JPS5961348A - Received sound volume variable system in telephone set - Google Patents
Received sound volume variable system in telephone setInfo
- Publication number
- JPS5961348A JPS5961348A JP17232182A JP17232182A JPS5961348A JP S5961348 A JPS5961348 A JP S5961348A JP 17232182 A JP17232182 A JP 17232182A JP 17232182 A JP17232182 A JP 17232182A JP S5961348 A JPS5961348 A JP S5961348A
- Authority
- JP
- Japan
- Prior art keywords
- signal
- receiving
- amount
- circuit
- attenuation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/58—Anti-side-tone circuits
Landscapes
- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
Abstract
(57)【要約】本公報は電子出願前の出願データであるた
め要約のデータは記録されません。(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.
Description
【発明の詳細な説明】
〔発明の４多雨分野〕
この発明は、電話機における側音を適正化して囲き取り
易くした受信音量可変方式に関するものである。DETAILED DESCRIPTION OF THE INVENTION [Four Rainy Fields of the Invention] The present invention relates to a variable reception volume system that optimizes and easily surrounds sidetones in a telephone.
従来、電話機の送話器と受話器とに増幅器を接続して、
電話機と交換機との間を結ぶ回線による伝送損失□番補
う方式を採用する電話機が用いられている。Conventionally, an amplifier is connected to the transmitter and receiver of a telephone,
Telephones are used that employ a method to compensate for transmission losses caused by lines connecting the telephone and the exchange.
また、上記の電話機における受信側の増幅器のゲインを
制御するために可変抵抗器を設けて、電話機の使用者が
適当に増幅器のゲインをコントロールするように楢成さ
れた電話機も知られている。Furthermore, there is also known a telephone set in which a variable resistor is provided to control the gain of the amplifier on the receiving side of the above-mentioned telephone set, so that the user of the telephone set can appropriately control the gain of the amplifier.
しかしながら、このような電話機における受信音量可変
方式では、受信音量を太きくしようとすると、送話器か
ら送出された送信信号が、ノ・・イブリッド回路を経由
して受話器へ戻ってし゛まうことに々す、所謂側音を大
きくするので、通話品質を劣化させることにな〕だ。However, with this type of variable receiving volume system for telephones, if you try to increase the receiving volume, the transmitted signal sent from the transmitter may return to the handset via a hybrid circuit. This increases the so-called sidetone, which degrades the quality of the call.
更に、電子式ボタン電話装置等では、交換旧から送られ
てくる直流電流は、電子式ボタン電話装置の主装置にお
いて遮断され、電話機には供給されない。このため、上
記の電流のレベル変化を回線の損失の変化として捕らえ
、これに基づき側音の大きさを自動調整する方式は採用
することができず、これに代る新らたな受信音量可変方
式の出現が要望されていた。Furthermore, in electronic key telephone devices, the direct current sent from the replacement device is cut off in the main device of the electronic key telephone device, and is not supplied to the telephone. For this reason, it is not possible to adopt a method that automatically adjusts the sidetone volume based on the above-mentioned current level change as a change in line loss. The emergence of a method was requested.
本発明は上記のような従来方式の欠点と、要望とに蚤み
てなされたものである。それ故、本発明の目的は、受話
器から出力される音量を適正化するとともに、側音につ
いても適当に防止することができる電話機における受信
音量可変方式を提供することである。The present invention has been made in view of the above-mentioned drawbacks of the conventional system and demands. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a system for varying the reception volume of a telephone, which can optimize the volume output from the handset and appropriately prevent sidetones.
そこで、本発明では、送話器から出力された送信信号を
交換機に送出し、交換機から送出された受信（，１号を
受話器へ送出する）・イブリッド回路から送られた受信
信号のレベルを変化させる受信レベル可変回路と、上記
送信信号と上記受信信号と上記受・信レベル可変回路の
出力信号とを入力し、これらの信号の大小の関係に基づ
いて、送信信号及び受信信号に対する減衰器を指示する
信号を出力する制御回路と、この制御回路の出力信号に
基づき減衰量を変化させられる送信側減衰器及び受信側
減衰器とを有し、上記受信レベル可変回路の出力が変化
することにより上記送信側減衰器及び受信側減衰器のオ
ンリフと減衰量とが変化させられるようＫして、−ト記
目的を、達成した。Therefore, in the present invention, the transmitting signal output from the handset is sent to the exchange, and the level of the receiving signal sent from the exchange (sending No. 1 to the handset) and the receiving signal sent from the hybrid circuit is changed. inputting the above-mentioned transmission signal, the above-mentioned reception signal, and the output signal of the above-mentioned reception/reception level variable circuit, and setting an attenuator for the transmission signal and the reception signal based on the magnitude relationship of these signals. It has a control circuit that outputs an instruction signal, and a transmitting-side attenuator and a receiving-side attenuator that can change the amount of attenuation based on the output signal of the control circuit, and when the output of the variable reception level circuit changes, The above objective was achieved by changing the on-riff and attenuation amount of the transmitting-side attenuator and the receiving-side attenuator.
以下１図面を参照して本発明の実施例を詳しく説明する
。Embodiments of the present invention will be described in detail below with reference to one drawing.
第１図は、本発明の方式を採用した電話機の要部ブロッ
ク図である。同図において、■は回線を示し、この回ｆ
５！１は図示せぬ交換機、寸たは１゛２］示せぬ主装置
を介して交換機と接続される。この回；腺１にはハイブ
リッド回路２が接続され、このハイブリッド回路２は、
送信信゛号が回線１仙−＼出力され、また、回線１がら
送られてきた受イ言（ｌ″ｉ号は受話器３側へ送出され
るように機能する。FIG. 1 is a block diagram of the main parts of a telephone that employs the system of the present invention. In the same figure, ■ indicates a line, and this line f
Reference numeral 5!1 is connected to an exchange (not shown), or 1.2 is connected to the exchange via a main device (not shown). This time: Hybrid circuit 2 is connected to gland 1, and this hybrid circuit 2 is
The transmitted signal signal is output from the line 1, and the received signal (l''i signal) sent from the line 1 is sent to the receiver 3 side.
この受ｎ１１器：うとハイブリッド回路２との間には、
受信側減衰器４と増幅器５とが直列にブ１−在している
。また、送話器６とノゾプリッド回路２との間には、マ
イク増幅器７と送信側減衰器８と増幅器９とが介在して
いる。Between this receiver n11 and the hybrid circuit 2,
A receiving side attenuator 4 and an amplifier 5 are connected in series. Further, a microphone amplifier 7, a transmitting side attenuator 8, and an amplifier 9 are interposed between the transmitter 6 and the nozzoprid circuit 2.
更に、ハイブリッド回路２には、チョークコイル１０１
．抵抗１０！ ＋ １０ｇ、コンデンサ１０４からなる
平衡回路網１０が接続され、回線１から外方向のインピ
ーダンスとのマツチングがとられ一定程度の（１４’ｌ
Ｖｒを防止するようになっている。Furthermore, the hybrid circuit 2 includes a choke coil 101.
．． Resistance 10! A balanced circuit network 10 consisting of +10g and a capacitor 104 is connected, and the impedance in the outward direction from the line 1 is matched to a certain degree (14'l).
It is designed to prevent Vr.
また、この実施例においては、この平ｉ１＃回路網１（
）に、コンデンサ１１、抵抗１２を介して、σ」変抵抗
１：３と抵抗１４との直列回路に電圧Ｖｃｃが与えられ
た受信レベル可変回路が接続されている。この受信レベ
ルｉ」変回路の可変抵抗１３は増幅器５のゲインをコン
トロールして、受話器３から得られる受信（、、−号レ
ベル（音？）をコントロールするようになっている。ま
た、可変抵抗１３の値が変化することにより、平衡回路
網用の特性を変化させる。つオリ、ｏＪ変抵抗１３の抵
抗値が大きくなるほど、平衡回路網１０のインピーダン
スを、近距離の端末との通話時用のインピーダンスとし
、可変抵抗１３の抵抗値が小さくなるほど、平衡回路網
用のインピーダンスを、遠距離の端末との通話時用のイ
ンピーダンスとする。In addition, in this embodiment, this flat i1# circuit network 1 (
) is connected via a capacitor 11 and a resistor 12 to a reception level variable circuit in which a voltage Vcc is applied to a series circuit of a σ" variable resistor 1:3 and a resistor 14. The variable resistor 13 of this reception level i'' conversion circuit controls the gain of the amplifier 5, and controls the reception (,, - signal level (sound?)) obtained from the receiver 3. By changing the value of 13, the characteristics for the balanced circuit network are changed.As the resistance value of the oJ variable resistor 13 increases, the impedance of the balanced circuit network 10 becomes more suitable for a call with a nearby terminal. As the resistance value of the variable resistor 13 becomes smaller, the impedance for the balanced circuit network becomes the impedance for communication with a terminal at a far distance.
また、第１図において、１５は制御回路を示す。Further, in FIG. 1, 15 indicates a control circuit.
この制御回路１５はプロセッサ機能を有するもので、受
信レベル可変回路の出力信号（可変抵抗１３を介して得
られる電圧）と、増幅器５の出力信号である受信（ｉｆ
ｆｉ号と、マイク増幅器７の出力信号である送信信号と
を人力し、これらの大小関係に基づいて、送信信号及び
受４Ｍ信号に対する減衰量を指示する信号を出力する。This control circuit 15 has a processor function, and receives the output signal of the reception level variable circuit (voltage obtained via the variable resistor 13) and the reception (if
fi signal and the transmission signal which is the output signal of the microphone amplifier 7, and based on the magnitude relationship between them, a signal indicating the amount of attenuation for the transmission signal and the received 4M signal is output.
この・１１号は受信側減衰器４と送信側減衰器８へ到り
、夫々の減衰器４，８がオン・オフされ、また、減衰量
が調整される。This No. 11 reaches the receiving-side attenuator 4 and the transmitting-side attenuator 8, and the respective attenuators 4 and 8 are turned on and off, and the amount of attenuation is adjusted.
以下、制御回路］５の機能を具体的に説明する。Hereinafter, the function of the control circuit]5 will be specifically explained.
先ず、受信側減衰器４、送信ｆｌｌｌ誠衰器８がオフの
場合、制御回路１５は、受信レベルｏＪ変回路からの出
力が、現在受（ｇされている受信信号のレベルが大きい
旨を示しているときには、受信側減衰器４の減衰量を大
きくシ、かつ送信側減衰器８の減衰量を大きくするよう
に信号を出す。つまり、１■５話機の使用者が可変抵抗
１３を調整して出力電圧が犬となるようにするから、こ
の出力電圧に応じて太きくすべき減衰量の変化分を決定
し、信号を出す。First, when the receiving side attenuator 4 and the transmitting attenuator 8 are off, the control circuit 15 causes the output from the receiving level oJ conversion circuit to indicate that the level of the receiving signal currently being received is high. When the attenuator 4 on the receiving side is attenuated, a signal is issued to increase the attenuation amount of the attenuator 4 on the receiving side and the attenuation amount on the attenuator 8 on the transmitting side. Therefore, the amount of change in the amount of attenuation to be increased is determined according to this output voltage, and a signal is output.
′また、受信レベル可変回路の出力が、現在受信されて
いる受信信号のレベルが小さい旨を示しているときには
、受信側減衰器４の減衰量を小さくし、送信側減衰器８
の減衰量を小さくする。つまり、電話機の使用者が１」
変抵抗１３を調整して出力電圧が小となるようにするか
ら、この出力電圧に心して小さくすべき減衰量の変化分
を決定し、信号を出す。'Furthermore, when the output of the reception level variable circuit indicates that the level of the reception signal currently being received is low, the amount of attenuation of the reception side attenuator 4 is decreased, and the attenuation amount of the reception side attenuator 8 is decreased.
Reduce the amount of attenuation. In other words, the number of users of the telephone is 1.
Since the variable resistor 13 is adjusted to reduce the output voltage, the amount of change in the amount of attenuation to be reduced is determined based on this output voltage, and a signal is output.
寸だ、受信側減衰器４、送（ｇ側減衰器８がオフの場合
、送信側減衰器８の減衰量は０ｄＪ１とされ、受１＾仰
［減衰器４の減衰器の変化分は、受信されている音量に
比例するようになされる。When the receiving attenuator 4 and the transmitting side attenuator 8 are off, the attenuation amount of the transmitting attenuator 8 is 0 dJ1, and the change in the attenuator of the receiving side attenuator 4 is It is made proportional to the volume being received.
史に、制御回路１５は増幅器５から出力される受信信号
と、１４２３９４幅器７から出力される送１ぎ信号とを
夫々取り込み、これらを夫々積分して、その積分値を比
較し、受信信号の積分値が送信信号の積分値よりも犬の
ときけ受信モードであるとして、受信側減衰器４、送信
側減衰器８をオフとする信号を出力し、送信信号の積分
値が受信信号の積分値よりも犬のときは送信モードであ
るとして、受信側減衰器４、送信側減衰器８をオンとす
る信号を出す。Historically, the control circuit 15 takes in the reception signal output from the amplifier 5 and the transmission signal output from the 142394 amplifier 7, integrates them, compares the integral values, and calculates the reception signal. If the integral value of the transmitted signal is higher than the integral value of the transmitted signal, it is assumed that the receiving mode is a dog, and outputs a signal that turns off the receiving side attenuator 4 and the transmitting side attenuator 8, and the integral value of the transmitted signal becomes higher than that of the received signal. If the integrated value is a dog, it is assumed that the mode is transmitting, and a signal is output to turn on the receiving attenuator 4 and the transmitting attenuator 8.
このような電話機において、通話となった場合の動作を
説明する。The operation of such a telephone when a call is made will be explained.
この電話機の１重用者は、相手の音声を受話器３から聞
いて、例えば、音、斌が小さいから太きくしようとして
可変抵抗１３の抵抗値を調整し、これによシ受信しベル
用変回路の出力電圧が小さくなったとする。A single user of this telephone listens to the other party's voice through the receiver 3, adjusts the resistance value of the variable resistor 13 to make the sound louder, for example, since the sound is small, and receives the voice through the bell conversion circuit. Suppose that the output voltage of
これにより、増幅器５のゲインが上昇され、かつ平価回
路網１０に対して遠距離用のインピーダンスとなるよう
に可変抵抗１３が働く。これにより、平価回路網１０が
ハイブリッド回路２から受話器３へ流入する側音を適当
に防止する。As a result, the gain of the amplifier 5 is increased, and the variable resistor 13 acts to provide a long-distance impedance to the equalization circuit network 10. Thereby, the equalization network 10 appropriately prevents sidetones flowing from the hybrid circuit 2 to the receiver 3.
更に、制御回路１５は可変抵抗１３から出力される電圧
が小さくされた変化分から、受信側減衰器４、送信側減
衰器８の減衰量の変化分を決定しくつ−まシ、受信音量
に正比例するように決定し）、受信側減衰器４、送信側
減衰器８の減衰量を調整する信号を出し、適当な減衰量
が設定される。Furthermore, the control circuit 15 determines the amount of change in the amount of attenuation of the receiving side attenuator 4 and the sending side attenuator 8 based on the change in the voltage output from the variable resistor 13, which is directly proportional to the receiving volume. A signal is output to adjust the amount of attenuation of the receiving-side attenuator 4 and the transmitting-side attenuator 8, and an appropriate amount of attenuation is set.
一方、制御回路１５は、上記動作に並行して増幅器５か
ら受信信号を入力し、マイク増幅器７から送信信号を入
力し、これらの積分値から受信モードか送信モードか判
定する。On the other hand, the control circuit 15 inputs the received signal from the amplifier 5 and the transmitted signal from the microphone amplifier 7 in parallel with the above operation, and determines whether the mode is the receiving mode or the transmitting mode from these integral values.
今、相手側が話をしているとすると、受信信号の積力値
が送信４Ｗ号の積分値より犬となシ、制御回路１５は、
受信側減衰器４；送信側減衰器８をオフとする（Ｍ号を
出す。すると、送信側減衰器８の減衰１ｔは０ｄ１３と
なり、受信側減衰器４の減衰量は上ＭＬ軸動作制御回路
］５が設定した量となる。この受イト（τ１１ｊ減哀器
４の減衰量は、相手側グｈ１末の距離に対して十分に少
なく、シかも、受信信号は増幅器５で増幅され受話器３
に到るから、十分に聞き取り可能である。Now, if the other party is talking, the product value of the received signal is greater than the integral value of the transmitted 4W signal, and the control circuit 15
Receiving side attenuator 4; Transmitting side attenuator 8 is turned off (M signal is output. Then, the attenuation 1t of the transmitting side attenuator 8 becomes 0d13, and the attenuation amount of the receiving side attenuator 4 is determined by the upper ML axis operation control circuit. ] 5 becomes the set amount.The amount of attenuation of this receiver (τ11j) is sufficiently small compared to the distance from the other party's terminal h1, and the received signal is amplified by the amplifier 5 and sent to the receiver 3.
, so it is fully audible.
上記に替わって、この電話機の使用者が話を開始すると
、送信信号の積分値が受（ｇ信号の積分値より犬となり
、これにより、制御回路１５は受信側減衰器４、送信側
減衰器８をオンとする。これにより、送信側減衰器８、
受信側減衰器４は夫々、上記制御回路１５の動作で設定
された減衰量を有することになる。例えば、送信側減衰
器８の減衰量が６ｄＢとされ、受信側減衰器４の減衰量
がオフ時の減衰量に６ｄＢ加えた減衰器とされる。Instead of the above, when the user of this telephone starts talking, the integral value of the transmitting signal becomes smaller than the integral value of the receiving (g) signal, so that the control circuit 15 8 is turned on.As a result, the transmitting side attenuator 8,
Each of the receiving side attenuators 4 has an attenuation amount set by the operation of the control circuit 15 described above. For example, the attenuation amount of the transmitting side attenuator 8 is set to 6 dB, and the attenuation amount of the receiving side attenuator 4 is set to be 6 dB added to the attenuation amount when the receiving side attenuator 4 is off.
このため、送信信号がハイブリッド回路２を介して送出
されるときには減衰量として６ｄＢであるのに対し、こ
の送イご信号がノ・イブリッド回路２から受話器：３へ
回シ込む側廿は、受信（ｆ！！ｌ減衰器４により更に６
ｄＢ減哀される。Therefore, when the transmission signal is sent out via the hybrid circuit 2, the amount of attenuation is 6 dB, but when this transmission signal is routed from the hybrid circuit 2 to the receiver 3, the reception (Additionally 6 by f!!l attenuator 4
dB is reduced.
このため、側音１ｕｔ（！：んど防止されることになる
。For this reason, the sidetone 1ut (!:) is almost prevented.
以上説明したように、本発明によれば、受話器から得ら
れる側音は、可変抵抗の操作に、ｌ−り適正化されると
ともに、この司ダ抵抗の作用によ（９平衡回路網の・ｒ
ンピーダンスが変化し、かつ、適宜な減衰１ｊ、が、受
イぎ信号のルート及び送信信号のルートに与えられるか
ら、側廿も嫡当に防市される。As explained above, according to the present invention, the sidetone obtained from the handset is optimized by the operation of the variable resistor, and by the action of the conductor resistor (9-balanced circuit network). r
Since the impedance changes and appropriate attenuation 1j is applied to the route of the received signal and the route of the transmitted signal, the sidewalls are also properly protected.
第１図は本発明の方式を適用した電話機の要部ブロック
図である。
■・・・回 線
２・・・ハイブリッド回路
３・・・受話器
４・・・受信側減衰器
５．９・・・増幅器
６・・・送話器
７・・・マ・ｆり増幅器
七（・・・送信側減衰器
１（Ｊ・・・平衡回１ｉ′ｉ；網
（１３、１４）・・・受信レベル可変回路］５・・・制
御回路FIG. 1 is a block diagram of the main parts of a telephone to which the system of the present invention is applied. ■... Line 2... Hybrid circuit 3... Receiver 4... Receiving side attenuator 5.9... Amplifier 6... Transmitter 7... Ma/f amplifier 7 ( ... Transmission side attenuator 1 (J... Balance circuit 1i'i; network (13, 14)... Reception level variable circuit] 5... Control circuit
Claims (3)
出し、父換機から送出された受信信号を受話器へ送出す
るハイブリッド回路から送られた受信信号のレベルを変
化させる受信レベル可変回路と、 前記送信信号と前記受信信号と前記受信レベル可変回路
の出力信号とを入力し、これらの信号の大小関係に基づ
いて、前記送信信号及び前記受信信号に対する減衰量を
指示するＩｂ号を出力する制御回路と、 該制御回路の出力信号に基づき減衰量が変化させられる
送信側減衰器及び受信側減衰器とを有し、 前記受信レベル可変回路の出力が変化することにより、
前記送信側減衰器及び前記受信側減衰器のオン・オフと
減衰量とが変化させられることを特徴とする電話機にお
ける受信音量可変方式。(1) A reception level variable circuit that changes the level of the reception signal sent from a hybrid circuit that sends the transmission signal output from the handset to the exchange and the reception signal sent from the father exchange to the receiver. , inputting the transmission signal, the reception signal, and the output signal of the reception level variable circuit, and outputting a signal Ib indicating an attenuation amount for the transmission signal and the reception signal based on the magnitude relationship of these signals. It has a control circuit, and a transmitting-side attenuator and a receiving-side attenuator whose attenuation is changed based on the output signal of the control circuit, and when the output of the reception level variable circuit changes,
A receiving volume variable system for a telephone set, characterized in that on/off and attenuation amount of the transmitting side attenuator and the receiving side attenuator are changed.
の平衡回路網の特性を変化させることを特徴とする特許
請求の範囲第１項記載の電話機における受信音量可変方
式。(2) The receiving volume variable system in a telephone set as claimed in claim 1, wherein the receiving level variable circuit is connected to a balanced circuit network and changes the characteristics of this balanced circuit network.
、受信されている音振に比例して決定され、送信モード
時に受信されている音量に反比例して決定され、送信側
減衰器の減衰量の変化分は送信モード時に受信されてい
る音量に反比例して決定されることを特徴とする特許請
求の範囲第１項又は第２項記載の電話機における受信音
量可変方式。(3) The amount of change in the amount of attenuation of the receiving attenuator is determined in reception mode in proportion to the sound vibration being received, and in the transmission mode in inverse proportion to the received sound volume. 3. The receiving volume variable system for a telephone set according to claim 1 or 2, wherein the amount of change in the amount of attenuation is determined in inverse proportion to the volume being received during the transmission mode.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP17232182A JPS5961348A (en) | 1982-09-30 | 1982-09-30 | Received sound volume variable system in telephone set |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP17232182A JPS5961348A (en) | 1982-09-30 | 1982-09-30 | Received sound volume variable system in telephone set |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPS5961348A true JPS5961348A (en) | 1984-04-07 |
Family
ID=15939741
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP17232182A Pending JPS5961348A (en) | 1982-09-30 | 1982-09-30 | Received sound volume variable system in telephone set |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS5961348A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5321746A (en) * | 1991-02-28 | 1994-06-14 | Motorola, Inc. | Adjustable gain range current mirror |
| US5790657A (en) * | 1995-01-26 | 1998-08-04 | Nec Corporation | Echo suppressor capable of suppressing an echo resulting from acoustic coupling without spoiling a natural sound of conversation |
-
1982
- 1982-09-30 JP JP17232182A patent/JPS5961348A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5321746A (en) * | 1991-02-28 | 1994-06-14 | Motorola, Inc. | Adjustable gain range current mirror |
| US5790657A (en) * | 1995-01-26 | 1998-08-04 | Nec Corporation | Echo suppressor capable of suppressing an echo resulting from acoustic coupling without spoiling a natural sound of conversation |
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