltage, it is possible to know the amount of high-frequency components, and this can be regarded as the effective frequency band of an input information signal, such as an audio signal. The level detection signal of the level detection circuit 14 is supplied as a control signal _CS to the oscillation frequency control terminal of the variable clock generator 10 constituted by a voltage variable oscillation circuit, and the frequency of the clock signal generated by the variable clock generator 10 is controlled. The level detection signal of the level detection circuit 14 is used as a control signal C _S to increase the level according to the detection level of the level detection circuit 14, and the variable low-pass filter 9
This control signal C _S is used to set the cut-off frequency f _V of the variable low-pass filter 9 to half the frequency of the clock signal of the variable clock generator 10 . The clock signal of the variable clock generator 10 is also supplied to the adaptive delta modulation decoder 8, and the adaptive delta modulation decoder 8 demodulates the delta modulation signal using this clock signal as a reference.

The waveform encoding device 1 and decoding device 2 shown in FIG.
In this case, the frequency band of the input information signal is detected as in the example in _FIG . When there is no high-frequency component in the information signal, the oscillation frequency of the variable clock generators 7 and 10 is lowered, and the average bit rate can be lowered. The cutoff frequency f _V also becomes lower,
Quantization noise can be reduced. Furthermore, in this example, the frequency band of the demodulated signal demodulated by the decoders 5b and 8 is detected by the high-pass filters 11 and 13 and the level detection circuits 12 and 14, so the detection circuit for detecting this frequency band is simple. In addition, there is an advantage that a special transmission path for transmitting the control signal C _S is not required, and the configuration is simpler.

Although the variable low-pass filter 4 was provided in the above embodiment, the adaptive delta modulator 5 also has the effect of a variable low-pass filter, so the variable low-pass filter 4 can be omitted. Further, the present invention is not limited to the above-described embodiments, and it goes without saying that various other configurations may be adopted without departing from the gist of the present invention.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an example of a conventional waveform encoding device, and FIG. 2 is a configuration diagram showing an embodiment of the waveform encoding device of the present invention. 1a is an information input terminal, 4 is a variable low-pass filter, 5 is an adaptive delta modulator, 5a is an output terminal, 5
b is a local decoder, 7 is a variable clock generator, 11
1 is a high-pass filter, and 12 is a level detection circuit.

Claims (1)

[Scope of Claims] 1. Waveform encoding means having a local decoding unit that encodes an input signal and transmits the encoded signal, and decodes the encoded signal; and a clock signal to the waveform encoding means. a high-pass filter to which the output signal of the local decoding section of the waveform encoding means is supplied; detecting the level of the high-frequency component obtained by the high-pass filter; 1. A waveform encoding device comprising: level detection means for outputting a control signal; and the frequency of the clock signal of the variable clock generation means is controlled by the control signal obtained from the level detection means.