JPH0360559A - Echo suppressing device for loudspeaker telephone set - Google Patents

Abstract

PURPOSE:To ensure the echo suppression effect without deteriorating the voice quality by synthesizing a component composed of mainly a direct wave with a fixed filter and using a subtraction means to eliminate an echo while keeping it as an analog signal through a simulated echo converted into an analog signal at a D/A converter. CONSTITUTION:A component composed mainly of a direct wave in an echo detoured from a loudspeaker 1 to a microphone 2 is synthesized with a fixed filter 8 and eliminated by a subtraction means 7 while being kept to an analog signal with a simulating echo converted into an analog signal at a 1st D/A converter 9 and a signal with a direct wave component having a high signal level eliminated therefrom is inputted to a 2nd D/A converter. Since the fixed filter 8 mainly synthesizes the direct wave, the scale of the filter is enough to be comparatively small and has the equivalent delay time of nearly 5msec. Thus, voice with excellent quality is sent to ensure the echo suppressing effect.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an echo pressing device for a loudspeaker telephone that suppresses howling and echoes in the loudspeaker telephone.

BACKGROUND OF THE INVENTION In recent years, attempts have been made to apply echo cancellers, which have been put into practical use in electronic conference systems, to loudspeaker telephones to realize a loudspeaker telephone that can carry out simultaneous calls.

The conventional echo suppression device for a loudspeaker telephone will be described below with reference to the drawings.

FIG. 4 shows the configuration of a conventional echo suppression device for a public address telephone. In FIG. 2, 1 is a loudspeaker, 2 is a microphone, 3 is a first analog-to-digital converter that converts the received input signal from analog to digital, and 4 is a second converter that converts the output of microphone 2 from analog to digital. 5 is an analog-to-digital converter; 5 is an adaptive echo canceller that removes echo from the output of the second analog-to-digital converter 4 while sequentially estimating the characteristics of the echo path using the speech voice; 6 is an adaptive echo canceller of the adaptive echo canceller 5; This is a digital-to-analog converter that converts the output from digital to analog.

The operation of the echo suppression device for a loudspeaker telephone configured as described above will be described below.

The reception input signal is converted into a digital signal by the first analog-to-digital converter 3, inputted to the adaptive echo canceller 5, and converted into an acoustic signal by the loudspeaker 1. The sound amplified by the loudspeaker 1 not only reaches the speaker but is also collected by the microphone 2. The sound picked up by the microphone 2 is converted into a digital signal by the second analog-to-digital converter 4 and input to the adaptive echo canceller 5. The adaptive echo canceller 5 estimates the characteristics of the echo path from the loudspeaker 1 to the microphone 2, performs convolution with the output signal of the analog-to-digital converter 3 to synthesize a pseudo echo, and generates a signal from the output of the second analog-to-digital converter 4. Eliminate echo by subtraction.

Problems to be Solved by the Invention However, in the above configuration, when a loudspeaker and a microphone are installed in close proximity to each other in one housing like a loudspeaker telephone, the sound level of the loudspeaker is higher than the speaker's voice level picked up by the microphone. The echo signal that comes around from the source becomes larger. For example, if the distance between the microphone and the speaker is 60 cm, and the distance between the loudspeaker and the microphone is 15 cm+, then the echo coming from the loudspeaker to the microphone will have a level four times higher than the speaker's voice level. Therefore, if the input of the second analog-to-digital converter that converts the microphone output signal into a digital signal is not saturated, the quantization accuracy for the speaker's voice to be transmitted will deteriorate, resulting in deterioration of the voice quality and This results in a drawback that the amount of echo cancellation of the echo canceller decreases, and the echo suppression effect decreases.

In view of the above-mentioned problems, the present invention has been developed to transmit sound without deteriorating the quality and ensure the echo suppression effect even when a loudspeaker and a microphone are installed in close proximity to each other in one housing as in the case of such a loudspeaker telephone. The present invention provides an echo suppression device for a public address telephone.

Means for Solving the Problems In order to achieve the above objects, the echo suppression device for a public address telephone according to the present invention comprises a loudspeaker for amplifying the received voice, a microphone for collecting the voice of the speaker, and an analog received input signal. A first analog-to-digital converter converts the echo into a digital signal, and the echo, which is mainly the direct sound coming from the loudspeaker to the microphone, is converted into a digital signal by using the pre-determined echo path characteristics and the first analog-to-digital converter. a fixed filter that synthesizes by convolution operation with the received input signal; a first digital-to-analog converter that converts the output of the fixed filter from a digital signal to an analog signal; a subtracter that subtracts the output; a second analog-to-digital converter that converts the analog signal output from the subtracter into a digital signal; and a second analog-to-digital converter that sequentially estimates the characteristics of the echo path using the voice of the call. The adaptive echo canceller further removes echo from the output of the echo canceller, and the second digital-to-analog converter converts the output signal of the adaptive echo canceler from a digital signal to an analog signal.

Effect: With this configuration, among the echoes that come from the loudspeaker to the microphone, components that are mainly direct waves are synthesized by the fixed filter, and the pseudo echoes that are converted into analog signals by the first digital-to-analog converter generate Since the analog signal is removed as it is by the subtraction means, and the direct wave component with a high signal level is removed, it is input to the second analog-to-digital converter, so the quantization accuracy of the speaker's audio signal may deteriorate. Therefore, the echo cancellation amount of the adaptive echo canceller is reduced, and the echo suppression effect is not degraded, thereby making it possible to provide an echo suppression device for a public address telephone that can transmit high-quality voice and ensure the echo suppression effect.

EXAMPLE An example of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an echo suppression device for a public address telephone according to an embodiment of the present invention. In FIG. 1, 1 is a loudspeaker, 2 is a microphone, 3 is a first analog-to-digital converter that converts a received input signal from analog to digital, and 4 is a second analog converter that converts a transmitted input signal from analog to digital. 5 is an adaptive echo canceler that removes echo from the output of the second analog-to-digital converter 4 while sequentially estimating the characteristics of the echo path using the speech voice; 6 is the output of the adaptive echo canceller 5; This is a second digital-to-analog converter that converts from digital to analog. The above is the same as the conventional example. Reference numeral 8 denotes a fixed filter that synthesizes a component consisting mainly of direct waves of the echo signal that goes around from the loudspeaker 1 to the microphone 2, and 7 a subtractor that subtracts the echo signal synthesized by the fixed filter 8 from the output of the microphone 2. 9 is a first digital-to-analog converter that converts the digital output of the fixed filter 8 into an analog signal.

The operation of the echo suppression device for a loudspeaker telephone configured as described above will be explained below.

Among the echoes coming from the loudspeaker 1 to the microphone 2, components mainly consisting of direct waves are synthesized by a fixed filter 8, and then sent to a first digital-to-analog converter 9.
The pseudo echo converted into an analog signal is removed as an analog signal by the subtracting means 7, and is inputted to the second analog-to-digital converter 4 with the direct wave component having a high signal level removed. Since the fixed filter 8 mainly synthesizes direct waves, the scale of the filter may be relatively small and has an equivalent delay time of about 5 m5ec.

On the other hand, the adaptive echo canceller 5 has a larger equivalent delay time (2011 sec to several 100 m5 ec) than the fixed filter 8 in order to cancel multiple reflections from indoor walls, speakers, etc.

As described above, according to this embodiment, among the echoes that come from the loudspeaker to the microphone, components mainly consisting of direct waves are synthesized by the fixed filter, and converted into analog signals by the first digital-to-analog converter. The resulting pseudo echo is removed as an analog signal by a subtraction means,
Since the direct wave component with a high signal level is input to the second analog-to-digital converter after being removed, the quantization accuracy of the speaker's voice signal deteriorates, and the amount of echo cancellation of the adaptive echo canceller decreases. However, the echo suppression effect does not deteriorate, and it is possible to provide an echo suppression device for a public address telephone that can transmit high-quality voice and ensure the echo suppression effect.

Effects of the Invention Since the present invention is configured as described above, it exhibits the effects described below.

Among the echoes transmitted from the loudspeaker to the microphone, components mainly consisting of direct waves are synthesized by a fixed filter, and a pseudo echo is converted into an analog signal by a first digital-to-analog converter. Since the direct wave component with a high signal level is input to the second analog-to-digital converter after being removed, the quantization accuracy of the speaker's voice signal may deteriorate, and the echo of the adaptive echo canceller may deteriorate. It is possible to provide an echo suppression device for a loudspeaker telephone that can transmit high-quality sound and ensure the echo suppression effect without reducing the amount of cancellation and reducing the echo suppression effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an echo canceling device for a public address telephone according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a conventional echo canceling device for a public address telephone. DESCRIPTION OF SYMBOLS 1... Loudspeaker, 2... Microphone, 3... First analog-to-digital converter, 4... Second analog-to-digital converter, 5
...Adaptive echo canceller, 6...
2nd digital-to-analog converter, 7... subtracter, 8... fixed filter, 9... first
digital to analog converter.

Claims (1)

[Claims] a loudspeaker that amplifies the received voice, a microphone that collects the speaker's voice, a first analog-to-digital converter that converts the analog received voice input signal into a digital signal, and a signal that is transmitted from the loudspeaker to the microphone. a fixed filter that synthesizes an echo mainly composed of direct sound by convolution operation between a predetermined characteristic of an echo path and a reception input signal digitized by the first analog-to-digital converter; and an output of the fixed filter. a first digital-to-analog converter for converting a digital signal into an analog signal; a subtracter for subtracting the output of the first analog-to-digital converter from the output of the microphone; and converting the analog signal output from the subtracter into a digital signal. a second analog-to-digital converter for converting the second analog-to-digital converter into a second analog-to-digital converter; and a second digital-to-analog converter that converts the output signal of the type echo canceler from a digital signal to an analog signal.