JPS58179046A - Conference telephone device - Google Patents

Abstract

PURPOSE:To prevent great deterioration of the S/N of sending speech output due to noises, by varying automatically the gain frequency characteristics of a speech sending path in response to the noise level so that a proper S/N is always secured. CONSTITUTION:The speaker's voices are collected to a microphone 5 and amplified by a preamplifier 3 to be applied to a noise level detecting part 1 and a filter part 2. The audio signal is supplied to a rectifying and charging/discharging circuit 12 at the part 1. The circuit 12 is set so as to have a large charging time constant and a small discharging time constant. Thus the audio signal having its amplitude changing suddenly on the time axis is not charged; while the charging voltage corresponding to the noise level is delivered to a level deciding circuit 13 for the steady noise having its amplitude changing slowly on the time axis. Then the circuit 13 delivers a level deciding signal corresponding to the charging potential to a control circuit 14. The circuit 14 delivers a binary signal in response to the noise level and has the filter characteristics when the signal is set at ''1'' and has no filter characteristics when the signal is set at ''0'', respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a conference telephone device that is equipped with a microphone and a speaker and transmits and receives audio signals to and from a subscriber on the other side during a conference.

[Description of prior art]

In conventional conference telephone devices, the means for transmitting the sound and signal of the speech to the subscriber on the other end is to amplify the voice signal of the speech collected by a microphone to the line level using an amplifier circuit. Therefore, if the indoor noise level of the room in which the conference telephone device is used reaches a level that interferes with telephone calls, the 8N ratio (ratio of the spoken voice level to the indoor noise level) of the transmitted voice will become small. This has the disadvantage that the clarity of the voice received by the other subscriber is significantly degraded, making it difficult to communicate.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a conference telephone device whose call performance is not significantly degraded by indoor noise.

[Key points of the invention]

The present invention relates to a conference telephone device in which a microphone and a speaker are installed in one room, and conference participants in the room can talk to distant parties, and the present invention is concerned with the indoor noise level of the room where the conference phone device is installed. 2.The noise level detection section generates a control signal corresponding to the magnitude of the indoor noise level, and receives the vibration signal from the bell detection section, and the attenuation characteristics change according to the control signal. By equipping the transmitting circuit with a filter unit, even when the human power of the transmitter is mixed with the steady room noise output, it is possible to make calls during a conference without significantly deteriorating the 8N ratio of the transmitter's output due to the noise output. It has been made possible.

[Explanation of Examples]

Embodiments of the present invention will be described with reference to the accompanying drawings. @
Figure 1 is a block configuration diagram of an embodiment of the present invention, Figure 2 is a detailed block diagram of the main circuitry constituting the above embodiment of the invention, and the wcs diagram is a power spectrum characteristic diagram of HOth noise. be.

FIG. 4 is a characteristic diagram of a bypass filter according to an embodiment of the present invention. Drawing number IFi noise level detection unit in Figure 1, 2i
j filter section, 3 is preamplifier, 4 is transmitting amplifier, 5t
i microphone, 6Fi transmitting line end, 7Fi speaker,
8 is a receiver amplifier, and 9ti is a receiver line end. The component lO of the filter section 2 in FIG. 2 has a reduction in attenuation of approximately 2.
dB/octave active bypass filter, the same <11 is a 44B/octave active bypass filter, the component part 12 of the noise level detection section l is a rectifier charge/discharge circuit, and the same <13 is a level determination circuit. , is also a 14Fi control circuit.

tl! In FIGS. 1 and 2, speech is collected by a microphone 5, amplified by a preamplifier IK, and then provided to a noise level detection section 1 and a filter section 2. The audio signal supplied to the noise level section IK is supplied to the input of a rectifier charging/discharging circuit 12 constituting the noise level detecting section 1. The rectifier charge/discharge circuit is configured to have a large charging time constant and a small discharging time constant. Due to this charging/discharging characteristic, it is possible to respond to sound signals whose amplitude changes rapidly on the time axis without charging, and to respond to steady noise whose amplitude changes slowly on the time axis according to the noise level. The charged voltage is output to the level determination circuit 13. Based on the relationship between the charging voltage of the rectifier charging/discharging circuit 12 and the noise level, the level determination circuit 13 sends a level determination signal corresponding to the charging potential given from the rectifying charging/discharging circuit 12 to the control circuit 14.
Output to. The function of the level determination circuit 13 is that the potential of the rectifying charge/discharge circuit 12 corresponds to the noise level, so if the noise level is determined based on the potential and a determination signal corresponding to the noise level is generated, K is obtained. When the noise level is 55 phon or less, the level judgment circuit 13
In the case of the signal f56~40 phone, the second signal is 41~
In the case of 45 phones, the fifth signal is output.In the case of 46 phones or more, the signal of tube 4 is output.

Next, the filter section 2 provided in the transmission path will be explained. The filter section 2t-constituting the 2 6B octave active bypass filter 10 and the 4 dB active bypass filter 11 operate so that the filter characteristics change according to the control signal of the control circuit 140, so that the signal given from the control circuit 14 is a binary signal. When it is "1", it operates to have filter characteristics, and when the signal given from the control circuit 14 is a binary signal "0", it operates so that it does not have filter characteristics.

Here, the characteristics of each filter constituting the filter section 2 will be explained. In general, indoor noise in a conference room is Hoth noise as shown in FIG. 3, so components whose noise level interferes with telephone calls are abundant in low frequencies and very few in high frequency regions.

From this, as a method to prevent the degradation of the transmitting Ell ratio due to noise, it is possible to reduce it by filter characteristics such as 2 (lB, 4 dB%, 6 dB, etc.) depending on the total noise level at low frequencies below 1 kHz. This is desirable.

When the signal given from the control circuit 14#i level determination circuit 13 is the first signal, that is, the noise level is 35 phon or less, the 2 dB/octave active bypass filter 10 and 4 eLn/y+-octave active bypass filter ll are , a binary signal "0" is given, and the characteristics of each filter 10 and 11 are summed to have a flat characteristic. Further, when the signal given from the level determination circuit 13 is the second signal, that is, the noise level is 56 to 40 phona, the binary signal "1" is sent to the filter 10, and the binary signal "0" is sent to the gold filter 11. so that the characteristic of the filter section 2 becomes a bypass filter of 2 aB/octave.

When the signal given from the level judgment circuit 13 is the sixth signal, that is, the noise level is 41 to 45 phon, the binary signal "0" is applied to the filter IOK, and the binary signal "1" is given to the filter IIK. The characteristic of section 2 is set to be a bypass filter of 411B/octave. The signal given from the level judgment circuit 13 is the fourth
When the signal, that is, the noise level is 46 phon or more, a binary signal "1" is given to both the filter IO1 and the filter IIK, and the filter part 2 is operated as a bypass filter with a characteristic of baB/octave. Next, the receiving line will be described. The voice signal from the other party provided to the receiving line end 9 is power amplified by the receiving amplifier 8, and is applied to the speaker 7, where it is amplified.

The filter section 2 described in the above embodiment is a means for changing the attenuation characteristics of the filter according to the noise level, but in line with the gist of the present invention, by using means for changing the cutoff frequency of the filter section, the same effect can be achieved. It can be implemented.

In the above example, the noise level detection unit 1 is configured to obtain an input signal from the detection output of the microphone 5 for telephone calls, but it is not limited to this microphone, but may be any other sound collection means for detecting noise in the room. may also be used.

[Explanation of effects]

As explained above, the conference telephone device of the present invention automatically adjusts the gain frequency characteristics of the transmission path according to the noise level to ensure an appropriate 8M ratio under normal pressure even during steady noise during a conference. However, it is possible to ensure speech quality during a conference without significantly degrading the 8M ratio of the transmitting speech output due to noise.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention. FIG. 2 is a detailed block diagram of the main circuitry that constitutes the same as above. FIG. 5 is a power spectrum characteristic diagram of U-Hoth noise. FIG. 4 is a characteristic diagram of a bypass filter according to an embodiment of the present invention. ■...Mf level detection section, 2...filter section, 3.
...Preamplifier, 4...Talking amplifier, 5...Microphone, 6...Talking line end, 7...-Speaker, 8.
... Receiving amplifier, 9... Receiving line end, lO... 2d
B/octave active bypass filter, 11...
・4 dB/octave active bypass filter,
12... Rectifier charge/discharge circuit, 13... Level determination circuit, 14... Control circuit. Patent Applicant NEC Corporation Representative Patent Attorney Takaji Ide 1 Figure 7 Frequency random number, (kHz) Figure 3

Claims (1)

[Claims] (1) -f A microphone and a speaker are placed in the same room, and the conversation in the room detected by the microphone is transmitted to a distant subscriber, and the voice of this distant subscriber is transmitted to the speaker. In the conference telephone device configured as above, a noise level detection section detects a component whose amplitude changes slowly on a time axis among the signals detected by the microphone or another sound collecting means provided in the room; and a filter section that changes attenuation characteristics according to the detection output of the noise level detection section, and the filter section is inserted into an output path of the microphone.