JPH0629761Y2 - Test tune generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a test tone generator used for frequency characteristic check and bias adjustment of a tape deck.

[Prior Art] In a conventional test tone generator, as shown in FIG.
The sine waves from the high-frequency oscillator 10 and the low-frequency oscillator 12 are switched by the changeover switch 14 so that the attenuator 16
The attenuation rate of the attenuator 16 is switched by the changeover switch 18. The changeover switches 14 and 18 are changed over by a control signal from the microcomputer 20.

The test tone signal output from the attenuator 16 is
It is supplied to a two-head tape deck and recorded on a magnetic tape, the magnetic tape is rewound, and then a test tone is reproduced. The frequency characteristic of the tape deck is checked by the level of this test tone.

Here, since the level of the test tone is generally low, the attenuation rate of the attenuator 16 is made small only at the beginning of recording so that the magnetic head can be automatically cued when the magnetic tape is rewound after the end of recording.

Since the high-frequency oscillator 10 and the low-frequency oscillator 12 are relatively expensive, in another conventional example, as shown in FIG. 4, square waves are output from the output terminals a and b of the microcomputer 20, respectively, and the square waves are low-passed. The sine wave is supplied to the filters 22 and 24 and converted into a sine wave, and the changeover switch 14 is switched to supply the sine wave from the low-pass filter 22 or the low-pass filter 24 to the attenuator 16. The changeover signal of the changeover switch 18 and the changeover signal of the changeover switch 14 for changing the attenuation rate of the attenuator 16 are supplied from the output terminals c and d of the microcomputer 20, respectively.

The low-pass filters 22 and 24 are cheaper than the high-frequency oscillator 10 and the low-frequency oscillator 12 shown in FIG. 3, and can be constructed at a lower cost than the test tone generator shown in FIG.

[Problems to be Solved by the Invention] However, in the test tone generator shown in FIG. 4, the number of output points of the microcomputer 20 is two more than the number of output points of the microcomputer 20 shown in FIG. For this reason, when the number of output points of the signal used for other processing is large and the number of output points is insufficient, it is necessary to provide a new output port (LSI), and the circuit becomes complicated accordingly. , Will be expensive.

In view of the above problems, it is an object of the present invention to provide a test tone generator having a simple structure and a low cost.

[Means for Solving the Problems] In the test tone generator according to the present invention, a square wave oscillating means for outputting a plurality of square waves of different frequencies, and an output from the square wave oscillating means in response to a switching command. Characterized in that it has a low-pass filter for changing the pass band of a square wave to be output and outputting a square wave or a sine wave, and a control means for outputting the switching command to the square-wave oscillating means and the low-pass filter. In addition, the low-pass filter first sets the pass band of the square wave output from the square wave oscillating means to be wide, sets the pass band of the square wave to be output next to be narrow, and then outputs the square wave. It is characterized by narrowly setting the passbands of square waves of different frequencies.

[Operation] The tape deck is set to the recording state, and first, the pass band of the low-pass filter is widened to allow the square wave to pass, and this is recorded on the magnetic tape. Next, the pass band of the low-pass filter is narrowed to convert the square wave into a sine wave, which is recorded on the magnetic tape. Next, square waves with different frequencies are converted into sine waves by a low-pass filter and recorded on a magnetic tape.
If necessary, sine waves of different frequencies are recorded on the magnetic tape in the same manner as above.

Next, the magnetic tape is rewound by a tape deck equipped with a heading function. Since the signal level of the square wave is higher than the signal level of the sine wave, it is possible to find the test tone without reducing the attenuation rate of the attenuator.

[Embodiment] A preferred embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a block circuit of the test tone generator, which includes output terminals a and b of the microcomputer 20.
The input terminal of the low-pass filter 26 and the control terminal of the changeover switch 28 are connected to each other. From this output terminal a, a square wave of low frequency f1 and a square wave of high frequency f2 are sequentially output. The low-pass filter 26 is the output terminal b of the microcomputer 20.
The changeover switch 28 is operated by the changeover commands S1 and S2 supplied from the switch, so that the pass band is changed over. The low-pass filter 26 is followed by the attenuator 16, and the level of the signal output from the low-pass filter 26 is lowered so that the test tone signal is output from the attenuator 16.

In the pass band of the low-pass filter 26, the square wave of the low frequency f1 is converted into a sine wave in response to the switching command S1, and the square wave of the low frequency f1 passes through in response to the switching command S2, and the square wave of the high frequency f2 is passed. The width is such that the wave is converted to a sine wave. Hereinafter, these passbands are referred to as a passband for the low frequency f1 and a passband for the high frequency f2.

Next, the software configuration of the microcomputer 20 will be described with reference to FIG.

Here, it is assumed that the output terminal of the attenuator 16 is connected to the recording input terminal of the tape deck and the tape deck is in the recording state.

In step 100, the switching command S2 is output from the output terminal b of the microcomputer 20 to set the pass band of the low pass filter 26 for the high frequency f2. Next, step 102.
X is set to f1, and the process proceeds to step 104 and FIG. 2 (B).
Execute the subroutine shown in.

That is, the period T ₀ of the high level (H) and the low level (L) of the square wave is A / X. Further, the wave number N ₀ of the square wave to be output is BX. Here, A and B are constants.

Next, in step 202, the timer T is cleared, and in step 204, the output terminal a of the microcomputer 20 is set to H. The output value of the microcomputer 20 is latched here. Next, the processes of steps 206 and 208 are repeated until the value of the timer T reaches the value of T ₀ set in step 200, and the timer T is incremented. As a result, the output terminal a of the microcomputer 20 becomes H for the set time T ₀ . Next, in step 210, the timer T is cleared, and in step 212
Then, the output terminal a of the microcomputer 20 is set to L.
Next, in steps 214 and 216, the process waits until the set time elapses. As a result, the output terminal a of the microcomputer 20 becomes L for the set time T ₀ . Next step 21
Decrement the wave number N at 8. Next, the process returns from step 220 to step 202, and the above processing is repeated. N ₀
When it is repeated, N = 0 in step 220 and the process returns to step 106 of the main routine.

In this way, the square wave of the low frequency f1 is supplied to the low pass filter 26 from the output terminal a of the microcomputer 20.

The pass band of the low pass filter 26 is set for the high frequency f2 in step 100, and the square wave of the low frequency f1 is supplied to the attenuator 16 through the low pass filter 26. Since the signal level of this square wave is relatively higher than that of the sine wave whose waveform is converted by the low-pass filter 26, it is detected when the test tone is recorded on the magnetic tape and then rewound.

Next, in step 106, the pass band of the low-pass filter 26 is switched to the low frequency f1, and in step 108, the same processing as step 104 is performed. As a result, a square wave of low frequency f1 is supplied from the output terminal a of the microcomputer 20 to the low pass filter 26 and converted into a sine wave, and the attenuator 16 outputs a low frequency test tone signal.

Next, in step 110, the pass band of the low-pass filter 26 is switched to the high frequency f2, and in step 112, X is set to f.
2, the subroutine shown in FIG. 2B is executed at step 114. As a result, the microcomputer 2
The square wave of high frequency f2 is supplied from the output terminal a of 0 to the low pass filter 26 and converted into a sine wave, and the attenuator 16 outputs a high frequency test tone signal.

In this embodiment, the number of output points of the microcomputer 20 is two, which is half the number of output points shown in FIG. Further, since the square wave for cueing is first output, it is not necessary to provide the changeover switch 18 as shown in FIGS. 3 and 4, and the structure is simple.

[Effect of the Invention] In the test tone generator according to the present invention, the pass band of the low-pass filter is switched to output a square wave first, and the signal level thereof is higher than the level of the test tone signal. , This square wave can be cueed with a tape deck equipped with a cueing function, so that it is not necessary to switch the attenuation amount of the attenuator, the attenuator configuration is simple, and the changeover switch for switching the attenuator is Further, it is unnecessary, and since it is not necessary to supply a control signal to the changeover switch, the number of output points of the microcomputer can be reduced, and there is an excellent effect that the configuration is simple and the cost is low.

[Brief description of drawings]

1 and 2 relate to an embodiment of the present invention, FIG. 1 is a block circuit diagram showing a hardware configuration, and FIG. 2 is a flowchart showing a software configuration. 3 and 4
The figure is a block circuit diagram of a conventional example. 16 ... Attenuator 20 ... Microcomputer 26 ... Low-pass filter 28 ... Changeover switch

Claims (2)

[Scope of utility model registration request] 1. A square wave oscillating means for outputting a plurality of square waves of different frequencies, and a square wave or a sine wave which changes a pass band of the square wave outputted from the square wave oscillating means in response to a switching command. A test tone generating apparatus comprising: a low-pass filter that outputs a wave; and a control unit that outputs the switching command to the square-wave oscillating unit and the low-pass filter. 2. A low pass filter first sets a wide pass band of a square wave output from the square wave oscillating means, sets a narrow pass band of a square wave output next, and then outputs the square wave. The test tone generator according to claim 1, wherein the pass bands of square waves of different frequencies are set narrow.