Apparatus for automatically muting the output of a recording device during recording

An apparatus for preventing a digital audio tape recorder from transmitting signals to an external device during recording by selectively interrupting the output signal from the digital audio tape recorder by a control device which produces a muting signal when a record signal and a muting detection signal are present at the same time.

BACKGROUND OF THE INVENTION 
This invention relates to a signal recording apparatus, and more 
particularly is suitable to be adapted to, for example, a compact rotary 
head type digital audio tape recorder. 
In a conventional rotary head type digital audio tape recorder (DAT) of 
this kind, a line input terminal 2 for inputting an audio signal from an 
external device to a DAT 1 is provided and a line output terminal 3 from 
which an audio signal is outputted to the external device is provided, as 
shown in FIG. 1. 
Therefore, by connecting a line output terminal 6 of, for example, a 
cassette tape recorder with radio receiver 5 and the line input terminal 2 
of the DAT 1 through a line cord 8 and connecting a line input terminal 7 
of the cassette tape recorder with radio receiver 5 and the line output 
terminal 3 of the DAT 1 through a line cord 9, it is possible to send 
radio broadcasting received by the cassette tape recorder with radio 
receiver 5 to the DAT 1 through the line cord 8 for recording it in the 
DAT 1 or to output a reproduced sound from the DAT 1 from a speaker of the 
cassette tape recorder with radio receiver 5 through the line cord 9 by 
making the DAT 1 in a reproduction mode and outputting an audio signal on 
the line output terminal 3. 
A recording and/or reproducing apparatus such as the DAT 1 and the cassette 
tape recorder with radio receiver 5 has, in general, a construction in 
which, when it is controlled to a line input mode, the audio signals 
inputted from the line input terminals 2 and 7 are outputted from the line 
output terminals 3 and 6, respectively, as they are, so that the audio 
signals outputted from the line output terminals 3 and 6 can be monitored 
by user. 
Accordingly, when the DAT 1 is made to a line input recording mode while 
the cassette tape recorder with radio receiver 5 being controlled to a 
line input mode so as to monitor the recording sound of the DAT 1 by means 
of the speaker of the cassette tape recorder with radio receiver 5, an 
audio signal inputted from the Line input terminal 2 of the DAT 1 is 
gradually amplified by a loop formed by the line output terminal 3 of the 
DAT 1, the line cord 9, the line input terminal 7 of the cassette tape 
recorder with radio receiver 5, the line output terminal 6, the line cord 
8 and the line input 2 of the DAT 1, causing an oscillation phenomenon to 
occur and so there was a problem that rasping oscillation sound is 
produced from the speaker of the cassette tape recorder with radio 
receiver 5. 
As one method for solving this problem, it may be considered to disconnect 
the line cord 9 when the DAT 1 is made to the line input recording mode or 
other methods such as switching the line input mode of the cassette tape 
recorder with radio receiver 5 to another mode, etc., may be considered, 
however, when such method is employed, there is a problem that it is 
impossible to avoid user's troublesome handling and, so, it was not yet 
enough as solution. 
SUMMARY OF THE INVENTION 
In view of the foregoing, an object of this invention is to provide a 
signal recording apparatus capable of more easily and reliably preventing 
oscillation phenomenon. 
The foregoing object and other objects of the invention have been achieved 
by the provision of a signal recording apparatus having output means 16 
for outputting an output signal S6 to an external device 5, when it is 
controlled to a recording state, the output signal S6 outputted from the 
output means 16 is controlled to an output stop state. 
By not outputting the output signal S6 from the output means 16 when the 
recording apparatus 10 is controlled to the recording state, it is 
possible to not form such loop as producing the oscillation phenomenon 
between the said recording apparatus 10 and the external device 5, to 
thereby not produce rasping sound due to oscillation phenomenon. 
The nature, principle and utility of the invention will become more 
apparent from the following detailed description when read in conjunction 
with the accompanying drawings in which like parts are designated by like 
reference numerals or characters.

BRIEF DESCRIPTION OF THE INVENTION 
Preferred embodiments of this invention will be described with reference to 
the accompanying drawings. 
FIG. 2 shows a DAT 10 as a whole. By operating a reproduction switch 13A, a 
recording switch 13B, a fast feed switch 13C or a rewind switch 13D of an 
operation switch set 13 provided in a body 12 of the DAT 10, the DAT 10 is 
set to a reproduction mode, a recording mode, a fast feed mode or a rewind 
mode, respectively. According to the setting mode, an audio signal is 
reproduced from or recorded on a magnetic tape of a tape cassette loaded 
in a tape cassette loading portion 
Further, a line input and output adapter 16 is connected to the body 12 of 
the DAT 10, and, if the reproduction switch 13A or the recording switch 
13B of the body 12 of the DAT 10 is switched on when the line input and 
output adapter 16 is connected, the body 12 of the DAT 10 is controlled to 
a line output reproduction mode or a line input recording mode, 
The line input and output adapter 16 is further provided with a power 
source input circuit for receiving an external power source, so that, 
while the line input and output adapter 16 connected to the body 12 of the 
DAT 10, the external power source can be supplied to the body 12 of the 
DAT 10 through a power source cord 17. 
The line input and output adapter 16 is further provided with a muting 
switch 21, and it is made to not output an output signal through the line 
output terminal 19 in the recording mode by on-operating the said muting 
switch 21. 
As shown in FIG. 3, in the DAT 10, the operation switch set 13 of the body 
12 of the DAT 10 is connected to an input control circuit 23, and a 
control signal S1 corresponding to a key switch operated by the user is 
sent to a system control circuit 24 of a micro computer construction. 
When the reproduction switch 13A is switched on the system control circuit 
24 sends a control signal S8 for controlling to the reproduction mode to 
signal processing circuit 25 to output a reproduced signal from the 
magnetic tape through a connecting terminal 32 of the body 12 of the DAT 
and through a connecting terminal 42, a resistor R2 and the line output 
terminal 19 of the line input and output adapter 16 as an output audio 
signal S6. 
On the other hand, when the recording switch is switched on, the system 
control circuit 24 takes an input audio signal S5 inputted through the 
line input terminal 18 of the line input and output adapter 16 which is 
supplied to the signal processing circuit 25 through a resistor R1 and 
connecting terminals 41, 31, and records this signal after conversion into 
a recording signal. 
Further, a power source input (+B) inputted through the line input and 
output adapter 16 is supplied to the signal processing circuit 25 through 
connecting terminals 43 and 33. 
Here, to the system control circuit 24, a power source VCC is connected to 
a detection input end for detecting a state of the muting switch 21 of the 
line input and output adapter 16. While the muting switch 21 is in an off 
state, a detection signal S2 inputted to the said detection input end 
rises to "H" level and, when the muting switch 21 is in an on state, the 
detection signal S2 goes down to "L" level. 
Further, the system control circuit 24 is made such that a muting control 
signal S3 goes down to "L" level only when the muting switch 21 is 
switched on causing the detection signal S2 to be at the "L" level and the 
recording switch 13B is switched on to set the DAT 10 in the recording 
mode. 
The muting control signal S3 is made inputted to base of PNP transistor Q2 
through connecting terminals 35 and 45 and the transistor Q2 switches on 
when the muting signal S3 goes down to the "L" level and thereby supplies 
the power source input (+B) to a base of a NPN transistor Q1 through a 
resistor R3 to thereby operate the transistor Q1 on. 
Accordingly, the output audio signal S6 outputted through the connecting 
terminals 32 and 42 from the signal processing circuit 25 of the body 12 
of the DAT 10 flows through the resistor R2 and the transistor Q1 to 
ground, so that the audio signal S6 is controlled such that it is not 
outputted from the line output terminal 19. 
By controlling the output audio signal S6 by using the multi-stage 
transistors Q1 and Q2 at this point, it is made that there is no 
distortion of the output audio signal S6 produced. 
In the construction mentioned above, where the line output terminal 6 of 
the cassette tape recorder with radio receiver 5 is connected to the line 
input terminal 18 of the line input and output adapter 16 through the line 
cord 8 and the line input terminal of the cassette tape recorder with 
radio receiver 5 is connected to the line output terminal 19 of the line 
input and output adapter 16 through the line cord 9, as shown in FIG. 4, 
when the muting switch 21 of the line input and output adapter 16 is 
switched on to record, in the DAT 10, radio broadcasting received in the 
cassette tape recorder with radio receiver 5 is supplied to the DAT 10 
through the line cord 8, it is possible to control the DAT 10 such that 
the input audio signal S5 inputted from the line input terminal 18 is not 
outputted from the line output terminal 19 even if the signal is outputted 
to the side of the line input and output adapter 16 through the signal 
processing circuit 25 as the output audio signal S6, since the muting 
switch 21 is switched on and the recording switch 13B of the DAT 10 is 
simultaneously switched on. 
Accordingly, since, even if the cassette tape recorder with radio receiver 
5 is in the line input mode state, there is no loop including the output 
terminal 19 of the DAT 10, the line cord 9, the line input terminal 7 of 
the cassette tape recorder with radio receiver 5, the line output terminal 
6, the line cord 8 and the line input terminal 18 of the DAT 10 formed, 
such generation of oscillation phenomenon as in the conventional device 
can be avoided. 
On the other hand, in the reproduction mode, it is possible to output the 
reproduced output audio signal S6 by setting the muting control signal S3 
to the system control circuit 24 (FIG. 3) to the "H" Level even if the 
muting switch 21 is switched on. 
When an audio device constructed such that, in the line input mode, an 
audio signal inputted from the line input terminal is not outputted 
through the line output terminal as it is, is connected instead of the 
cassette tape recorder with radio receiver 5, it is enough to switch off 
the muting switch 21 of the line input and output adapter 16, in which 
case, it is possible to monitor a state of sound recorded in the DAT 10 by 
means of a speaker on the side of the audio device. 
According to the above mentioned construction, it is possible to control 
the output audio signal S6 such that it is not outputted from the line 
output terminal 19 only when the recording mode is detected, by switching 
on the muting switch 21, by which it is possible to avoid generation of 
oscillation phenomenon between the DAT 10 and an external device (the 
cassette tape recorder with radio receiver 5 in this embodiment) and to 
not generate rasping sound from the speaker of the external device without 
requiring user's troublesome operations such as switching operations of 
mode switching switches of the external device. 
Although, in the above described embodiment, the case where the audio 
signal from the external device is recorded has been described, the 
present invention is not limited thereto and can be applied widely to a 
recording of audio signal inputted by various input means such as a 
recording of a signal from an external microphone, etc. 
Further, although, in the embodiment mentioned above, the present invention 
has been described as applied to the digital audio tape recorder, the 
present invention is not limited thereto and is applicable to various 
other audio tape recorders. 
In addition, although, in the embodiment mentioned above, the present 
invention has been described as applied to the recording and reproducing 
apparatus for recording an audio signal, the present invention is not 
limited thereto and is applicable widely to various other recoding 
apparatus for recording other signals. 
As described, since, according to the present invention the output means 
does not provide any output signal when controlled during the recording 
state, it is possible to realize a recording apparatus capable of doing 
not generate oscillation phenomenon between an external device. 
While there has been described in connection with the preferred embodiments 
of the invention, it will be obvious to those skilled in the art that 
various changes and modifications may be made therein without departing 
from the invention, and it is aimed, therefore, to cover in the appended 
claims all such changes and modifications as fall within the true spirit 
and scope of the invention.