JPS6130161A - Audio conference device - Google Patents

Abstract

PURPOSE:To perform the audio conference service with a good S/N by inputting the electric converted output of a microphone for spoken voice input and that of a microphone for background sound input to a subtractor after they are adjusted with the gain of a balance amplifier and cancelling background sounds. CONSTITUTION:A comparator 10 compares a power level corresponding to the microphone input sound in the input terminal of a variable loss device 4 of a transmitting system with that corresponding to the heard voice to be outputted from a speaker in the output terminal of a variable loss device 7 of a receiving system. Loss devices 4 and 7 are controlled in accordance with the discrimination output of the comparator 10 by a gain control part 11, and the loss of the loss device 4 is reduced and that of the loss device 7 is increased in the speaking mode, and gains are controlled in accordance with the speaking mode and the hearing mode. A microphone 2 for background sound input is provided besides a microphone 1 for speaking subscriber' voice input, and the difference between two microphone inputs whose balance is adjusted through gains 1a and 2a with respect to phase and gain is operated by a subtractor 12, and thereby, background sounds are erased and voice components of the speaking subscriber from the microphone 1 remain.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a so-called audio teleconference system, and in particular transmits speeches from each conference room connected by a transmitting/receiving network to other conference rooms, and uses speakers. There is a speaking mode that outputs (notifies) through the conference room, and a listening mode that receives microphone input from other conference rooms and outputs it through the speaker to listen to what others are saying.Basically, the transmission path and reception path are Concerning conference audio control in audio teleconference systems coupled and managed in dual communication mode.

<Prior art> In such a system, conference rooms are basically connected in dual communication mode, so that audio transmitted from one conference room in speech mode using a microphone is output from a speaker in another conference room; The sound entered into the microphone in the conference room forms a loop, so if the loop gain of this loop increases to a certain extent, it will cause so-called howling oscillation, so the loop gain including the reverberation and attenuation of the conference room must be kept below 1. Therefore, in such a system, in order to control the loop gain formed with other conference rooms to 1 or less, gain switching control is performed such that increasing the gain on the transmitting side decreases the gain on the receiving side. Control is performed to increase the transmitter side, and the input level of audio information entering the microphone in the conference room is monitored as "key" information for automatic switching between speaking mode and listening mode. Automatic mode switching is also known in which when the input level exceeds a certain preset threshold value, this is used as a "key" to switch to the speech mode.

[Problem] However, with this kind of control, if the sound heard from the speaker cannot be said to be the same as the speech in the own conference room, or if the so-called noise level such as the generated sound is above a certain level, the system will not return from the speaking mode due to the level. However, in order to prevent this, the microphone input threshold has to be set high (and there was a problem in that the microphone input voice level of the speaker would require a loud voice to switch to the speaking mode.

<Solution Means> The present invention solves the above problems. <Compared to the conventional configuration, a first microphone device that inputs the speaker's voice by devising a microphone input end (uses a microphone with good directivity) There are two input systems: a second microphone device (using an omnidirectional or nearly omnidirectional microphone) that inputs the background sound of the conference room outside the conference room, and the inputs from these two input systems are processed by their respective amplifiers to adjust the mutual gain and phase. After adjusting, the background bone is subtracted by a subtractor, and the output from this subtractor is used as the output for the transmitting system, and the output level for the receiving system and the output level for the transmitting system are compared using a comparator as in the conventional method. By using the level ratio (the difference is the same) between the two as a "key" and setting the transmitting system gain and receiving system gain corresponding to the mode and the mode by controlling the respective variable loss devices. It is something to be solved.

<Function> According to this configuration, if the output from the microphone for the transmitting system is viewed with a comparator, the background level has been subtracted, so the output from the microphone for the transmitting system is subtracted from the background sound, so it is the speech input from the first microphone device with the background sound subtracted. The level of only the signal voice of the user is used as one of the comparison targets, and it is possible to reliably switch between the speaking mode and the listening mode just by comparing the levels without being affected by background sounds.

<Embodiment> FIG. 1 is an explanatory diagram of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of a conventional configuration for comparison, both of which show the configuration of one conference room connected to the system.

The system referred to here is established by connecting several of these configurations via transmission lines.

As is almost clear from the diagram, speaking microphone 1. ．． The audio input from 1' is electrically converted, amplified by an amplifier 3, passed through a variable loss device 4 in a transmission system, and sent out to a transmission line via a transmitter 5. (Of course, there is another conference room connected to the other side of the transmission path, and the receiver on that side receives and outputs the signal, and the transmitted speech output from that side is also returned.) One-way transmission There is a receiver 6 at the receiving end of the channel, which receives the incoming signal, and the gain is adjusted via a receiving variable loss device 7, and the sound is outputted from a speaker 9 via a power amplifier 8.

On the other hand, the comparator 10 compares the power level corresponding to the microphone input audio at the input end of the transmitting system variable loss device 4 (output end of the amplifier 3) with the output end of the receiving system variable loss device 7, (input end of the power amplifier 8). ), and according to the judgment output of the comparator 10, the mode gain control section 11 controls both variable loss devices 4 and 7 to correspond to the speaking and listening modes. In the speaking mode, the loss of the transmitting variable loss device 4 is small, and the loss of the receiving variable loss device 7 is small.
The gain is controlled according to the mode by increasing the loss. The configuration of this embodiment has a microphone 2 for background sound input in addition to the microphone 1 for inputting speaker's voice, and the balance is adjusted for phase and gain via amplifiers la and 2a that can be adjusted for gain balance. When the difference between the two microphone inputs is taken by the subtractor 12, the background sound is erased with the same gain level and the phase of 180°, and the vocalization component of the speaker from the microphone 1 remains.

Note that this cancellation by subtraction cannot be carried out in a practical manner unless the frequency gain characteristics 9 phase characteristics and distortion of the microphone, amplifier 2, etc. are the same, and the input background sound is not the same. From a perspective, 500-3
Since it is sufficient that the level is practically reduced around 000Hz, select the same type of microphone and amplifier,
It has been confirmed on a practical level that the background sound level can be reduced by adjusting the gain balance to find the minimum value and also adjusting the phase if necessary.

By adding these background sound input microphones, balance amplifiers, and subtractors, the level of the speaker's voice from microphone 1 will be lowered by the level of the background, so it will be possible to transmit the background sound to the other party. Since it is less susceptible to influence, mode switching based on power comparison becomes more reliable.

<Effects> As explained above, according to the present invention, signals can be transmitted with a good signal-to-noise ratio even when the background sound is large, and mode switching can be reliably performed just by power comparison. It has the characteristic effect of helping to improve one's abilities.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention, and FIG. 2 is an explanatory diagram of a corresponding conventional example. In the figure, 1.1' is a microphone for inputting speech, 2 is a microphone for background sound input, La and 2a are amplifiers for gain balance, 1
2 indicates a differentiator. Further, 3 is an amplifier, 4 is a transmitting system variable loss device, 7 is a receiving system variable loss device, 5 is a transmitter, 6 is a receiver, 8 is a power amplifier, 9 is a speaker, and 10 is a comparator. Reference numeral 11 indicates a mode/gain control section.

Claims (1)

[Claims] Using microphones and speakers as input/output sources, the gain of the transmitter and receiver signal paths is changed based on the level of audio-compatible electrical signals sent and received via the transmitter/receiver to automatically switch between speaking mode and listening mode. In an audio conference system formed by combining unit devices having a switching function, in addition to a first microphone for inputting voice speech, a second microphone for inputting background sound;
a balance amplifier that adjusts the gain of the electrical conversion outputs of the first and second microphones; and a difference device that outputs a difference between the electrical conversion outputs of the first microphone and the second microphone;
An audio conferencing device characterized in that the electrical conversion output from the second microphone and the electrical conversion output from the second microphone are adjusted by the gain of the balance amplifier and input into a subtractor to cancel out background sound.