Communication device and audio signal transmission method

Abstract

To prevent click noise due to catching of an operation sound of a PTT switch by a microphone in a communication apparatus which can perform transmission with the depression of the PTT switch.SOLUTION: A microphone type detector 43 detects the structural relationship between a microphone and a PTT switch used for transmission, elongates the buffer length (increases the capacity) of a variable length buffer 124 when the microphone is in the structural relationship of catching an operation sound of the PTT switch like an external microphone, and shortens the buffer length (reduces the capacity) when there is no possibility of catching the operation sound. When the PTT switch is released, with the releasing timing as a reference, mute circuits 1811-181n perform a mute operation to an audio signal of the variable length buffer 124 thereafter. Consequently, the possibility in which a talk (transmission) becomes unfinished is reduced when there is no problem due to the structure while preventing the occurrence of grating click noise.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method and device for transmitting an audio signal in a communication device in which transmission is enabled by pressing a press-to-talk switch, and which prevents the operating sound that may be generated when the press-to-talk switch is released from being reproduced as a pop sound on the receiving side. [Background technology]

[0002] In communications devices that transmit by pressing a press-to-talk switch (also known as a PTT switch, hereafter referred to as a PTT switch) used in walkie-talkies, intercoms, videoconferencing systems, and other devices, if the microphone and PTT switch are located close to each other, the microphone can pick up the sound of the PTT switch being released. When the PTT switch is released and the sound is demodulated on the receiving device, a popping noise can be generated from the speaker, causing an unpleasant noise for the receiving device. Specifically, when the sender attempts to stop transmitting and begins to release their finger from the PTT switch, the sound of the lever pressing the switch sliding and the sound of the spring inside the switch returning are generated. However, the switch contacts are not yet broken, and the communications device continues transmitting. Therefore, these operating sounds are picked up and transmitted by the microphone. Subsequently, the switch contacts are broken, disconnecting the PTT line. The control and audio signal processing circuits detect the PTT disconnection, and the communications device stops transmitting. Therefore, since the operating sound is generated before the PTT line is disconnected, it is difficult to prevent the generated operating sound from being transmitted.

[0003] In the case of intercoms and video conference systems, the microphone is often mounted on the main unit and in the same housing as the PTT switch, but the housing is relatively large, so it is easy to take structural measures to reduce the operating noise, such as by devising a microphone mounting structure.In the case of portable radios, the housing is small, but the microphone and PTT switch are separated to a certain extent, and in terms of structure, it is possible to use a relatively expensive PTT switch that is highly reliable and has smooth operation.

[0004] On the other hand, if the microphone is an external microphone equipped with a PTT switch, it is small because the user holds it in their hand or attaches it to their collar, etc. As a result, the microphone and PTT switch are close to each other, and the operating noise travels through the housing and reaches the microphone. In other words, it is difficult to structurally block the transmission of the operating noise. Furthermore, an external microphone is an accessory (optional) part, and compared to the PTT switch on the radio itself, it is necessary to use a relatively inexpensive part, and the operating noise itself is also louder.

[0005] Therefore, the present applicant has proposed a typical prior art pop noise reduction device in Patent Document 1. In this prior art, in a digital radio, a transmission audio signal is buffered and transmitted, and when the PTT switch (transmission / reception switching means) is switched to the release position (transmission stopped), data from the time of switching up to a predetermined time before is replaced with silent data, thereby preventing the operating noise from being reproduced on the receiving side and becoming a pop noise. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5343843 Summary of the Invention [Problem to be solved by the invention]

[0007] The above-mentioned conventional technology is effective in suppressing popping noise. However, because it replaces the data from the time the PTT switch is switched until a certain time before with silent data, if the PTT switch is released immediately after finishing a call, the final part of the call may be masked, causing the end of the call to be cut off. Furthermore, to reliably suppress popping noise, it is necessary to set a long period for buffering the transmitted audio signal, which increases the transmission delay between the transmitter and receiver. On the other hand, as mentioned above, there are cases where popping noise does not necessarily need to be taken into consideration, such as when the PTT switch and microphone are far apart.

[0008] The object of the present invention is to provide a communication device and a voice signal transmission method that can reduce transmission delay while preventing the occurrence of popping sounds on the receiving side caused by the operating sound generated when the press-to-talk switch is released. [Means for solving the problem]

[0009] The communication device of the present invention is a communication device that enables transmission by pressing a press-to-talk switch, and comprises: detection means for detecting the structural relationship between a microphone used for transmission and the press-to-talk switch; variable-capacity storage means for temporarily storing an audio signal picked up by the microphone; transmission means for modulating the audio signal temporarily stored in the storage means in a predetermined modulation mode and transmitting the modulated audio signal; and control means for detecting the pressing or release of the press-to-talk switch, wherein the control means sets the capacity of the storage means based on the detection result of the detection means, and upon detecting the release of the press-to-talk switch, notifies the transmitting means of this, and the transmitting means mutes the audio signal temporarily stored in the storage means when the press-to-talk switch is released.

[0010] Furthermore, the voice signal transmitting method of the present invention is a method for transmitting a voice signal of a communication device that enables transmission by pressing a press-to-talk switch, and is characterized by including the steps of: detecting a structural relationship between a microphone used for transmission and the press-to-talk switch; presetting the capacity of a variable capacitance storage means based on the detection result; temporarily storing a voice signal collected by the microphone in the storage means; modulating the voice signal temporarily stored in the storage means in a predetermined modulation mode and transmitting the modulated voice signal; and muting the voice signal temporarily stored in the storage means in response to the release of the press-to-talk switch and transmitting the muted voice signal.

[0011] According to the above configuration, in communications equipment that enables transmission by pressing a press-to-talk switch, such as a walkie-talkie, intercom, or video conference system, depending on the relative positions of the microphone used for transmission and the press-to-talk switch, the microphone may pick up the operating sound of the press-to-talk switch when it is released, and when the receiving side demodulates this, a popping sound will be generated from the speaker. Therefore, the detection means first detects the structural relationship between the microphone used for transmission and the press-to-talk switch, and if the structural relationship is such that the operating sound of the press-to-talk switch is picked up, the control means causes the transmission means to mute the audio signal for the period during which the operating sound is generated, based on the timing of the release of the press-to-talk switch.

[0012] Specifically, the audio signal collected by the microphone is temporarily stored in a variable-capacity storage means, and then modulated and transmitted from the transmission means in a predetermined modulation mode. The control means controls the transmission means to transmit or stop transmission (switch to reception) when it detects the pressing or release of a press-to-talk switch. The control means also presets the capacity of the storage means based on the detection result of the detection means. When the control means detects the release of the press-to-talk switch, it notifies the transmission means, which then mutes the audio signal read from the storage means.

[0013] Therefore, if the structure is such that the microphone picks up the operating sound of the press-to-talk switch when it is released, the capacity of the variable capacitance storage means is increased and, based on the release timing of the press-to-talk switch, muting is performed for the period during which the operating sound is being generated, thereby preventing the transmission of the harsh operating sound; if there is no possibility of picking up the operating sound, the capacity of the variable capacitance storage means can be minimized, thereby reducing the possibility of the talk (transmission) being cut off.

[0014] Furthermore, the communication device of the present invention is a radio, and is characterized in that when the detection means determines that the microphone is an external microphone equipped with the press-to-talk switch, the control means relatively increases the capacity of the storage means, and when the detection means determines that the microphone is not equipped with the press-to-talk switch or is a built-in microphone, the control means relatively decreases the capacity of the storage means.

[0015] According to the above configuration, in the case of the intercom or video conference system, the microphone is often built into the main unit and is often installed in the same housing as the press-to-talk switch. This relatively large housing makes it easy to structurally address the operating noise. Portable radios also have small housings, but structural measures are still possible to some extent. However, when the microphone is an external microphone equipped with a press-to-talk switch, the microphone and the press-to-talk switch are close to each other, making it structurally difficult to address the operating noise. Therefore, in such cases, the capacity of the variable capacitance storage means is relatively increased, thereby relatively increasing the amount of audio signal muted when the press-to-talk switch is released.

[0016] Therefore, in the case of a small external microphone equipped with a press-to-talk switch, which is structurally difficult to address, it is possible to take effective measures to reduce the operating noise.

[0017] Furthermore, the communication device of the present invention is a radio, wherein the transmitting means has a plurality of modulation modes, and when the detecting means determines that the microphone is an external microphone equipped with the press-to-talk switch, the controlling means further changes the capacity of the memory means according to the modulation mode.

[0018] According to the above configuration, if the microphone is an external microphone that may pick up the operating sound of the press-to-talk switch, the control means further varies the capacity of the variable capacitance storage means, i.e., the amount of audio signal to be muted, depending on the modulation mode of the transmission means.

[0019] As mentioned above, the transmission path for audio signals can be wired or wireless, and can be analog or digital. However, especially in the case of analog FM radio, the S / N ratio is approximately 40 to 50 dB, and even when there is no sound, a hissing noise remains. When the press-to-talk switch is released to end the call, the transmission signal stops, which in turn stops the operation of the low-frequency amplifier in the receiving circuit and the residual noise, thereby enabling the call to be recognized as ended. Therefore, there is no need to recognize the call ending by the popping sound; eliminating the unpleasant popping sound is particularly effective in the case of analog FM radio modulation. Thus, it is preferable to change the capacity of the variable capacitance storage means, i.e., the amount of audio signal to be muted, depending on the modulation mode. [Effects of the Invention]

[0020] As described above, in the communications device and audio signal transmission method of the present invention, in communications devices that enable transmission by pressing a press-to-talk switch, when the microphone used for transmission is structurally in a position where it picks up the operating sound of the press-to-talk switch, the audio signal picked up by the microphone is temporarily stored and muted for the period during which the operating sound is generated, based on the timing of the release of the press-to-talk switch.

[0021] Therefore, if the structure is such that the microphone picks up the operating sound of the press-to-talk switch when it is released, the operating sound can be muted to prevent the generation of an unpleasant popping sound on the receiving side.If there is no possibility of picking up the operating sound, delays due to temporary storage can be minimized and the possibility of the talk (transmission) being cut off can be reduced. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a perspective view of a radio that is a communication device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a block diagram showing the electrical configuration of the radio and the external microphone. [Figure 3] 1 is a functional block diagram for explaining an audio signal transmission method according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0023] FIG. 1 is a perspective view of a radio 1, a communication device according to an embodiment of the present invention. This radio 1 is a handheld radio. An external microphone 2 can be connected to this radio 1 by removing a connector cover on the right side 1001 of the housing 10. A power / volume knob 12, a channel selector knob 13, and an antenna 14 are provided on the top 1002 of the housing 10. A PTT switch 15 and two side switches 16 are provided on the left side 1003 of the housing 10. A display 17 and various operation keys 18, as well as a speaker 19 and a microphone 20, are provided on the front 1004 of the housing 10. The display 17 displays the transmission and reception frequencies and signal levels. A battery pack and a clip for attachment to a user's waist belt are provided on the back of the housing 10. The side switch 16 can also be used as a PTT switch for a sub-channel.

[0024] The external microphone 2 of this embodiment includes a speaker 21, a microphone 22, and a PTT switch 23. It is connected to the radio 1 via a curled cord 24 and a connector 25. The connector cover of the radio 1 is removed to expose the connector, and one end of the connector 25 is hooked onto the connector, and the other end of the connector is screwed in to connect the terminals.

[0025] FIG. 2 is a block diagram showing the electrical configuration of the radio 1 and the external microphone 2. FIG. 2 shows only the wireless communication section, and omits parts unrelated to the present invention, such as displays. The radio 1 uses the 150 MHz band and supports dual modes: a digital mode that uses 4-level FSK modulation to obtain clear sound quality, and an analog mode that uses FM modulation to easily achieve compatibility with conventional devices. The modulation method for the digital mode is not limited to 4-level FSK modulation, and the modulation method for the analog mode is not limited to FM modulation. Furthermore, the dual mode of digital and analog modes is not necessarily required, and multiple modulation methods are not necessarily supported.

[0026] The signal received by the antenna 14 is input from the transmission / reception switch 101 to the high frequency signal amplifier 102, where it is amplified, and then mixed with a local oscillation signal from the high frequency signal generator 104 in the frequency converter 103, where it is converted into an intermediate frequency signal. After that, it is converted into a digital signal in the analog / digital converter 105, and then demodulated by the demodulators 1111-1111 selected by the input / output switches 112 and 113. n The demodulator 111 is adapted to modulation modes such as the digital mode and analog mode, and either mode is selected by switches 112 and 113 in accordance with a setting from a mode setter 42 of the control unit 4, which will be described later, to decode the audio signal. The decoded audio signal is decoded into an analog audio signal by a digital / analog converter 114, amplified by a low-frequency amplifier 115, and then emitted from the speaker 19.

[0027] On the other hand, the audio signal collected by the microphone 20 is amplified by a low frequency amplifier 121, converted into a digital signal by an analog / digital converter 122, and output to AF (Audio Frequency) processors 1311 to 1312, which are selected by input / output switches 132 and 133. n (hereinafter, when collectively referred to, they are indicated by the reference numeral 131) performs processing such as upsampling and filtering, and then the signals are output to the baseband processors 1411 to 1414. n(hereinafter, when collectively referred to, they will be referred to by reference numeral 141) performs baseband signal processing according to the modulation mode selected. The processed baseband signal is converted to an analog signal by a digital / analog converter 151, and a frequency modulator 152 frequency-modulates the local oscillation signal from the high-frequency signal generator 104 to become a transmission signal, which is amplified by a power amplifier 154 and then transmitted from the antenna 14 via the transmission / reception switch 101. The components subsequent to the switch 132 constitute a transmission means.

[0028] The switches 112 and 113, the demodulator 111, the switches 132 and 133, the AF processor 131, and the baseband processor 141 are configured in a modulation / demodulation circuit including a DSP, an FPGA, etc. The frequency modulator 152 is changed depending on the selected modulation method. For example, if a digital phase modulation method is selected, it becomes a phase modulator using a quadrature modulator, and if an amplitude modulation method is selected, it becomes an amplitude modulator.

[0029] An external microphone 2 can be connected to the radio device 1 of this embodiment via a connector 25. A headset equipped with a microphone 31 for wireless communication or the like can also be used. Therefore, for these microphones 22, 31, low-frequency amplifiers 161, 171 and analog-to-digital converters 162, 172 corresponding to the low-frequency amplifier 121 and analog-to-digital converter 122 are also provided, and these are alternatively selected by a selector 123 and connected to a switch 132.

[0030] Similarly, the speaker 21 of the external microphone 2 can be used for the speaker 19, and a selector 116 is interposed between the low-frequency amplifier 115 and these speakers 19, 21. The PTT switch 23 of the external microphone 2 or a PTT switch 32 via wireless communication or the like can be used for the PTT switch 15 (16), and both are input to a PTT detector 41 in the control unit 4.

[0031] The control unit 4 controls the operation of the radio device 1, such as transmission and reception, and the mode setting unit 42 selects the switches 112 and 113, the demodulator 111, the switches 132 and 133, the AF processor 131, and the baseband processor 141 as described above, depending on the modulation method (4-ary FSK modulation or FM modulation) and the channel setting set by operating the operation keys 18 (see Figure 1).

[0032] It is noteworthy that in the radio 1 of this embodiment, the control unit 4 is provided with a microphone type detector 43 that detects the setting of the microphone type setting unit 27 provided on the external microphone 2 side. The microphone type detector 43 and the microphone type setting unit 27 constitute detection means and cooperate to detect the structural relationship between the microphone 22 and the PTT switch 23 of the external microphone 2. Specifically, it determines whether the microphone 22 of the external microphone 2 picks up the operating sound of the PTT switch 23. For this detection (determination), a dedicated signal line may be provided on the curled cord 24 and a dedicated terminal may be provided on the connector 25, or the terminals of the PTT switch 23 and the microphone 22 may be opened (high impedance), pulled up to a predetermined voltage, or preset from the operation key 18.

[0033] The microphone type detector 43 detects (determines) whether the external microphone 2 is a standalone microphone or whether it is equipped with a PTT switch 23, and if it is equipped with the PTT switch 23, whether it is provided in the middle of the curled cord 24 so as not to pick up the operating sound of the PTT switch 23, or whether the PTT switch 23 and microphone 22 are provided in the housing 28 so as to structurally pick up the operating sound of the PTT switch 23. The PTT detector 41 determines whether the built-in microphone 20, the external microphone 22, or the extension microphone 31 for wireless communication or the like is being used in response to the operation of the corresponding PTT switch 15 (16), 23, 32.

[0034] It should also be noted that in the radio device 1 of this embodiment, a variable-length buffer 124, which is a variable-capacity storage means, is interposed between the selector 123, which is the output stage of the audio signal collected by any of the microphones 20, 22, and 31, and the switch 132, which is the input stage of the transmission means, and the AF processors 1311 to 1312 are also interposed between the selector 123, which is the output stage of the audio signal collected by any of the microphones 20, 22, and 31, and the switch 132, which is the input stage of the transmission means. n and baseband processors 1411 to 141 n Between them, mute circuits 1811 to 181 n (Hereinafter, when these are collectively referred to, they will be referred to by the reference numeral 181). The variable length buffer 124 can be set to a variable length, and temporarily stores, delays, and outputs an audio signal for a period of time corresponding to the set buffer length. The control unit 4, which is a control means, is provided with a delay amount determination table 44 for setting the buffer length, i.e., the delay time.

[0035] The delay amount determination table 44 determines an appropriate buffer length from the table in response to the settings of the PTT detector 41 and mode setting unit 42 and the detection result of the microphone type detector 43, and sets the appropriate buffer length in the variable length buffer 124. Specifically, the delay amount determination table 44 first leaves the buffer length of the variable length buffer 124 at its minimum when the PTT detector 41 does not detect the PTT switch 23, i.e., when the built-in microphone 20 or the extension microphone 31 is used. Next, when the PTT detector 41 detects the use of the PTT switch 23, the delay amount determination table 44 determines that the external microphone 20 of the external microphone 2 is being used, and further sets the buffer length of the variable length buffer 124 as follows, based on the detection (determination) result of the microphone type detector 43.

[0036] The delay amount determination table 44 switches the buffer length as follows in response to the detection result of the microphone type detector 43, depending on the setting of the mode setting unit 42. That is, if the external microphone 2 is a standalone microphone only, the buffer length is minimized. On the other hand, if the external microphone 2 has a PTT switch 23, and the PTT switch 23 and microphone 22 are integrally mounted on the housing 28 and the operating sound of the PTT switch 23 is picked up due to the structure, the delay amount determination table 44 sets the buffer length to the minimum length that does not pick up the operating sound. Also, if the external microphone 2 has a PTT switch 23 but is mounted on the curled cord 24 and does not pick up the operating sound of the PTT switch 23, or if the PTT switch 23 and microphone 22 are integrally mounted on the housing 28 but the operating sound of the PTT switch 23 is not picked up due to the structure, the delay amount determination table 44 sets the buffer length to the minimum or a predetermined buffer length other than the minimum.

[0037] The delay amount determination table 44 may determine the buffer length according to the setting contents of the mode setting unit 42 and the structural relationship between the PTT switch 23 and the microphone 22, as described above. In other words, if multiple external microphones 2 with different mechanical structures can be connected to the radio 1, the time difference between when an operating sound is generated and when the PTT switch 23 is completely turned off will differ depending on the difference in the mechanical structure, and the buffer length may be determined based on this time difference.

[0038] Furthermore, the delay determination table 44 further adjusts the buffer length, i.e., the delay time, depending on the settings of the mode setting unit 42, taking into account the processing delay and additional functions of the AF processor 131 at the downstream stage. Specifically, this adjustment depends on the difference between the analog mode and the digital mode, the presence or absence of a noise canceller or equalizer, and so on. As described above, the radio device 1 of this embodiment has two modes: a digital mode using a 4-level FSK modulation method and an analog FM modulation mode. However, the application of the present invention is not limited to these two modes. For example, digital phase modulation and amplitude modulation methods are also possible. When one of these modulation methods is selected, the processing time of the AF processor 131 varies depending on the selected modulation method. Therefore, the delay determination process of the delay determination table 44 selects a time that minimizes the delay time and does not transmit operating sounds, based on the combination of the processing time of the selected modulation method and the type of microphone detected by the microphone type detector 43. The selected delay time is set as the length of the variable-length buffer 124.

[0039] When the PTT switches 15 (16), 23, and 32 are released, the PTT detector 41 causes the mute circuit 181 to perform a mute operation, muting the audio signal from the release point back to the buffer length of the variable-length buffer 124. The mute processing can be performed arbitrarily, such as by overwriting the audio signal data with data of volume 0, or by setting header data to ignore subsequent data.

[0040] 3 is a functional block diagram for explaining the audio signal transmission method of the radio device 1 configured as described above. When it is determined which of the microphones 20, 22, and 31 and which of the PTT switches 15 (16), 23, and 32 will be used for transmission, the microphone type detector 43 detects (determines) whether or not there is structural sound leakage between the microphones and the PTT switches, and the delay amount determination processing unit 44 refers to a table based on the detection (determination) result and the delay amount in the AF processor 131, and determines and presets an appropriate buffer length for the variable length buffer 124, which is a storage means.

[0041] Then, when the PTT switches 15 (16), 23, 32 are pressed down and the PTT detector 41 detects that the PTT line has become "connected," the audio signals from the microphones 20, 22, 31 are converted into digital form by the analog / digital converters 122, 162, 172, temporarily stored in the variable-length buffer 124, and then processed by the AF processor 131. After that, the signal passes through the mute circuit 181 (leaving the audio signal as is), becomes a baseband signal of a predetermined modulation method by the baseband processor 141, and is modulated by the frequency modulator 152 before being transmitted.

[0042] On the other hand, when the PTT detector 41 detects that the PTT line is "off" after the PTT switch 15 (16), 23, or 32 is released, there is a possibility that an operating sound is being generated from the microphone 22 of the external microphone 2. Therefore, the PTT detector 41 causes the mute circuit 181 to perform a mute operation from that point onward, muting the audio signal remaining in the variable-length buffer 124 before transmitting, thereby preventing the operating sound from being emitted as an unpleasant popping sound from the speaker 19 on the receiving side. On the other hand, when the built-in microphone 20 or another microphone 31 is used, even if a mute operation is performed when the PTT line is "off" in the same way, the buffer length of the variable-length buffer 124 is set to a short value, and the amount of data overwritten with silent data is small, minimizing the delay time until the call transmitted from the transmitting radio 1 reaches the receiving radio 1. Furthermore, if the operating noise is not picked up, or if it is picked up, it is small enough that it is not annoying to the receiving side, the capacity of the variable length buffer 124 may be set to zero. In this case, no delay other than the delay that absolutely occurs in the transmission process, such as modulation process, will occur, and there will be no truncation.

[0043] As described above, according to the radio 1 of this embodiment, the microphone type detector 43 detects the structural relationship between the microphones 20, 22, 31 used for transmission and the PTT switches 15 (16), 23, 32, and when the structural relationship is such that the microphone 22 picks up the operating sound of the PTT switch 23, as in the case of the external microphone 2, the delay amount setting processing unit 44 increases the buffer length (increases the capacity) of the variable length buffer 124, and when there is no possibility of picking up the operating sound, it shortens the buffer length (decreases the capacity).

[0044] Therefore, when the PTT switches 15 (16), 23, 32 are released, the mute circuit 181 mutes the audio signal in the variable-length buffer 124 based on the release timing of the PTT switches 15 (16), 23, 32. This ensures that even if the microphone 22 picks up the operating sound of the PTT switch 23, as in the case of the external microphone 2, the operating sound is muted and not transmitted, preventing popping sounds from occurring on the receiving side. On the other hand, when there is no possibility that the microphones 20, 31 will pick up the operating sound of the PTT switches 15 (16), 32, as in the case of the PTT switches 15 (16), 32, the amount of muting is minimized, thereby reducing the possibility of the talk (transmission) being cut off.

[0045] The present invention is applicable to communication devices that enable transmission by pressing a PTT switch, such as intercoms and videoconferencing systems. However, in the case of such intercoms and videoconferencing systems, the microphone is often built into the main body and is mounted in the same housing as the PTT switch. However, since the housing is relatively large, it is easy to take measures against the operating noise structurally. Furthermore, in the case of portable radios 1, although the housing is small, it is still possible to some extent to structurally accommodate the built-in microphone 20 and the PTT switch 15 (16).

[0046] However, in the case of the radio 1, as described above, if the microphone 22 is an external microphone 2 equipped with a PTT switch 23, the microphone 22 and the PTT switch 23 are close to each other, making it structurally difficult to take measures against the operating noise. In such a case, by relatively increasing the buffer length of the variable-length buffer 124 and relatively increasing the amount of audio signal muted when the PTT switch 23 is released, it is possible to take an effective measure against the popping noise in the case of a small external microphone 2 equipped with a PTT switch 23 for which it is structurally difficult to take measures against the operating noise.

[0047] Here, the transmission path for the audio signal can be wired or wireless, and can be analog or digital. However, in the case of an analog FM radio line, the S / N ratio is about 40 to 50 dB, and when there is no sound, a hissing noise remains. When the PTT switches 20, 23, and 32 are released to end the call, the transmission signal stops, which stops the operation of the low-frequency amplifier 115 of the receiving circuit and stops the residual noise, allowing the call to be recognized. Therefore, in the case of this analog FM radio line, there is no need to recognize the call ending by the popping sound, and eliminating the unpleasant popping sound is particularly effective. [Explanation of symbols]

[0048] 1 radio 10. Cabinet 12 Power / Volume Knob 13 Channel selector knob 14 Antenna 15 PTT switch 16 Side Switch 17 Display section 18 Operation keys 19 Speaker 20 microphones 2 external microphones 21 Speaker 22 microphones 23 PTT switch 24 Curl cord 25 connectors 27 Microphone type setting section 28 Case 31 Microphone 32 PTT switch 4. Control section 41 PTT detector 42 Mode setter 43 Microphone Type Detector 44 Delay amount determination table 101 Transmit / Receive Switch 112,113 Switch 1111~111 n Demodulator 116 Selector 123 Selector 124 variable length buffer 132,133 Switch 1311~131 n AF processor 1411~141 n Baseband Processor 1811~181 n Mute Circuit

Claims

1. In communications equipment that enables transmission by pressing a press-to-talk switch, a detecting means for detecting a structural relationship between the microphone used for said transmission and said press-to-talk switch; a variable-capacity storage means for temporarily storing the audio signal collected by the microphone; a transmitting means for modulating the audio signal temporarily stored in the storage means in a predetermined modulation mode and transmitting the modulated audio signal; control means for detecting the depression or release of the press-to-talk switch; the control means sets the capacity of the storage means based on the detection result of the detection means, and upon detecting the release of the press-to-talk switch, notifies the transmission means of this, and the transmission means mutes the audio signal temporarily stored in the storage means at the time the press-to-talk switch is released.

2. 2. The communication device according to claim 1, wherein the communication device is a radio, and when the detection means determines that the microphone is an external microphone having the press-to-talk switch, the control means relatively increases the capacity of the storage means, and when the detection means determines that the microphone is not equipped with the press-to-talk switch or is a built-in microphone, the control means relatively decreases the capacity of the storage means.

3. 3. The communication device according to claim 2, wherein the communication device is a radio, the transmitting means has a plurality of modulation modes, and when the detecting means determines that the microphone is an external microphone equipped with the press-to-talk switch, the control means further changes the capacity of the storage means in accordance with the modulation mode.

4. 4. The communication device of claim 3, wherein the plurality of modulation modes includes analog FM modulation.

5. A method for transmitting a voice signal from a communication device that can transmit by pressing a press-to-talk switch, comprising: detecting a structural relationship between the microphone used for transmitting and the press-to-talk switch; a step of presetting a capacity of a variable capacity storage means based on the detection result of the detection; a step of temporarily storing the audio signal collected by the microphone in the storage means; a step of modulating the voice signal temporarily stored in the storage means in a predetermined modulation mode and transmitting the modulated voice signal; and in response to the release of the press-to-talk switch, muting the audio signal temporarily stored in the storage means and transmitting the muted audio signal.

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