close

Вход

Забыли?

вход по аккаунту

?

DESCRIPTION JPH11289281

код для вставкиСкачать
Patent Translate
Powered by EPO and Google
Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
financial decisions, should not be based on machine-translation output.
DESCRIPTION JPH11289281
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
howling detection method and a howling detection apparatus, and more particularly to a howling
detection method for use in an echo canceller used to realize full duplex in, for example,
handsfree telephones and video conference systems. The present invention relates to a howling
detection apparatus.
[0002]
2. Description of the Related Art In general, an echo canceler is used in hands-free telephones
and video conference systems in order to remove acoustic echo coming from a speaker to a
microphone and line echo coming from a line side. However, the impedance on the line side may
change rapidly due to the on-hook or the like of the other party's telephone, and the line echo
canceller may not follow this and howling may occur.
[0003]
Therefore, in order to avoid the occurrence of howling, a howling detection device 1 as shown in
FIG. 13 has been proposed (see FIG. 12 of JP-A-7-58674).
[0004]
The howling detection device 1 is a single tone signal detection unit configured of an echo
15-04-2019
1
canceller 2 including a phase gain shift unit 2a and a subtractor 2b, a first comparison circuit 3a,
a second comparison circuit 3b, and an AND gate 3c. And 3.
[0005]
The phase gain shift unit 2a generates a signal in which the phase and gain of the transmission
signal x (k) are shifted, and the subtractor 2b generates an echo signal y (k) transmitted from the
hybrid circuit 4 according to the phase gain shift unit 2a. The output signal is subtracted.
[0006]
Then, residual signal e1 (k) which is an output signal of subtractor 5a included in channel echo
canceler 5 and residual signal e2 (k) which is an output signal of subtractor 2b are input to first
comparison circuit 3a. And compared.
[0007]
In the first comparison circuit 3a, the absolute value circuit 3d detects the level of the residual
signal e1 (k), the low pass filter 3e removes high frequency components, and the result is input
to the comparator 3f.
Further, the level of the residual signal e2 (k) is detected by the absolute value circuit 3g, the
high frequency component is removed by the low pass filter 3h, and the signal is input to the
comparator 3f via the amplifier 3i.
[0008]
Here, if the cancellation amount by the channel echo canceller 5 is degraded due to a significant
change of the echo path and the howling occurs, the echo canceller 2 is a narrow band signal
whose howling is a single tone. The amount of cancellation that cancels howling only is increased
earlier than following changes in the echo path.
The amount of cancellation is detected by the single tone signal detector 3.
15-04-2019
2
[0009]
That is, in the first comparison circuit 3a, the level of the residual signal e1 (k) of the subtractor
5a is detected by the absolute value circuit 3d, and the level of the residual signal e2 (k) of the
subtractor 2b is the absolute value circuit 3g. When the level of the residual signal e2 (k)
becomes g dB smaller than the level of the residual signal e1 (k), the output of the comparator 3f
becomes "H".
[0010]
Further, in the second comparison circuit 3b which compares the transmission signal x (k) with
the threshold value Xth, the level of the transmission signal x (k) is detected by the absolute
value circuit 3j and the high frequency component is removed by the low pass filter 3k. After
that, it is input to the comparator 3l.
When the level of the transmission signal x (k) exceeds the threshold value Xth, the output of the
comparator 3l becomes "H".
When the outputs of the comparators 3f and 3l are both "H", the output of the AND gate 3c
which takes the logical product of these outputs becomes "H", and the howling detection signal
(HOWL) is obtained.
[0011]
As described above, in the howling detection device 1, the echo canceller 2 is added to cancel the
line echo canceller 5 earlier than the line echo canceller 5 follows the howling, and it is checked
whether the signal input from the microphone is a single tone. And howling is detected by
judging whether the level of the transmission signal x (k) is equal to or higher than the threshold
Xth.
[0012]
However, in such a howling detection apparatus 1, there has been a case where erroneous
detection may be made for howling that can not be detected as a single tone due to howling
below a certain level or distortion of a waveform. .
[0013]
15-04-2019
3
Therefore, the main object of the present invention is to provide a howling detection method and
a howling detection device capable of accurately detecting howling.
[0014]
In order to achieve the above object, the howling detection method according to claim 1
comprises the first step of counting the zero crossings of the transmission signal to the other
party, the zero crossing of the reception signal from the other party. And a third step of
determining the presence or absence of howling based on the count value of the zero crossing of
the transmission signal and the count value of the zero crossing of the reception signal.
[0015]
In the howling detection method according to claim 2, in the howling detection method according
to claim 1, in the third step, it is determined whether the count value of the zero crossing of the
transmission signal and the count value of the zero crossing of the reception signal are
substantially equal. The steps of determining and determining howling when the state in which
the count value of the zero crossing of the transmission signal and the count value of the zero
crossing of the reception signal are substantially equal continue for a predetermined time or
more.
[0016]
The howling detection method according to claim 3 includes a first step of calculating a
correlation value between a transmission signal to the other party and a reception signal from
the other party, and a second step of determining the presence or absence of howling based on
the correlation value. .
[0017]
In the howling detection method according to claim 4, in the howling detection method according
to claim 3, in the second step, a step of determining whether the correlation value is equal to or
more than a predetermined threshold, and a predetermined correlation value The method
includes the step of determining howling when the threshold value is exceeded.
[0018]
In the howling detection method according to claim 5, the first step of counting the zero crossing
of the transmission signal to the other party, the second step of counting the zero crossing of the
reception signal from the other party, the correlation value between the transmission signal and
the reception signal is calculated. And a fourth step of determining the presence or absence of
15-04-2019
4
howling based on the count value of the zero crossing of the transmission signal, the count value
of the zero crossing of the reception signal, and the correlation value.
[0019]
In the howling detection method according to claim 6, in the howling detection method according
to claim 5, the fourth step determines whether the count value of the zero crossing of the
transmission signal and the count value of the zero crossing of the reception signal are
substantially equal or not. Determining, determining whether the count value of the zero crossing
of the transmission signal and the count value of the zero crossing of the reception signal
continue for a predetermined time or longer, determining whether the correlation value is equal
to or more than a predetermined threshold And determining that the howling occurs when the
count value of the zero crossing of the transmission signal and the count value of the zero
crossing of the reception signal continue for a predetermined time or more and the correlation
value is equal to or more than a predetermined threshold. Equipped with
[0020]
The howling detection device according to claim 7 comprises a first counting means for counting
the zero crossing of the transmission signal to the other party, a second counting means for
counting the zero crossing of the reception signal from the other party, and a correlation value
between the transmission signal and the reception signal. Calculation means for calculating the
correlation value and comparing the correlation value with the threshold value, comparison
means for comparing the count value of the zero crossing of the transmission signal with the
count value of the zero crossing of the transmission signal, and comparison results and
comparison means in the correlation value calculation means And a howling determination
means for determining the presence or absence of howling based on the comparison result in
[0021]
In the howling detection method according to claim 1, instead of a single tone being detected, the
zero crossing of the transmission signal and the zero crossing of the reception signal are counted,
respectively, and howling is detected based on them.
When howling occurs, the count value of the zero crossing of the transmission signal is
compared with the count value of the zero crossing of the reception signal in view of the fact that
the count values of the respective zero crossings become approximately equal, and howling
occurs if they are approximately equal. It is determined that the
15-04-2019
5
[0022]
In the howling detection method according to claim 2, it is determined whether or not the count
value of the zero crossing of the transmission signal and the count value of the zero crossing of
the reception signal are substantially equal, and further, the state where they are substantially
equal continues for a predetermined time or more. It is determined that howling has occurred.
As described above, the accuracy of howling detection can be improved by considering the
duration of the state in which the zero-crossing count values are substantially equal.
[0023]
In the howling detection method according to claim 3, in consideration of the fact that the
correlation value between the transmission signal and the reception signal approaches 1 when a
single tone is not detected but the howling occurs, the transmission signal and the reception
signal are received. A correlation value with the signal is calculated, and howling is detected
based on the correlation value.
[0024]
In the howling detection method according to claim 4, howling is detected quickly by comparing
the correlation value with the threshold value.
[0025]
In the howling detection method according to claim 5, in the case where howling occurs, the
count values of the respective zero crosses become approximately equal, and in view of the fact
that the correlation value between the transmission signal and the reception signal approaches 1,
the transmission signal Howling is detected based on the comparison result of the count value of
the zero crossing and the count value of the zero crossing of the reception signal, and the
correlation value between the transmission signal and the reception signal.
As described above, by considering the count value and the correlation value of the zero crossing,
it is possible to improve howling detection accuracy.
15-04-2019
6
[0026]
In the howling detection method according to claim 6, the state in which the count value of the
zero crossing of the transmission signal and the count value of the zero crossing of the reception
signal are substantially equal continues for a predetermined time or more, and the correlation
value between the transmission signal and the reception signal is a threshold. If it is above, since
it is judged that howling occurred, howling detection can be performed accurately.
[0027]
In the howling detection device according to claim 7, when the howling occurs, the count values
of the zero crosses become approximately equal, and in view of the fact that the correlation value
between the transmission signal and the reception signal approaches 1, the count of the zero
crosses Since the presence or absence of howling is determined based on the comparison result
of the values and the comparison result of the correlation value and the threshold, the detection
accuracy of howling can be improved.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described below with reference to the drawings.
[0029]
Referring to FIGS. 1 and 2, echo removing apparatus 10 including a howling detector according
to an embodiment of the present invention is configured using DSP 12, ROM 14 and RAM 16.
[0030]
In the case of comparing the count value of the zero cross, the DSP 12 stores a flag
Zero_cross_flg (0: howling is not detected, 1: howling is detected) indicating the determination
result of howling based on the zero cross count value, and the correlation value is calculated. In
the case, a flag soukan_flg (0: howling not detected, 1: howling detected) indicating the
determination result of howling based on the correlation value is stored.
[0031]
The ROM 14 stores a program for controlling the operation of the echo removing apparatus 10
15-04-2019
7
and data set in advance.
As data stored in the ROM 14, when comparing the count value of the zero cross, the constant n
(for example, 1 etc.) which compensates the fluctuation of the zero cross due to the influence of
noise etc., the count of each zero cross of the reception signal and the transmission signal A
threshold THL1 for judging howling from a value is included, and when calculating a correlation
value, a constant M indicating that correlation values are obtained for M data, and a threshold
soukan_thl for howling detection are included. .
[0032]
The RAM 16 temporarily stores data such as calculated values obtained by the calculation in the
DSP 12.
As data stored in the RAM 16, when comparing the count value of the zero cross, the count value
counter1 indicating the continuation time of the state in which the count value of the zero cross
of each of the reception signal and the transmission signal is substantially equal; Buffer X_in1,
X_in_back1 of the input signal for the after-mentioned), the count value Zero_counter1 of the
number of samples between the previous zero crossing and the current zero crossing, buffer
Counter_back1 for holding the determined count value, of the input signal for the zero cross
counting unit 40 (described later) The buffer X_in2, X_in_back2, the count value Zero_counter2
of the number of samples between the previous zero crossing and the current zero crossing, and
the buffer Counter_back2 holding the determined count value are included.
In the case of calculating the correlation value, the RAM 16 also receives the variable soukan_val
in which the calculated correlation value is stored, the count values i and j used in calculating the
correlation value, and the numerator in calculating the correlation value. And a variable val2 in
which a denominator in calculating the correlation value is input, a transmission signal buffer
send_buf, and a reception signal buffer rec_buf.
The constant n, the threshold THL1, the constant M, and the threshold soukan_thl may be stored
in the RAM 16.
[0033]
15-04-2019
8
The echo canceler 10 is realized by operating the DSP 12 using programs and data stored in the
ROM 14 and the RAM 16.
FIG. 2 is a functional block diagram of the echo removing apparatus 10. As shown in FIG.
[0034]
The echo cancellation apparatus 10 shown in FIG. 2 includes an acoustic echo canceller 18, a line
echo canceller 20 and a howling detector 22.
[0035]
Near-end speaker voice and acoustic echo are input to the microphone 24, and a microphone
input signal from the microphone 24 is digitized by the A / D converter 26 and provided to the
acoustic echo canceller 18.
The acoustic echo canceller 18 receives the received signal output from the line echo canceller
20 as a reference input signal, and a pseudo echo signal is calculated using the reference input
signal.
Then, the pseudo echo signal is subtracted from the signal from the A / D converter 26, and the
removal result, that is, the transmission signal is analog converted by the D / A converter 28, and
then output as a line output signal.
The transmission signal from the acoustic echo canceller 18 is also given to the line echo
canceller 20 and the howling detector 22.
[0036]
In the line echo canceller 20, a pseudo echo signal is calculated by using the transmission signal
as a reference input signal.
15-04-2019
9
Further, a line input signal obtained by adding the line echo to the far-end speaker's voice is
input to the A / D converter 30, digitized by the A / D converter 30, and given to the line echo
canceller 20.
In the line echo canceller 20, the pseudo echo signal is subtracted from this signal, and the
removal result, that is, the received signal is analog converted by the D / A converter 32, and
then output from the speaker 34 as a speaker output signal.
The received signal from the line echo canceller 20 is supplied to the acoustic echo canceller 18
as well as to the howling detector 22 as described above.
[0037]
The howling detector 22 is configured, for example, as shown in FIG. 3 and detects howling
based on the transmission signal and the reception signal.
[0038]
The howling detector 22 includes a zero crossing comparator 36 for counting and comparing the
zero crossings of the transmission signal and the zero crossing of the reception signal, and the
zero crossing counting unit 38 of the zero crossing comparator 36 counts the zero crossings of
the transmission signal and performs zero crossing. The counting section 40 counts the zero
crossings of the received signal.
Then, the count value of the zero cross of the transmission signal and the count value of the zero
cross of the reception signal are compared by the comparison unit 42, and the howling
determination unit 44 determines the presence or absence of howling based on the comparison
result.
[0039]
The howling detection operation by the howling detector 22 of the echo removing apparatus 10
will be described with reference to FIGS. 4 to 6.
15-04-2019
10
[0040]
The overall operation of the howling detector 22 will be described with reference to FIG.
[0041]
First, the flag Zero_cross_flg stored in the DSP 12, the count value counter1 stored in the RAM
16, buffers X_in1 and X_in_back1 of input signals for the zero cross count unit 38, count values
Zero_counter1, buffers Counter_back1, and input signals for the zero cross count unit 40 The
buffers X_in2 and X_in_back2, the count value Zero_counter2, the buffer Counter_back2 and the
like are initialized (step S1).
Then, the count value of the zero cross of the reception signal is compared with the count value
of the zero cross of the transmission signal by the zero cross comparator 36 and the flag
Zero_cross_flg is set (step S3), and the howling determination unit 44 is based on the comparison
result, that is, the flag Zero_cross_flg. The presence or absence of howling is determined
according to (step S5).
[0042]
Next, the operation of step S3 will be described with reference to FIG.
[0043]
First, the zero cross count unit 38 counts zero crosses of the transmission signal (step S11), and
the zero cross count unit 40 counts zero crosses of the reception signal (step S13).
Here, the counting of the zero crossing is performed by counting the number of samples between
the previous zero crossing of the signal and the current zero crossing, and the time between the
zero crossings is calculated.
[0044]
15-04-2019
11
Then, it is determined whether (count value of zero cross of received signal) 信号 (count value of
zero cross of transmitted signal−n) (step S15), (count value of zero cross of received signal) ≧
(zero cross of transmitted signal) If it is the count value-n, it is judged whether or not (count
value of zero cross of reception signal) ((count value of zero cross of transmission signal + n)
(step S17).
If (the count value of the zero cross of the reception signal) ≦ (the count value of the zero cross
of the transmission signal + n), it is determined that the count value of the zero cross of the
reception signal and the count value of the zero cross of the transmission signal are substantially
equal. It is judged whether or not ≧ THL1 (step S19).
If counter1 ≧ THL1, the time is determined to be howling since the time for which the count
value of the zero crossing of the reception signal and the count value of the zero crossing of the
transmission signal are approximately equal continues for a predetermined time or more,
Zero_cross_flg = 1 is set (step S21), end.
If counter119THL1 in step S19, it is not possible to determine howling yet, the count value
counter1 is incremented (step S23), and the process ends.
[0045]
On the other hand, if either step S15 or step S17 is "NO", it is determined that the count value of
the zero crossing of the transmission signal and the count value of the zero crossing of the
reception signal are not substantially equal, and the flag Zero_cross_flg and the count The value
counter1 is cleared (Zero_cross_flg = 0, counter1 = 0) (step S25), and the process ends.
[0046]
Next, the operation of step S11 will be described with reference to FIG.
[0047]
First, the input signal, that is, the transmission signal is sampled by the zero cross count unit 38,
and stored in the buffer X_in1 (step S31a).
15-04-2019
12
Then, it is determined whether the code of the buffer X_in1 is equal to the code of the
transmission signal sampled immediately before it, ie, the code of the buffer X_in_back1 (step
S33a), and if both are equal, the count value Zero_counter1 is incremented (step S35a) And the
value of the buffer X_in1 is stored in the buffer X_in_back1 (step S37a).
Then, the count value held in the buffer Counter_back1 is output (step S39a), and the process
ends.
[0048]
On the other hand, if step S33a is "NO", the count value Zero_counter1 is stored in the buffer
Counter_back1, the count value of the zero crossing of the transmission signal is determined, and
the count value Zero_counter1 is cleared (Zero_counter1 = 0) (step S41a) , And proceeds to step
S37a.
[0049]
The operation of step S13 will be described with reference to FIG.
[0050]
First, the input signal, that is, the received signal is sampled by the zero cross counting unit 40
and stored in the buffer X_in2 (step S31 b).
Then, it is judged whether the code of the buffer X_in2 is equal to the code of the received signal
sampled immediately before it, that is, the code of the buffer X_in_back2 (step S33b), and if both
are equal, the count value Zero_counter2 is incremented (step S35b) And the value of the buffer
X_in2 is stored in the buffer X_in_back2 (step S37b).
Then, the count value held in the buffer Counter_back2 is output (step S39 b), and the process
ends.
[0051]
On the other hand, if the step S33b is "NO", the count value Zero_counter2 is stored in the buffer
Counter_back2, the count value of the zero crossing of the reception signal is determined, and
15-04-2019
13
the count value Zero_counter2 is cleared (Zero_counter2 = 0) (step S41b) , And proceeds to step
S37b.
[0052]
According to such howling detector 22, it is determined whether the count value of the zero
crossing of the transmission signal and the count value of the zero crossing of the reception
signal are substantially equal or not, and the howling will continue if the same state continues for
a predetermined time or more Therefore, without depending on the level of howling, it is possible
to detect howling easily and accurately even if it is low level howling or howling that can not be
detected as a single tone due to waveform distortion.
[0053]
In addition, as the howling detector included in the echo removing device 10, a howling detector
22a that detects howling based on a correlation value as shown in FIG. 8 may be used.
[0054]
The howling detector 22 a includes a correlation value calculation unit 46.
The correlation value calculation unit 46 calculates a correlation value according to Equation 1
based on the signals stored in the transmission signal buffer send_buf and the reception signal
buffer rec_buf, and the correlation value is compared with the threshold value.
Based on the comparison result, the howling determination unit 44a determines the presence or
absence of howling.
[0056]
The correlation value calculation unit 46 performs the calculation of Equation 1 from j = 0 to j =
M-1, and sets the maximum value as the correlation value.
The correlation value takes a value in the range of 0 to 1.0, and when the correlation value is
15-04-2019
14
greater than or equal to a preset threshold soukan_thl, it is determined that the howling state is
established.
As described above, in Equation 1, send_buf represents a transmission signal buffer, and rec_buf
represents a reception signal buffer.
[0057]
The howling detection operation by such howling detector 22a will be described with reference
to FIGS. 9 and 10. FIG.
[0058]
The overall operation of the howling detector 22a will be described with reference to FIG.
[0059]
First, the flag soukan_flg stored in the DSP 12, the variables soukan_val, val1 and val2, count
values i and j, the transmission signal buffer send_buf, the reception signal buffer rec_buf and
the like stored in the RAM 16 are initialized (step S51).
Then, the correlation value detection unit 46 calculates a correlation value using Expression 1
and the correlation value is compared with a threshold to set a flag soukan_flg (step S53).
Based on the comparison result, that is, the flag soukan_flg, the howling determination unit 44a
determines the presence or absence of howling (step S55), and the process returns to step S53.
[0060]
Next, the operation of step S53 will be described with reference to FIG.
[0061]
First, variables soukan_val and count value j are initialized (soukan_val = 0, j = 0) (step S61), and
15-04-2019
15
count value i, variables val1 and val2 are initialized (i = 0, val1 = 0, val2 = 0) (Step S63).
Then, the transmission signal and the reception signal are stored in the transmission signal
buffer send_buf and the reception signal buffer rec_buf, respectively, and the value of the
numerator of the equation 1 or the variable val1 and is based on the value of the base
transmission signal buffer send_buf and the value of the reception signal buffer rec_buf. The
value of the denominator, that is, the variable val2 is integrated (step S65).
i is incremented (step S67), and it is determined whether i ≦ M−1 or not (step S69).
Steps S65 and S67 are repeated until i = M-1. If i = M-1, then the numerator and denominator of
Equation 1 become the values obtained by integrating M variables val1 and val2, respectively.
[0062]
Then, if "NO" in step S69, i.e., i> M-1, it is determined whether (val1 / val2)> soukan_val or not
(step S71). If (val1 / val2)> soukan_val, the variable soukan_val is It is updated to (val1 / val2)
(step S73), and the process proceeds to step S75. If (val1 / val2)> soukan_val does not hold in
step S71, the variable soukan_val is not updated, and the process proceeds to step S75. In this
way, the variable soukan_val is updated to a large value.
[0063]
Then, the variable j is incremented (step S75), and it is determined whether j ≦ M−1 or not
(step S77). As long as j ≦ M−1, steps S63 to S75 are repeated, correlation values are obtained
for the M data, and the maximum correlation value, that is, variable soukan_val is obtained.
[0064]
If "NO" in the step S77, it is judged whether or not soukan_val sou soukan_thl (step S79). If
soukan_val sou soukan_thl, soukan_flg = 1 is set (step S81) and the process is ended. If
soukan_val sou soukan_thl in step S79, soukan_flg = 0 is set (step S83), and the process ends.
15-04-2019
16
[0065]
According to such a howling detector 22a, the correlation value between the transmission signal
and the reception signal becomes a predetermined threshold soukan_thl in view of the fact that
the correlation value between the transmission signal and the reception signal approaches 1
when howling occurs. Because the comparison is performed and the howling is detected based
on the comparison result, the howling is quickly performed even if it is not detected as a single
tone due to low level howling or waveform distortion without depending on the level of howling.
As a result, the howling sound can be eliminated early.
[0066]
Furthermore, as the howling detector included in the echo removing device 10, a howling
detector 22b that detects howling based on the comparison result of the count value of the zero
cross and the detection result based on the correlation value as shown in FIG. It is also good.
[0067]
The zero cross comparator 36 and the correlation calculation unit 46 included in the howling
detector 22 b are the same as the zero cross detector 36 shown in FIG. 3 and the correlation
calculator 46 shown in FIG.
The howling determination unit 44b determines the presence or absence of howling based on the
comparison result of the zero cross comparison unit 36 and the comparison result of the
correlation value calculation unit 46.
[0068]
The howling detection operation by such a howling detector 22b will be described with reference
to FIG.
[0069]
The overall operation of the howling detector 22b will be described with reference to FIG.
[0070]
15-04-2019
17
First, flags Zero_cross_flg, soukan_flg stored in the DSP 12, the count value counter1 stored in
the RAM 16, buffers X_in1 and X_in_back1 of the input signal for the zero cross count unit 38,
count value Zero_counter1, input for the buffer Counter_back1 and the zero cross count unit 40
The buffer X_in2 and X_in_back2 of the signal, the count value Zero_counter2, the buffer
Counter_back2, the variables soukan_val, val1 and val2, the count values i and j, the transmission
signal buffer send_buf, the reception signal buffer rec_buf and the like are initialized (step S91).
[0071]
Then, the count value of the zero cross of the reception signal is compared with the count value
of the zero cross of the transmission signal by the zero cross comparator 36, the flag
Zero_cross_flg is set (step S93), and the correlation value calculation unit 46 A value is
calculated, the correlation value is compared with the threshold value, and the flag soukan_flg is
set (step S95).
The howling determination unit 44b determines the presence / absence of howling based on the
comparison results of the count value of the zero cross and the comparison result of the
correlation value and the threshold, that is, the flag Zero_cross_flg and the flag soukan_flg (step
S97), and returns to step S93.
[0072]
The details of the operation of step S93 are shown in FIG. 5, FIG. 6, and FIG. 7, and the details of
the operation of step S95 are shown in FIG.
[0073]
According to such a howling detector 22b, the count value of the zero crossing of the
transmission signal and the count value of the zero crossing of the reception signal are
substantially equal and the state continues for a predetermined time or more, and the correlation
value between the transmission signal and the reception signal Since it is determined as howling
if the value of L is a predetermined value or more, low level howling and howling that can not be
detected as a single tone due to distortion of the waveform can be made even more accurately
without depending on the level of howling. Howling can be detected.
[0074]
The present invention can be applied to, for example, a fax modem with a voice recording and
15-04-2019
18
reproducing function.
[0075]
It goes without saying that a CPU may be used instead of the DSP 12.
[0076]
According to the present invention, howling can be accurately detected even for howling that can
not be detected as a single tone due to low level howling or waveform distortion.
15-04-2019
19
Документ
Категория
Без категории
Просмотров
0
Размер файла
28 Кб
Теги
description, jph11289281
1/--страниц
Пожаловаться на содержимое документа