Communications – electrical: acoustic wave systems and devices – Distance or direction finding – With time interval measuring means
Reexamination Certificate
2001-02-15
2003-02-25
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
With time interval measuring means
C367S125000
Reexamination Certificate
active
06525993
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a speaker direction detection circuit and to a speaker direction detection method used in the circuit, and more particularly to the detection circuit and method of a device that detects the direction of a speaker as seen from the device by means of speech signals and that is used in controlling the video camera imaging angle of a device that incorporates an video camera for image input and a microphone for speech input used in a television conference device.
2. Description of the Related Art
As described in “7.2 Techniques for estimating the direction of arrival and power of sound” from “Sound Systems and Digital Processing” (Oga, Yamazaki, Kaneda, Institute of Electronics, Information and Communication Engineers Conference, Mar. 25, 1995, p. 197), the cross-correlation function is typically used as a means for detecting the difference in arrival times (delay) at the two microphones in devices for detecting the direction of a speaker.
This cross-correlation function is calculated, and as shown in
FIG. 1
or
FIG. 2
, the difference in arrival times (delay) can be detected from the maximum value of the cross-correlation function. It is generally known that the direction of arrival of sound waves can be estimated from this time difference (delay). In other words, the direction of arrival of sound waves and the time difference between signals received at each of a plurality of microphones are in a one-to-one relation, and if these time differences can be estimated, the direction of arrival of the sound waves can also be estimated.
FIG.
1
and
FIG. 2
are explanatory views of a typical detection method for detecting both the horizontal direction position and vertical direction position of arriving sound waves. Angle &thgr; in the horizontal direction of sound waves that arrive at microphones M
1
and M
2
in
FIG. 1
is detected by the equation:
L sin &thgr;=&ggr;Th
&thgr;=sin
−1
(&ggr;Th/L)
In this case, the time difference (delay) Th can be found from: sampling period (seconds)×difference (number of samples). The vertical angles of sound waves that arrive at microphones M
2
and M
3
in
FIG. 2
can also be estimated from similar equations.
As shown in
FIG. 3
, sound waves that arrive from direction &thgr;
s
are assumed to be plane waves, and it is assumed that these plane waves are received at two microphones M
1
and M
2
that are installed separated by a distance d from each other. At this time, the received signals &khgr;
1
(t) and &khgr;
2
(t) of each of microphones M
1
and M
2
are in the relation:
&khgr;
2
(
t
)=&khgr;
1
(
t−&tgr;
s
)
&tgr;
s
=(
d
×sin (&thgr;
s
)/
c
)
where c is the speed of sound.
Conversely, if the time difference (s between signals ((t) and (2(t) is known, the arrival direction (s of the sound waves can be found from the following equation:
&thgr;
s
=sin
−1
(
c·&tgr;
s
/d
)
Based on the cross-correlation function &phgr;
12
(&tgr;) of &khgr;
1
(t) and &khgr;
2
(t), time difference (&tgr;
s
is:
φ
12
(
τ
)
=
E
[
χ
1
(
t
)
·
χ
2
(
t
+
τ
)
]
=
E
[
χ
1
(
t
)
·
χ
1
(
t
+
τ
-
τ
s
)
]
=
φ
11
(
τ
-
τ
s
)
where E[·] represents the expected value, and &phgr;
11
(&tgr;) represents the autocorrelation of &khgr;
1
(t).
Since it is known that autocorrelation function &phgr;
11
(&tgr;) reaches a maximum at &tgr;=0, &phgr;
12
(&tgr;) attains a maximum at &tgr;=&tgr;
s
. From this, &tgr;
s
is obtained if cross-correlation function &phgr;
12
(&tgr;) is calculated and &tgr; that gives the maximum value is found, and the direction of the sound waves can be estimated if this value is substituted into the equation for finding the arrival direction &thgr;
s
. Accordingly, the arrival delay time is found based on this estimation result, and the operation of converting to and outputting the speaker's direction is then carried out.
It is already known that cross-correlation function &phgr;
12
(&tgr;) will have a relatively sharp peak if the frequency bandwidth is broad. Thus, &tgr;
s
can be accurately estimated despite the addition of noise if the peak is sharp. However, because the sharpness of the peak is influenced by the frequency bandwidth of the sound wave signal and because there is also influence from noise, some method must be used to eliminate the influence of error.
In the method disclosed in Japanese Patent Laid-open No. 123311/1995, for the purpose of controlling the image pickup angle of the camera of an image pickup device, a unidirectional microphone and a bidirectional microphone are used as the audio signal input sources and as a means for receiving the voice signal of the subject and detecting direction; and a means is used for synchronizing the output signals of these two microphones, calculating the phase difference by way of a sensitivity adjustment means of the microphones, and detecting the direction of the subject.
In the speaker direction detection method of the prior art that is described above, there is the problem that, in a case in which the output signals of the speaker direction detection device are used to control the shooting angle of the video camera, the occurrence of errors in detection of the speaker's direction cause the video camera to be directed in a direction other than the speaker, causing great inconvenience for the users of the television conference device. Erroneous operation is particularly frequent because the results of the cross-correlation function are used without modification, and direction detection control cannot be realized without adopting some countermeasure.
In the prior art disclosed in Japanese Patent Laid-open No. 123311/1995, moreover, it is believed that erroneous detection may occur due to the influence of variations in the characteristics of the microphones when phase difference is calculated through the sensitivity adjustment means of the microphones.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a speaker direction detection circuit and a speaker direction detection method that is used in the circuit that solve the above-described problems, that can reduce erroneous detection of the speaker's direction even when signals that arrive from directions other than that of the speaker combine with the speaker's speech signals, and that can increase stability.
The speaker direction detection circuit according to the present invention is provided with: an evaluation function means that uses added values of a cross-correlation function for each time difference to estimate arrival time differences that arise from differences in the distance for speech signals to reach two microphones; and a detection means that detects the maximum value of said added values of the cross-correlation function to detect the direction of a speaker.
Another speaker direction detection circuit according to the present invention is provided with: an evaluation function means that uses an evaluation function according to a relational formula between an autocorrelation function and a cross-correlation function to estimate arrival time differences that arise from differences in the distance for speech signals to reach two microphones; and a detection means that detects the maximum value of said evaluation function to detect the direction of a speaker.
The speaker direction detection method according to the present invention includes steps of: using added values for every time difference of a cross-correlation function to estimate arrival time differences that arise from differences in distance for speech signals to reach two microphones; and detecting the maximum value of said added values of the cross-correlation function to detect the direction of a speaker.
Another speaker direction detection method according to the present invention includes steps of: using an
Sasada Taisuke
Wake Yasuhiro
NEC Corporation
Pihulic Daniel T.
Sughrue & Mion, PLLC
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