JP2919422B2 - Echo canceller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo canceller, and more particularly, to an echo canceller used for a hands-free automobile telephone for a vehicle.

[0002]

2. Description of the Related Art Conventionally, in a hands-free telephone mounted on a vehicle, a part of the received voice goes around a microphone to generate an echo in order to listen to the received voice through a speaker. This degrades the call quality and causes howling in severe cases. In order to prevent this inconvenience, the estimated value of the impulse response of the echo path is internally stored, the received signal is input, the echo is estimated by convolution with the received signal, and the estimated echo is added to the transmitted signal to be transmitted. There is an echo canceller that cancels the echo.

[0003] However, when mounted on a vehicle, it is always exposed to ambient noise, unlike when used indoors. This ambient noise hinders the estimation of the echo of the received signal in the episode signal and degrades the accuracy. As a result, the amount of echo cancellation decreases and the call quality deteriorates. Japanese Patent Application 63
Japanese Patent No. 43451 discloses an attempt to improve this point. According to this publication, a noise canceling circuit is added as a measure against noise.

FIG. 2 is a block diagram showing the configuration of this conventional example. In FIG. 2, 101 is a hand-free microphone,
102 is a hand-free speaker, 103 is a finite impulse response type (FIR) or an infinite impulse response type (IIR).
Digital signal processing means (noise canceller) for noise cancellation, comprising
4 is connected to the noise canceller 103 in succession,
This is a digital signal processing means (echo canceller) for echo cancellation which is constituted by an equivalent filter.

[0005] Further, reference numeral 105 denotes a transmission / reception determination circuit,
Reference numeral 07 denotes an insertion loss that is inserted into the electric circuit of the hand-free microphone 101 or the hand-free speaker 102 and is controlled by the transmission / reception determination circuit 105. In this example, variable gain amplifiers are used. An audio level detector 110 detects the audio level of a channel or a transmission path and sends it to the transmission / reception determination circuit 105. Reference numeral 110 denotes a voice including these transmission / reception determination circuit 105, insertion losses 106 and 107, and audio level detectors 108 and 109. Switch.

[0006] The basic operation is noise cancellation 103.
Ambient noise and reverberation are removed by the echo canceller 104, and transmission / reception is determined by the voice switch 110, and the insertion loss 106 or 1 is determined on the predetermined side.
07 is inserted to switch between transmission and reception. The voice switch 110 realizes two-way simultaneous communication and has no operational relationship with the direct echo canceller.

[0007]

As described above, in the conventional example, the ambient noise which reduces the effect of the echo canceller is suppressed by the noise canceller arranged before the echo canceller. The circuit configuration of this noise canceller is And the use of two sets of such a circuit configuration has a problem that the entire circuit becomes complicated.

[0008]

An echo canceller according to the present invention has an estimated value of an impulse response of an echo path therein, inputs a received signal, estimates the echo by convolution operation with the received signal, and estimates the echo. And a band elimination filter for extracting noise other than the transmission voice band from the transmission signal, and an output signal of the band elimination filter is added to the reception signal. And an adder.

Further, the band elimination filter may be a low-pass filter for extracting noise in a transmission voice band.

[0010]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. This figure shows the overall configuration of a hands-free mobile phone using the echo canceller 1 of the present invention.
An echo canceller 1 for canceling an echo, a microphone 5 for generating a transmission signal on the transmission side, a speaker 6 for converting a reception signal into voice, a voice switch 2 for realizing two-way simultaneous communication, and a transmission signal using radio waves. It comprises a transmitter 3 for transmitting and a receiver 4 for converting a received radio wave into a received signal.

The configuration of the echo canceller 1 is such that the transmission signal 1
01, a band elimination filter (BEF) 11 for blocking the transmission signal in the voice band 01 and extracting ambient noise in the upper and lower bands, an echo canceller body 12 for canceling the echo, an estimated echo output from the echo canceller, and a transmission signal An adder 13 adds the received signal 101 and the output signal of the BEF 11.

Next, the operation of the echo canceller 1 will be described. The echo canceller main body 12 internally has an estimated value of an impulse response of a reverberation path in which the received voice of the speaker 6 goes around the microphone 5, receives the received signal 101, estimates the echo by convolution with the received signal, and estimates the echo. This is an echo canceller using an adaptive filter that adds an estimated echo to a transmission signal 101 to be transmitted and cancels the echo.

A transmission signal 101 obtained by combining the transmission signal, the ambient noise, and the echo from the microphone 5 enters the BEF 11, and
Ambient noise distributed in the upper and lower bands of the voice band (about 300 Hz to 3 KHz) is extracted. The level of the ambient noise is largely dominant on the low frequency side. The ambient noise extracted by the BEF 11 is added to the received signal 102 by the adder 14 and input to the echo canceller main body 12. The echo canceller main unit 12 internally performs an arithmetic process based on the output of the adder, that is, the received signal in consideration of the ambient noise, and outputs an optimum estimated echo in this state. Transmission signal 1
01 is added to the estimated echo by the adder 13, and the echo component is sufficiently eliminated without being affected by noise, and the ambient noise is also eliminated at the same time.

The BEF 11 may use a low-pass filter (LPF) whose circuit is simple because ambient noise is mainly distributed on the low frequency side.

[0016]

As described above, the echo canceller of the present invention extracts the ambient noise contained in the transmission signal, adds it to the received signal, and performs the arithmetic processing. Therefore, the amount of echo suppression due to the influence of the ambient noise is reduced. Since the noise is not reduced and the noise is reduced, there is an effect that communication quality can be ensured.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a conventional example.

[Description of Signs] 1 echo canceller 2 voice switch 3 transmitter 4 receiver 5 microphone 6 speaker 11 band elimination filter (BEF) 12 echo canceller main body 13, 14 adder

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-221821 (JP, A) JP-A-8-8789 (JP, A) JP-A-8-65211 (JP, A) JP-A-1- 198155 (JP, A) JP-A-63-43451 (JP, A) JP-A-4-344722 (JP, A) JP-A-2-262726 (JP, A) JP-A-63-263865 (JP, A) JP-A-63-191447 (JP, A) JP-A-58-63207 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04M 1/60 H04B 3/23 H04M 9/08 H04R 3/02

Claims (2)

(57) [Claims] An echo is estimated by performing a convolution operation with a received signal having an estimated value of an impulse response of a reverberation path therein, and adding the estimated echo to a transmission signal to be transmitted to eliminate the echo. An echo canceller, comprising: a band elimination filter for extracting noise other than a transmission voice band from the transmission signal; and an adder for adding an output signal of the band elimination filter to the reception signal. Canceller. 2. The echo canceller according to claim 1, wherein said band elimination filter is a low-pass filter for extracting noise in a band lower than a transmission voice band.