JP7747952B2 - Communication device and audio signal transmission method - Google Patents

Description

The present invention relates to an audio signal transmission method and device that prevents the operating sound that may be generated when a press-to-talk switch is released from a communication device that enables transmission by pressing the press-to-talk switch from being reproduced as a pop sound on the receiving side.

In communications devices used in walkie-talkies, intercoms, videoconferencing systems, and other devices that transmit by pressing a press-to-talk switch (also known as a PTT switch), if the microphone and PTT switch are positioned close together, the microphone can pick up the operating sound of the PTT switch when it is released. When the signal is transmitted and the operating sound is demodulated on the receiving side, a popping sound can be generated from the speaker, causing an unpleasant noise for the receiving party. Specifically, when the sender begins to release the PTT switch to stop transmitting and the switch begins to return, the lever that was pressing the switch slides and the spring inside the switch returns, but the switch contacts have not yet been broken, and the communications device continues transmitting. Therefore, these operating sounds are picked up and transmitted by the microphone. The switch contacts then break, disconnecting the PTT line. The control and audio signal processing circuits detect the PTT break, 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.

In the case of intercoms and video conferencing systems, the microphone is often installed in the same housing as the PTT switch, but the housing is relatively large, so measures to reduce the operating noise are easy to implement structurally, 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 structurally, it is possible to use a relatively expensive PTT switch that is highly reliable and has smooth operation.

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 structurally difficult to block the transmission of operating noise. Furthermore, external microphones are accessory (optional) parts, and therefore must be made of relatively inexpensive parts compared to the PTT switch on the radio itself, which makes the operating noise itself louder.

A typical prior art pop noise reduction device has been proposed by the present applicant in Patent Document 1. In this prior art, a digital radio buffers and transmits a transmission audio signal, and when the PTT switch (transmission/reception switching means) is switched to the deactivated position (transmission stopped), data from the time of the switch up to a predetermined time before is replaced with silent data, preventing the operating noise from being reproduced on the receiving side and causing a pop noise.

Patent No. 5343843

The above-mentioned conventional technology is effective in suppressing popping sounds. 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 sounds, it is necessary to set a long period for buffering the transmitted audio signal, which also increases the transmission delay between transmission and reception. On the other hand, as mentioned above, there are cases where popping sounds do not necessarily need to be taken into consideration, such as when the PTT switch and microphone are far apart.

The object of the present invention is to provide a communication device and an audio signal transmission method that can reduce transmission delays 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.

The communications device of the present invention, which enables transmission by pressing a press-to-talk switch, comprises: a detection means for detecting the structural relationship between the microphone used for transmission and the press-to-talk switch; a variable-capacity storage means for temporarily storing an audio signal picked up by the microphone; a 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 a control means for detecting the pressing 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. The transmission means mutes the audio signal temporarily stored in the storage means when the press-to-talk switch is released.

The present invention also provides a method for transmitting an audio signal for a communication device that enables transmission by pressing a press-to-talk switch, and includes the steps of: detecting the structural relationship between the microphone used for transmission and the press-to-talk switch; presetting the capacity of a variable capacitance storage means based on the detection results; temporarily storing an audio signal collected by the microphone in the storage means; modulating the audio signal temporarily stored in the storage means in a predetermined modulation mode and transmitting it; and muting the audio signal temporarily stored in the storage means and transmitting it in response to the release of the press-to-talk switch.

With the above configuration, in communications devices that enable transmission by pressing a press-to-talk switch, such as walkie-talkies, intercoms, and video conference systems, 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 device demodulates this sound, a popping noise is 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.

Specifically, the audio signal collected by the microphone is temporarily stored in a variable-capacity storage means, and then modulated in a predetermined modulation mode and transmitted from the transmission means. When the control means detects the pressing or release of the press-to-talk switch, it causes the transmission means to transmit or stop transmission (switch to reception). Furthermore, the control means 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, and the transmission means, upon receiving the notification, performs the muting process on the audio signal read from the storage means.

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 can be increased and muting can be performed for the period during which the operating sound is generated, based on the timing of the release of the press-to-talk switch, to prevent the transmission of the unpleasant operating sound. If there is no possibility of picking up the operating sound, the capacity of the variable capacitance storage means can be minimized, reducing the possibility of the talk (transmission) being cut off.

Furthermore, the communications device of the present invention is a radio, and 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 an internal microphone, the control means relatively decreases the capacity of the storage means.

In the case of intercoms or video conference systems, the microphone is often mounted on the main unit and in the same housing as the press-to-talk switch. This relatively large housing makes it easy to take structural measures to reduce 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 difficult to take structural measures to reduce 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 that is muted when the press-to-talk switch is released.

This allows for effective noise reduction measures to be taken in the case of small external microphones equipped with press-to-talk switches, which are structurally difficult to address due to their operating noise.

The communications device of the present invention is a radio, wherein the transmitting means has multiple 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 storage means in accordance with the modulation mode.

With 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.

As mentioned above, the transmission path for audio signals can be wired or wireless, and can be analog or digital. However, particularly in the case of analog FM radio modulation, the S/N ratio is around 40-50 dB, and when there is no sound, a hissing residual noise is present. 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, allowing the call to be recognized as ended. Therefore, there is no need to recognize the call as ended by the popping sound, and 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.

As described above, in a communications device that enables transmission by pressing a press-to-talk switch, if the microphone used for transmission is structurally in a position where it picks up the operating sound of the press-to-talk switch, the communications device and audio signal transmission method of the present invention temporarily stores the audio signal picked up by the microphone and performs muting processing for the period during which the operating sound is generated, based on the timing of the release of the press-to-talk switch.

Therefore, if the structure is such that the microphone picks up the operating sound of the press-to-talk switch when it is released, that operating sound can be muted to prevent the annoying popping sound from being heard 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.

1 is a perspective view of a radio that is a communication device according to an embodiment of the present invention; FIG. 2 is a block diagram showing the electrical configuration of the radio and the external microphone. 1 is a functional block diagram for explaining an audio signal transmission method according to an embodiment of the present invention;

Figure 1 is a perspective view of a radio 1, a communications device according to one 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 the connector cover on the right side 1001 of the housing 10. The top 1002 of the housing 10 is provided with a power/volume knob 12, a channel selector knob 13, and an antenna 14. The left side 1003 of the housing 10 is provided with a PTT switch 15 and two side switches 16. The front 1004 of the housing 10 is provided with a display 17 and various operation keys 18, as well as a speaker 19 and a microphone 20. The display 17 displays the transmission and reception frequencies and signal levels. The back of the housing 10 is provided with a battery pack and a clip for attaching to the user's waist belt, etc. The side switch 16 can also be used as a PTT switch for a sub-channel.

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, and one end of the connector 25 is hooked onto the exposed connector, and the other end of the connector 25 is screwed in to connect the terminals.

Figure 2 is a block diagram showing the electrical configuration of radio 1 and external microphone 2. Figure 2 shows only the wireless communication section, and omits parts unrelated to the present invention, such as displays. This radio 1 uses the 150 MHz band and is a dual-mode radio that supports a digital mode that uses 4-level FSK modulation to achieve clear sound quality, and an analog mode that uses FM modulation to easily achieve compatibility with conventional devices. Note that 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, it does not necessarily have to be a dual mode of digital and analog modes, and it does not have to support multiple modulation methods.

A signal received by antenna 14 is input from transmit/receive switch 101 to high-frequency signal amplifier 102, where it is amplified, and then mixed with a local oscillation signal from high-frequency signal generator 104 in frequency converter 103 to be converted into an intermediate frequency signal. Subsequently, the signal is converted into a digital signal by analog/digital converter 105, and demodulated by one of demodulators _111-111n (hereinafter, collectively referred to as 111) selected by input/output switchers 112 and _113. Demodulator 111 corresponds to a modulation mode, such as the digital mode or analog mode, and one of the modes is selected by switchers 112 and 113 in accordance with a setting from mode setter 42 of control unit 4, which will be described later, to decode the audio signal. The decoded audio signal is converted into an analog audio signal by digital/analog converter 114, amplified by low-frequency amplifier 115, and then emitted from speaker 19.

Meanwhile, an audio signal collected by microphone 20 is amplified by low-frequency amplifier 121, converted to a digital signal by analog-to-digital converter 122, and subjected to upsampling, filtering, and other processing by one of AF (Audio Frequency) processors 131 ₁ to 131 _n (hereinafter collectively referred to as 131) selected by input/output switchers 132 and 133. Further, one of baseband processors 141 ₁ to 141 _n (hereinafter collectively referred to as 141) processes the baseband signal according to the selected modulation mode. The processed baseband signal is converted to an analog signal by digital-to-analog converter 151, and a frequency modulator 152 frequency-modulates the local oscillation signal from the high-frequency signal generator 104 to generate a transmission signal. The signal is then amplified by power amplifier 154 and transmitted from antenna 14 via transmission/reception switcher 101. The components downstream of switcher 132 constitute a transmission means.

The switches 112 and 113, demodulator 111, as well as the switches 132 and 133, AF processor 131, and baseband processor 141 are configured in a modulation/demodulation circuit consisting of a DSP, FPGA, or the like. The frequency modulator 152 changes 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.

An external microphone 2 can be connected to the radio 1 of this embodiment via connector 25. It is also possible to use a headset equipped with a microphone 31 for wireless communication, etc. 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 selector 123 and connected to switch 132.

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 can also be used for the PTT switch 15 (16), and both are input to the PTT detector 41 in the control unit 4.

The control unit 4 controls the operation of the radio 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-value FSK modulation or FM modulation) and channel setting set by operating the operation keys 18 (see Figure 1).

It is worth noting that in the radio 1 of this embodiment, the control unit 4 is provided with a microphone type detector 43 that detects the settings of the microphone type setting unit 27 provided on the external microphone 2 side. The microphone type detector 43 and microphone type setting unit 27 constitute a detection means and work together to detect the structural relationship between the microphone 22 and PTT switch 23 of the external microphone 2. Specifically, they determine 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 curl cord 24 and a dedicated terminal may be provided on the connector 25, or the terminals of the PTT switch 23 and microphone 22 may be open (high impedance), pulled up to a predetermined voltage, or preset via the operation key 18.

The microphone type detector 43 detects (determines) whether the external microphone 2 is a standalone microphone or whether it has a PTT switch 23, and if it does have a PTT switch 23, whether it is located midway along the curled cord 24 and does not pick up the operating sound of the PTT switch 23, or whether the PTT switch 23 and microphone 22 are located in the housing 28 and structurally pick up the operating sound of the PTT switch 23. The PTT detector 41 determines whether the built-in microphone 20, external microphone 22, or extension microphone 31 for wireless communication is being used in response to the operation of the corresponding PTT switch 15 (16), 23, or 32.

It is also worth noting that in the radio 1 of this embodiment, a variable-length buffer 124, which is a variable-capacity storage means, is interposed between the selector 123, which serves as the output stage for the audio signal collected by any of the microphones 20, ₂₂ , and ₃₁ , and the switch 132, which serves as the input stage for the transmitting means, and mute circuits _181-181n (hereinafter collectively referred to as ₁₈₁ ) are provided between the AF processors _131-131n and the baseband processors _141-141n . The variable-length buffer 124 can be set to a variable length, and temporarily stores, delays, and outputs the audio signal for a time corresponding to the set buffer length. The control unit 4, which serves as control means, is provided with a delay amount determination table 44 that sets the buffer length, i.e., the delay time.

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 extension microphone 31 is being 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.

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 settings of the mode setting unit 42. That is, if the external microphone 2 is only a standalone microphone, the buffer length is minimized. On the other hand, if the external microphone 2 is equipped with a PTT switch 23, and the PTT switch 23 and microphone 22 are integrally formed in 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. Furthermore, if the external microphone 2 is equipped with a PTT switch 23, but is located midway along 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 integrated into the housing 28 but are structurally unable to pick up the operating sound of the PTT switch 23, the delay amount determination table 44 will set the buffer length to the minimum or a specified non-minimum buffer length.

The delay amount determination table 44 may determine the buffer length according to the structural relationship between the PTT switch 23 and the microphone 22, as described above, depending on the settings of the mode setting unit 42. 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 mechanical structure, and the buffer length can be determined based on this time difference.

In addition, the delay determination table 44 further adjusts the buffer length, i.e., delay time, depending on the settings of the mode setting unit 42, taking into account the processing delay and additional functions of the downstream AF processor 131. Specifically, this adjustment depends on the difference between the analog and digital modes mentioned above, the presence or absence of a noise canceller or equalizer, and other factors. As mentioned above, the radio 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 does not transmit operating noise and minimizes the delay time 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.

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 process can be performed in any way, such as overwriting the audio signal data with data at volume 0, or setting the header data to ignore subsequent data.

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

Then, when the PTT switch 15 (16), 23, 32 is pressed and the PTT detector 41 detects that the PTT line is connected, the audio signal from the microphone 20, 22, 31 is converted to digital 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, it passes through the mute circuit 181 (leaving the audio signal as is), and is converted into a baseband signal using a specified modulation method by the baseband processor 141, and is then modulated by the frequency modulator 152 and transmitted.

In contrast, when the PTT detector 41 detects that the PTT switch 15 (16), 23, or 32 is released and the PTT line is "off," there is a possibility that operating noise is being generated by 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 transmission, thereby preventing the operating noise from being emitted as an unpleasant popping sound from the receiving speaker 19. 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," 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 by the transmitting radio 1 reaches the receiving radio 1. Additionally, 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 can be set to zero. In this case, no delays other than those that absolutely occur in the transmission process, such as modulation processing, will occur, and there will be no cut-off.

As described above, in 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. If 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 if there is no possibility of picking up the operating sound, it shortens the buffer length (decreases the capacity).

Therefore, when the PTT switches 15 (16), 23, and 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, and 32. This ensures that even if the microphone 22 picks up the operating sound of the PTT switch 23, as with the external microphone 2, the operating sound is muted and not transmitted, preventing popping sounds on the receiving side. On the other hand, when there is no possibility that the microphones 20 and 31 will pick up the operating sound of the PTT switches 15 (16), 32, as with the PTT switches 15 (16), 32, the amount of muting is minimized, reducing the possibility of the talk (transmission) being cut off.

The present invention is applicable to communications devices in which transmission is enabled by pressing a PTT switch, such as intercoms and video conferencing systems. However, in the case of these intercoms and video conferencing systems, the microphone is often built into the main body and mounted in the same housing as the PTT switch. This is a relatively large housing, and structurally it is easy to take measures to reduce the operating noise. Furthermore, in the case of portable radios 1, although the housing is small, it is still possible to some extent to make structural adjustments between the built-in microphone 20 and the PTT switch 15 (16).

However, in the case of a radio 1, if the microphone 22 is an external microphone 2 equipped with a PTT switch 23 as described above, the microphone 22 and PTT switch 23 are close to each other, making it structurally difficult to take measures to prevent the operating noise. In such cases, 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 effective measures to prevent popping noise in the case of a small external microphone 2 equipped with a PTT switch 23 that is structurally difficult to prevent the operating noise.

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

1 Radio 10 Housing 12 Power/Volume Knob 13 Channel Switch Knob 14 Antenna 15 PTT Switch 16 Side Switch 17 Display Unit 18 Operation Keys 19 Speaker 20 Microphone 2 External Microphone 21 Speaker 22 Microphone 23 PTT Switch 24 Curl Cord 25 Connector 27 Microphone Type Setting Unit 28 Housing 31 Microphone 32 PTT Switch 4 Control Unit 41 PTT Detector 42 Mode Setter 43 Microphone Type Detector 44 Delay Amount Determination Table 101 Transmission/Reception Switcher 112, 113 Switcher 111 ₁ to 111 _n Demodulator 116 Selector 123 Selector 124 Variable Length Buffer 132, 133 Switcher 131 ₁ to 131 _n AF Processor 141 ₁ to 141 _n Baseband Processor 181 ₁ ~181 _n mute circuit

Claims (5)

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. The communication device according to claim 1, characterized in that if 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 if the detection means determines that the microphone is not equipped with the press-to-talk switch or is an internal microphone, the control means relatively decreases the capacity of the storage means. The communication device according to claim 2, characterized in that it is a radio, the transmitting means has multiple 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 according to the modulation mode. 4. The communication device of claim 3, wherein the plurality of modulation modes includes analog FM modulation. 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 voice signal temporarily stored in the storage means and transmitting the muted voice signal.