JPH0415525A - Single tone detector - Google Patents

Abstract

PURPOSE:To improve the decision rate for deciding a single tone or not even in the case an input signal-to-noise ratio is small by comparing a coefficient of a filter and a threshold by a deciding device and detecting whether an input digital signal is a single tone or not. CONSTITUTION:A sound part and a no-sound part of an inputted digital signal are detected by a signal-to-noise ratio calculating circuit 3, and a ratio of signal power of the sound part and the no-sound part is calculated. An initial value corresponding to an output of the circuit 3 is selected by an initial value selecting circuit 4, and inputted to a secondary adaptive FIR filter 2. The filter 2 predicts the inputted digital signal by a digital signal train inputted in the past, and also, sets an output of the circuit 4 as an initial value of a coefficient of the filter only when the circuit 3 outputs a fact to be the sound part from the no-sound part. A threshold selecting circuit 5 selects a threshold corresponding to a signal-to-noise ratio being an output of the circuit 3, and by a deciding device 6, a coefficient of the filter and a variable threshold being an output of the circuit 5 are compared, and a single tone or not is decided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a single tone detector for detecting a single tone, which is a sine wave of a single frequency.

[Conventional technology]

FIG. 4 is a block diagram showing an example of a conventional single tone detector, which includes a plurality of bandpass filters, a determiner, and a detection circuit.

Detection of a single tone is performed by comparing the ratio of the amplitude values of the input signal and the output of the bandpass filter with a narrow passband with a preset threshold value. When the ratio of amplitude values is above the threshold,
Since the input signal component is estimated to include only the passband signal component and not other band signal components, it can be determined that it is a single tone.

The input digital signal input from the terminal 40 is input to band pass filters 41, 43, 45, to 47, the number of which is determined depending on the number of single tones to be detected. Bandpass filter 41 outputs only the frequency components to be detected. The determiner 42 compares the output of the bandpass filter 41 and the input digital signal, and sets the ratio of the amplitude values of the two to a preset threshold close to 1, for example, O.
95) In the above cases, it is determined that the tone is a single tone, and '1'' is output to the detection circuit 49. When the ratio of both amplitude values is smaller than the above-mentioned threshold value, it is determined that it is not a single tone, and the four detection circuits are output. In the same way, the band pass filter 43 and the judge 44, the band pass filter 45 and the judge 46, and the band pass filter 47 and the judge 4
8 performs detection of different bands. In the four detection circuits, determiners 42.44.4.6. When any one of the outputs .about.48 is 1.degree.', it is determined to be a single tone, and a single tone detection signal is output from the output terminal 50.

[Problem to be solved by the invention]

In the conventional single tone detector described above, in order to detect a single tone in two bands, - sets of bandpass filters and determiners are required.

Therefore, the same number of bandpass filters and determiners as the number of single tones to be detected were required. In particular, when the number of single tones to be detected increases, the circuit scale increases, and when implemented using a general-purpose processor, the amount of program calculation increases.

In addition, when the signal-to-noise ratio of the signal power of the active part and the signal power of the silent part such as background white noise becomes small, the amplitude ratio of the input signal and the output signal of the band-pass filter becomes small due to the influence of the noise, making it difficult to make accurate judgments. The problem was that it was difficult.

[Means to solve the problem]

The single tone detector of the first invention detects whether or not an input digital signal is a single tone. A signal-to-noise ratio calculation circuit that calculates the ratio of signal power between a sound part and a silent part, an initial value selection circuit that selects an initial value according to the output of this signal-to-noise ratio calculation circuit, and an input digital signal. is predicted from a digital signal sequence input in the past, and only when the signal-to-noise ratio calculation circuit outputs a sound part from a silent part, the output of the initial value selection circuit is set as the initial value of the coefficient of the filter. a second-order adaptive FIR filter; a threshold selection circuit that selects a threshold according to the signal-to-noise ratio that is an output of the signal-to-noise ratio calculation circuit; and coefficients of the second-order adaptive FIR filter and the threshold selection. It is characterized in that it is comprised of a determiner that compares the variable threshold value that is the output of the circuit and determines whether or not it is a single tone.

The single tone detector of the second invention detects whether or not an input digital signal is a single tone. A signal-to-noise ratio calculation circuit that calculates the ratio of signal power between a sound part and a silent part, an initial value selection circuit that selects an initial value according to the output of this signal-to-noise ratio calculation circuit, and an input digital signal. is predicted from a digital signal sequence input in the past, and only when the signal-to-noise ratio calculation circuit outputs a sound part from a silent part, the output of the initial value selection circuit is set as the initial value of the coefficient of the filter. a second-order adaptive FIR filter; a threshold selection circuit that selects a threshold according to the signal-to-noise ratio that is an output of the signal-to-noise ratio calculation circuit; and coefficients of the second-order adaptive FIR filter and the threshold selection. a first judger that compares a variable threshold value that is the output of the circuit and judges whether or not it is a single tone; a low-pass filter that removes high frequency components of the output of the first judger; It is characterized by comprising a second determiner that compares the output of the low-pass filter with a predetermined fixed threshold value to determine whether or not it is a single tone.

The signal-to-noise ratio calculation circuit also includes a sound detector that detects a sound part and a silent part of the input digital signal, and a sound detector that detects the sound part and the silent part of the input digital signal. a delay circuit that delays a sample time; a signal power calculation circuit that calculates the power of an output signal of the delay circuit; and a signal power calculation circuit that calculates the signal power when the sound detector outputs a sound part from a silent part. A holding circuit that holds the calculated power value as the calculated value of the silent part signal power, and a signal-to-noise ratio between the calculated value of the sound part signal power of the signal power calculation circuit and the calculated silent part signal power value that is the output of this holding circuit. It is characterized by comprising a comparison calculation circuit that calculates a ratio.

[Effect]

In the present invention, a second-order adaptive F
Use an IR filter. When the input digital signal is a sine wave, the second-order filter coefficient a2 converges to a certain value, and the determiner compares the filter coefficient a2 with the threshold value to determine if the input digital signal is a single wave. Detect whether it is a tone or not. In addition, when the input signal changes from a silent state to a sound state in the signal-to-noise ratio calculation circuit, the initial value of the coefficient a2 of the filter is determined according to the signal-to-noise ratio obtained from the signal power ratio of the sound part and the silent part. The input signal-to-noise ratio can be adjusted by changing the threshold value used to determine whether a single tone is present or not according to the signal-to-noise ratio determined by the signal power ratio between the sound part and the silent part. Even if it is small, the determination rate of whether or not it is a single tone can be further improved. Furthermore, in the second invention,
By inputting the output of the determiner into a low-pass filter and comparing it with a predetermined threshold, it is possible to remove incorrect determination portions that occur in a short period of time due to local noise.

〔Example〕

Next, the first. The second invention will be explained with reference to FIGS. 1 to 3.

Figures 1 and 2 are respectively 1. FIG. 7 is a block diagram of an embodiment of a single tone detector according to the second invention.

First, in FIG. 1, 1 is an input terminal, 2 is a second-order adaptive FIR filter, 3 is a signal-to-noise ratio calculation circuit, 4 is an initial value selection circuit, 5 is a threshold selection circuit, 6 is a judger, 10 is the output terminal. The second-order adaptive FIR filter 2 includes a unit delay circuit 21 . Unit delay circuit 221 multiplier 23. Filter coefficient modification unit 241 multiplier 25. Filter coefficient correction unit 2
6 adder 27. It is composed of a subtracter 28.

A digital signal is input to the unit delay circuit 21 and the subtracter 28. The coronation delay circuit 21 delays the input digital signal by one sample time and outputs the delayed signal.The output thereof is input to the unit delay circuit 22 and the multiplier 23. In the multiplier 23,
The output of the unit delay circuit 2] is multiplied by the output a1 of the filter coefficient correction section 24. On the other hand, the unit delay circuit 22
The output of is input to the multiplier 25, and the filter coefficient correction unit 2
Multiplication with the output a2 of 6 is performed. Here, only when the input signal changes from a silent state to a sound state in the signal-to-noise ratio calculation step ii'83 to be described later, the initial value selection circuit 4
The initial value selected in is output a2 of the filter coefficient correction unit 26.
be the initial value.

Regarding the initial value, the optimum value differs depending on the signal-to-noise ratio determined by the line condition. The initial value according to the signal-to-noise ratio may be determined by the following method. By computer simulation, background white noise is superimposed on assumed input signals such as a single tone signal and a modem signal, and the distribution of the filter adaptation coefficient a2 is determined. Then, the distribution of each signal is compared, and the optimum value that allows identification is set as the initial value. Similarly, a plurality of initial values are obtained by changing the signal-to-noise ratio of each signal. As will be described later, the signal-to-noise ratio calculation circuit 3 calculates the signal power ratio of the sound part and the silent part of the input digital signal as W1.
Calculate. The initial value selection circuit 4 selects and outputs a corresponding one from among the plurality of initial values described above in accordance with the output of the signal-to-noise ratio calculation circuit 3.

Next, the outputs of the multipliers 23 and 25 are added together in an adder 27, and the result is input to a subtracter 28 as a prediction signal. The subtracter 28 subtracts the predicted signal from the input digital signal and uses its output as a residual signal. Based on the residual signal, the filter coefficient correction unit 24 and the filter coefficient correction unit 2
6 will be modified accordingly. As an example of a method for adaptively applying corrections, an adaptive predictor algorithm used in CCITT (Consultative Committee for International Telegraph and Telephone) G, 721 will be explained. Filter adaptation coefficient a, 2 filter adaptation coefficient a2. Let the residual signal d be al(k) and δ2(k)d(k) at time k, respectively, and al(+<1) and δ at time 1(-1), respectively.
2 (k 1), d (k 1), then
The filter adaptation coefficient a and the filter adaptation coefficient a2 are modified by the following equations.

at(k)・(]−δ+>at(k−1)+p+sgn
[d(k)]sgn[d(k-1)]...(1) δ3 □(1-δ2) δ2(k-1)+P2sgn[
d(k)]sgn[d(K-1)]...(2) Here, δ1. δ2 is the leakage value + T:'l, p2
is the gain.

Also, sgn is a sign function, ...(3) Defined by

Here, in the adaptive FIR filter, the unit delay circuit 21 is
-1 and the unit delay circuit 22 is Z-1, when the filter converges, it is expressed by the following equation.

1=a1Z-'-1-a2 Z-2-(4) Also, when the input signal is a single tone signal, the frequency is fO,
When the sampling period is T, Z-1 is the following formula, so Z-'=exp (-j 2πf(,T) -
(5) The filter adaptation coefficient a1 and the filter adaptation coefficient a2 when converged are expressed by the following equations.

a, = 2cos (2πfo 'r) -...
(6) δ2−−] ・・・
(7) In this way, in the case of an input signal or a single tone signal, the filter adaptation coefficient 82 does not depend on the frequency and converges to a constant value.

Furthermore, since signals other than single tone signals, such as modem signals, are modulated signals, equation (5) does not hold, and the filter adaptation coefficient a2 does not converge to -1. Therefore, by comparing the filter adaptation coefficient a2 with a threshold value, it is possible to distinguish between a modem signal and a single tone signal.

On the other hand, as for the threshold value, the optimum value differs depending on the signal-to-noise ratio between the signal power of the talking part and the signal power of the silent part such as background white noise, which is determined depending on the state of the line. The threshold value according to the signal-to-noise ratio can be determined using the following method. By computer simulation, background white noise is superimposed on assumed input signals such as a single tone signal and a modem signal, and the distribution of the filter adaptation coefficient a2 is determined. Then, the distributions of various signals are compared, and the optimum value that allows discrimination is set as a threshold value. Similarly, a plurality of threshold values are determined by changing the signal-to-noise ratio of each signal.

The signal-to-noise ratio calculation circuit 3 calculates the ratio of the signal power of the active part and the silent part of the input digital signal. The threshold selection circuit 5 selects and outputs a corresponding one of the plurality of thresholds described above in accordance with the output of the signal-to-noise ratio calculation circuit 3. - according to the filter adaptive coefficient a2 which is the output of the filter coefficient correction unit 26 and the signal-to-noise ratio input from the threshold selection circuit 5.
By comparing the variable threshold value close to 1 with the determiner 6,
It is determined whether it is a single tone, and if it is less than a threshold value, it is determined that it is a single tone and a single tone detection signal is output from the output terminal 10.

Next, the second invention will be explained.

In FIG. 2, the same components as in the embodiment of the first invention are given the same reference numerals as in FIG. That is, this embodiment is constructed by adding a low-pass filter 7, a fixed threshold input terminal 8, and a second determiner 9 to the single tone detector shown in FIG. Therefore, in this embodiment, the operation from the time when the digital signal is input to the unit delay circuit 21, the subtracter 28 and the signal-to-noise ratio calculation circuit 3 until the determiner 6 determines that it is a single tone is the same as that of the first embodiment of the first invention. They are the same, and their explanation will be omitted. In this embodiment, after the determiner 6 determines that the tone is a single tone, the low-pass filter 7 removes high frequency components of the determination result, and the second determiner 9 sets the output of the low-pass filter 7 to a fixed threshold value. By comparing, erroneous judgments due to noise superimposition etc. can be prevented and the identification rate can be improved.

For example, the first determiner 6 outputs 0.05 if it is a single tone, and otherwise determines that it is not a single tone and outputs -0.05. The output of the first determiner 6 is input to a low-pass filter 7 and integrated in the following manner. The input of the low-pass filter at time k is b + (k), and the output of the low-pass filter is b2 (
k), and the output of the low-pass filter at time -1 is defined as b2(k-1), as shown by the following equation.

b2(k)-b2(k1.)+bt(k>・
...(8) However, the output b2(k) of the low-pass filter 7
is limited by the following equation.

b2(k)≦1...(9)
The output b2(k) of the low-pass filter and a fixed threshold value (for example, 0) input from the input terminal 8 are passed to the second determiner 9.
It is determined whether it is a single tone or not by comparing with the threshold value, and if it is equal to or greater than the threshold value, it is determined that it is a single tone, and a single tone detection signal is output from the output terminal 10.

Next, FIG. 3 is a block diagram showing an example of the signal-to-noise ratio calculation circuit in FIGS. 1 and 2.

As shown in FIG. 3, the signal-to-noise ratio calculation circuit 3 includes a sound detector 31. Delay circuit 32. Signal power calculation circuit 33. It is composed of a holding circuit 34 and a comparison calculation circuit 35.

A digital signal is input to the sound detector 31 and the delay circuit 32 . The sound detector 31 identifies whether the input digital signal is sound or silent. (An example of the identification method is in the literature: ``Adaptive Threshold Speech Detector'', Institute of Electronics, Information and Communication Engineers Communication Systems Study Group CAS84-238.PP, 71-
78. (detailed in March 1985). The output of the sound detector 31 is input to a holding circuit 34 and a filter coefficient modification section 26 shown in FIGS. 1 and 2. Delay circuit 32
delays the input digital signal by a sampling time corresponding to the detection time of the sound detector 31, and its output is input to the signal power calculation circuit 33. The signal power calculation circuit 33 calculates the power of the output signal of the delay circuit 32, and the output is sent to the holding circuit 3.
4 and is input to the comparison calculation circuit 35. The holding circuit 34 holds the output of the signal power calculation circuit 33 when the input digital signal changes from a silent state to a sound state in the sound detector 31, and the output is input to the comparison calculation circuit 35. The comparison calculation circuit 35 calculates the signal-to-noise ratio of the output of the signal power calculation circuit 33 and the output of the holding circuit 34, which is the silent part power of the input signal, and sends the signal to the initial value selection circuit 4 shown in FIGS. 1 and 2. input.

〔Effect of the invention〕

As explained above, the present invention detects a single tone using an adaptive F i R filter and a determiner, and does not require a bandpass filter compared to the conventional method. The configuration circuit is always constant regardless of the number of circuits. Therefore, even if the number of sinkle tones to be detected increases, the scale of the circuit remains constant, and when implemented using a general-purpose processor, the amount of calculation of the program does not change. In addition, in the signal-to-noise ratio calculation circuit, only when the input signal changes from a silent state to a sound state, the initial value of the filter coefficient a2 is set to the signal-to-noise ratio of the signal power of the sound part and the signal power of the silent part such as background white noise. By changing the threshold value used to determine whether a single tone is present or not depending on the signal-to-noise ratio described above, it is possible to more accurately determine whether a single tone is present even when the input signal-to-noise ratio is small. can be done.

[Brief explanation of drawings]

Figures 1 and 2 are respectively 1. A block diagram of an embodiment of the single tone detector of the second invention, FIG.
2 is a block diagram showing an example of the signal-to-noise ratio calculating circuit in FIG. 2, and FIG. 4 is a block diagram showing an example of a conventional single 1H detector. 1.8...Input terminal, 2...Second-order adaptive FI R
Filter, 3... Signal-to-noise ratio calculation circuit, 1... Initial value selection circuit, 5... Threshold selection circuit, 6, 9... Judgment device, 7... Low-pass filter, ] 0 ... Output terminal, 2122 ... Unit delay circuit, 23.25 ... Multiplier, 24 ... Filter coefficient correction section, 26 ... Filter coefficient correction section, 27 ... Adder, 28. ...subtractor,
31... Sound detector, 32... Delay circuit, 33...
- Signal power calculation circuit, 34... Holding circuit, 35...
Comparison calculation circuit.

Claims (1)

[Claims] 1. A single tone detector that detects whether an input digital signal is a single tone, which detects a sound part and a silent part of an input digital signal and distinguishes between a sound part and a silent part. a signal-to-noise ratio calculation circuit that calculates the ratio of the signal power of the input digital signal; an initial value selection circuit that selects an initial value according to the output of the signal-to-noise ratio calculation circuit; A second-order adaptive FIR that predicts from a digital signal sequence and uses the output of the initial value selection circuit as the initial value of the coefficient of the filter only when the signal-to-noise ratio calculation circuit outputs a sound part from a silent part. a filter, a threshold selection circuit that selects a threshold according to the signal-to-noise ratio that is the output of the signal-to-noise ratio calculation circuit, and a variable that is the coefficient of the second-order adaptive FIR filter and the output of the threshold selection circuit. 1. A single tone detector comprising: a determiner that compares threshold values and determines whether or not the tone is a single tone. 2. In a single tone detector that detects whether an input digital signal is a single tone, detection of a sound part and a silent part of the input digital signal and the ratio of signal power between the sound part and a silent part are performed. A signal-to-noise ratio calculation circuit to calculate, an initial value selection circuit to select an initial value according to the output of this signal-to-noise ratio calculation circuit, and a prediction of an input digital signal from a previously input digital signal sequence. and a second-order adaptive FIR filter that uses the output of the initial value selection circuit as the initial value of the coefficient of the filter only when the signal-to-noise ratio calculation circuit outputs that the silent part is a sound part; A threshold selection circuit that selects a threshold according to the signal-to-noise ratio, which is the output of the noise ratio calculation circuit, and a coefficient of the second-order adaptive FIR filter, and a variable threshold, which is the output of the threshold selection circuit, are compared to select a single tone. a first determiner that determines whether or not the and a second determiner for determining whether or not the tone is a single tone by comparing the two. 3. The signal-to-noise ratio calculation circuit includes a sound detector that detects sound parts and silent parts of the input digital signal;
a delay circuit that delays an input digital signal by a sample time corresponding to the detection time of the sound detector; a signal power calculation circuit that calculates the power of the output signal of the delay circuit; a holding circuit that holds the power calculation value of the signal power calculation circuit when outputting a sound part from the signal power calculation circuit as a calculation value of the sound part signal power; 3. The single tone detector according to claim 1, further comprising a comparison calculation circuit for calculating a signal-to-noise ratio with a silent part signal power calculation value which is an output of the holding circuit.