JPS6217424B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a so-called hands-free telephone that can make and receive calls without using a handset, using a speaker and a microphone, and without manually switching between transmission and reception. .

Conventional telephones that do not use a hand set include a combination of a receiving device such as earphones or a headphone, which prevents the sound of the incoming call from leaking outside, and a microphone, or a transmitting device, such as a speaker and close-talk microphone, that transmits only the voice of the caller. Although there are telephones that use a combination of devices, these systems have the disadvantage that earphones, a headphone, or a close-talking microphone must be worn on the body when making a call. However, if a normal speaker and microphone are used, although the above-mentioned disadvantages are eliminated, there is a high possibility that echoes and ringing will occur due to the acoustic coupling between the speaker and the microphone, as shown in Figure 1. A transmitting circuit consisting of a microphone 2 and a variable gain amplifier 5 for transmitting, a speaker 1 and a variable gain amplifier 3 for receiving
A circuit 4 is used which controls the gain of the receiving circuit based on the audio signal level, but it has problems such as distortion at the beginning of the speech and malfunction in a high noise environment.

The purpose of the present invention is to improve the quality of the transmitted audio signal without causing echoes or ringing even when the speaker and microphone are acoustically coupled, without cutting off the beginning of the speech or malfunctioning due to noise, and in addition, even when the speaker is connected to the microphone, the quality of the transmitted audio signal can be improved. The object of the present invention is to provide a so-called hands-free telephone that is capable of completely simultaneous transmission and reception.

The hands-free telephone of the present invention has first and second means for dividing the voice spectrum band into narrow bands at equal intervals, sequentially numbering them from the lowest frequency, and transmitting only the even-numbered and odd-numbered narrow band spectra, respectively. providing a received audio signal to a speaker via one of the first and second means, and providing the audio supplied to the microphone to the other of the first and second means, the output signal being It is characterized in that the output signal and the frequency-shifted signal of this output signal are combined and sent as transmission audio.

FIG. 2 is a block diagram of a frequency-divided hands-free telephone associated with the present invention.

FIG. 2 shows a first embodiment of the invention. Further, FIGS. 3a to 3e show the frequency characteristics and signal spectra of each part of FIG. 2.

The explanation will be given below according to the figures.

The received audio signal a from the receiver or 2-wire/4-wire converter 6 has audio spectral bands equally spaced (e.g.
The spectrum is divided into narrow bands at intervals of 100 Hz), and when numbered sequentially from the low frequency, the receiver circuit 7 transmits only the narrow band spectrum of the even numbered points, and the spectrum is transmitted to the third frequency band.
The signal changes from a to b in the diagram and is transmitted from the speaker 1 as received sound. On the other hand, the voice emitted by the caller is converted into an electrical signal c by the microphone 2, and the spectrum is converted into electrical signals c to d in FIG. It is then sent to a transmitter or 2-wire/4-wire converter as a transmitted audio signal d.
On the other hand, the received audio signal sent out as the received sound from the speaker 1 is sent to the microphone 2 as an electrical signal e.
Since the converted signal does not have an odd-numbered narrow band spectrum, it is blocked by the transmitting circuit 8 and is not sent out as a transmitting signal, causing echoes and ringing. It will never occur.

The gain signs of circuits 7 and 8 are shown in FIGS. 4a and 4b, respectively. For a specific example of this circuit, please refer to Komachi et al., "Comb Filter Using Charge Transfer Element," Electroacoustic Research Group Material EA73-25 (1973).

FIG. 5 is a block diagram showing an embodiment of the hands-free telephone according to the present invention. FIGS. 6a to 6d are waveform examples of each part in FIG. 5. When the hands-free telephones shown in Figure 2 are used face-to-face, the signal from each other is not transmitted as an acoustic signal, so this is to prevent this, and when using another hand set, etc. In order to improve the quality of the transmitted audio signal as much as possible, the input signal from the microphone 2 (FIG. 6a) is passed through the transmitting circuit 8 which has frequency characteristics complementary to that of the receiving circuit 7. b) and its frequency shifted upward (or downward) by the frequency shift circuit 9 (FIG. 6 c) are added and synthesized by the addition/synthesis circuit 10, resulting in the result shown in FIG. 6 d. This is to send out a transmission audio signal that does not approximately compensate for the spectrum blocked by the transmission circuit 8.

[Brief explanation of the drawing]

FIG. 1 is an example of a conventional hands-free telephone. FIG. 2 is a block diagram of a hands-free telephone not related to the present invention, and FIGS. 3a to 3e are spectra of each signal in FIG. 2. Figure 4 a and b
are the frequency characteristics of circuits 7 and 8 in FIG.
FIG. 5 is a block diagram showing an embodiment of the hands-free telephone according to the present invention, and FIG. 5 shows the spectrum of each signal shown in FIGS. 6a to 6d. In the figure, 1... speaker, 2... microphone, 3...
... Variable gain amplifier for receiving calls, 4... Variable gain amplifier controller, 5... Variable gain amplifier for sending calls, 6... Transmitter/receiver or 2-wire 4-wire converter, 7... Receiving circuit,
8...Talking circuit, 9...Frequency shift circuit, 10...
...It is an addition synthesis circuit.

Claims (1)

[Claims] 1. In a hands-free telephone that uses a speaker and a microphone to make simultaneous loudspeaker calls, the voice spectrum band is divided into narrow bands at equal intervals, numbers are sequentially assigned starting from the lowest frequency, and only the even-numbered and odd-numbered narrow band spectra are transmitted. first and second means for supplying a received audio signal to the speaker via one of the first and second means, and for transmitting audio supplied to the microphone to the first and second means. A hands-free telephone, characterized in that the output signal and the frequency shift signal of the output signal are combined and sent as a transmitted voice.