JP3124331B2 - Voice squelch circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice squelch circuit used in a radio receiver, which determines whether or not a received signal is a voice signal, and outputs the result.

[0002]

2. Description of the Related Art FIG. 2 shows a system diagram of a general receiver.
In the figure, 21 is an antenna, 22 is a high-frequency amplifier (R
FA), 23 is a mixing section (MIX), 24 is a local oscillation section (OSC), 25 is an intermediate frequency amplification section (IFA), 26 is a detector (DET), 27 is an audio squelch circuit, and 28 is a speaker. In this figure, the signal received by the antenna 21 is different from the local oscillation frequency of the local oscillator 24 and the mixer 23.
Are converted into an intermediate frequency, amplified, detected by a detector 26, and output to a speaker 28 in the case of voice by a voice squelch circuit 27.

FIG. 3 shows an example of the configuration of the conventional voice squelch circuit 27 used in FIG. Reference numeral 31 denotes a band-pass filter (BPF) for extracting a signal component, and 32 denotes a filter (FIL) for extracting a noise component. A low-pass filter or a high-pass filter is used. 33,3
Reference numeral 4 denotes an amplifier (AMP) for amplifying the outputs from the BPF 31 and the FIL 32 to required levels, respectively. Reference numeral 35 denotes a comparator for comparing the outputs from the amplifiers 33 and 34. 3
Reference numeral 6 denotes a switch (SW) for turning on / off the detected demodulated signal.

[0004] The input signal from the detector 26 is input to the BPF 31 and the FIL 32, where the BPF 31 extracts a signal component and the FIL 32 extracts a noise component. These outputs are amplified to required outputs by the amplifiers 33 and 34, respectively, and the comparator 35 compares the levels of the signal component and the noise component. As a result of this comparison, when the signal component is large, SW3
6, the input signal is output to the speaker 28 as it is, but when the noise component is large, the SW 36 is controlled so that the input signal is not output.

[0005]

However, such a conventional circuit is based on the comparison between the signal and noise levels, and does not detect whether or not the input signal is a voice. Therefore, a signal having a frequency component similar to that of the audio band, for example, a telegraph wave, FSK (Frequency Shift K)
eyeing) It cannot operate correctly as a voice squelch circuit against interference and interference of signals and the like. An object of the present invention is to eliminate the above-mentioned drawbacks, and to determine whether or not an input signal is a voice and output the result, thereby ensuring a squelch operation of blocking signals other than voice and outputting only voice. It is another object of the present invention to provide a voice squelch circuit which can be performed at a time.

[0006]

A voice squelch circuit according to the present invention comprises: a pitch detector for detecting a demodulation output of a radio receiver as an input signal; analyzing the input signal as voice; and detecting a pitch frequency; A determination circuit for outputting a logic "1" if the pitch frequency from the input signal is within a predetermined audio frequency range; a low frequency detector for extracting energy of a low frequency spectrum component of an audio band from the input signal; A high-frequency detector for extracting the energy of the high-frequency spectrum component of the voice band from the output signal, and a comparator for comparing the outputs of the low-frequency detector and the high-frequency detector and outputting a logical "1" when the output of the low-frequency detector is large. An AND circuit for calculating the logical product of the output of the judgment circuit and the output of the comparator; averaging the output of the AND circuit for a predetermined time to judge whether or not the sound is a sound, and outputting the result; It is characterized in further comprising an integration determination circuit.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a pitch detector for detecting a pitch frequency which is a feature of a voice, and a method based on waveform processing, correlation processing or spectrum processing is used for the detection method. Reference numeral 4 denotes a determination circuit for determining whether or not the pitch frequency obtained by the pitch detector 1 is within a predetermined range (for example, 50 to 300 Hz considering a male voice as 50 to 200 Hz and a female voice as 80 to 300 Hz). Reference numeral 2 denotes a low-frequency detector that detects energy distributed in a low-frequency region, and uses a low-pass filter. 3
Is a high-frequency detector for detecting energy distributed in a high-frequency region, and uses a high-pass filter. Reference numeral 5 denotes a comparator for comparing the output levels of the low frequency detector 2 and the high frequency detector 3. Reference numeral 6 denotes a logical product (AND) circuit. This output indicates a condition match only when the output of the determination circuit 4 is within a specified range and the output of the comparator 5 is determined to be logic "1".
Reference numeral 7 denotes an integration determination circuit for performing determination for a certain period of time, and is used for performing an averaging process. 8 is a changeover switch (S
W), an operation is performed to determine whether or not to output the input signal a to the speaker 28.

Next, the operation will be described. The input signal a is input to the changeover switch 8 and simultaneously to the pitch detector 1, the low frequency detector 2, and the high frequency detector 3. The pitch detector 1 detects a pitch frequency, and a decision circuit 4
Then, it is determined whether or not the frequency range is in the range of, for example, 50 to 400 Hz. If the condition is satisfied, a logical value “1” is output. On the other hand, the low frequency detector 2 calculates the energy of the low frequency signal (900 Hz or less) of the audio spectrum, and the high frequency detector 3 calculates the energy of the high frequency signal (900 Hz or more) of the audio spectrum. Is entered. The comparator 5 compares the low band energy with the high band energy, and outputs a logical value "1" if the low band energy is large. In the AND circuit 6, the judgment circuit 4
Is ANDed with the output of the comparator 5, and when both are "1", a logic "1" is output. In the integration judgment circuit 7, AND
The judgment output from the circuit is averaged for a certain period of time,
It is determined whether or not the signal is an audio signal, and a signal indicating one of them is output. The changeover switch 8 connects the input signal a to the speaker 28 when it is determined that the signal is an audio signal. Note that the detection method of the pitch detector 1 includes waveform processing, correlation processing, spectrum processing, and the like, and the method of obtaining the pitch frequency is as follows. In the case of waveform processing, the peak value of the input waveform is detected by a peak detector, the time between the peak values is obtained, and the average value of those times is processed. In the case of correlation processing a. The autocorrelation function of the input waveform is obtained and its cycle is obtained. B. LPC (linear predictive) called linear predictive analysis for input waveforms
coding) analysis to determine a correlation function of the residual signal. Since the correlation function shows a large correlation value at an integral multiple of the fundamental period, it is obtained from this result. In the case of spectrum processing The so-called cepstum obtained by taking the logarithm of the power spectrum of the input signal and performing the inverse Fourier transform is separated into portions showing the envelope of the spectrum and the fine structure of the spectrum. It can be obtained by obtaining the interval between the peak values of the high quefrency (time) portion indicating the fine structure of the spectrum.

[0009]

According to the present invention, the following effects can be obtained. (1) The switching of performing the squelch operation of audio with or without a signal can be reliably performed by determining whether or not the signal is an audio signal. (2) In a wireless system, it is particularly effective for a squelch circuit of a radio device in a short wave band where interference and interference are frequent.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a receiver system diagram.

FIG. 3 is a block diagram illustrating a conventional receiving circuit example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pitch detector 2 Low frequency detector 3 High frequency detector 4 Judgment circuit 5 Comparator 6 AND circuit 7 Integral judgment circuit 8 Switch 21 Antenna 22 High frequency amplification part 23 Mixing part 24 Local oscillation part 25 Intermediate frequency amplification part 26 Detector 27 Voice squelch circuit 28 speaker 31 BPF 32 filter 33,34 amplifier 35 comparator 36 switch

Claims (1)

(57) [Claims] 1. A pitch detector for detecting a demodulation output of a radio receiver as an input signal and analyzing a voice of the input signal to detect a pitch frequency, wherein a pitch frequency from the pitch detector is within a predetermined voice frequency range. A determination circuit that outputs a logic "1" if present; a low-frequency detector that extracts the energy of a low-frequency spectrum component in the audio band from the input signal; and extracts the energy of a high-frequency spectrum component in the audio band from the input signal. A high-frequency detector, a comparator that compares the outputs of the low-frequency detector and the high-frequency detector and outputs a logic “1” when the output of the low-frequency detector is large, and an output of the determination circuit and the comparator. A voice squelch comprising: an AND circuit for calculating a logical product of the output; and an integration determining circuit for averaging the output of the AND circuit for a predetermined time to determine whether or not the voice is voice and outputting the result. circuit.