JP2948964B2 - Audio signal playback method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing system for obtaining an original audio signal from a magnetic tape on which an analog audio signal is scrambled and recorded.

[0002]

2. Description of the Related Art It is well known that an analog audio signal is recorded on a magnetic tape using a tape recorder.

[0003]

When an analog audio signal is recorded on a magnetic tape as described above, there may be a case where secrecy is desired depending on the recorded content. For example, it is conceivable to scramble an analog audio signal in order to impart secrecy.

When scrambling an analog audio signal, scrambling information is required to reproduce the original analog audio signal. For example, a scrambling information may be provided by providing a header section.

SUMMARY OF THE INVENTION The present invention provides a reproducing method capable of reproducing an original audio signal from a recording medium in which an analog audio signal is scrambled and recorded.

[0006]

According to the present invention, a block comprising a header portion having a key code and a segment portion having an audio signal for a predetermined period scrambled according to the key code is continuously recorded. When an audio signal is reproduced from a recording medium, the original audio signal is obtained by descrambling the audio signal of the segment portion of the reproduction signal with a descrambling pattern corresponding to a key code detected from a header portion of the reproduction signal. is there.

In this case, for example, when the same key code is detected twice or more consecutively from the header of the reproduced signal, the descrambling process is started, and thereafter, the key detected from the header of three consecutive blocks is started. When two or more key codes match, the descrambling process is continued with a descrambling pattern corresponding to the key code.

[0008]

The key code is detected from the header part of each block of the reproduction signal, and the audio signal of the segment part is descrambled by the descrambling pattern according to the key code, so that the original audio signal can be easily reproduced. .

When the same key code is continuously detected two or more times from the header portion of the reproduction signal, the descrambling process is started. Thereafter, two of the key codes detected from the header portions of three consecutive blocks are started. When the above key codes match, the descrambling process is continued with the descrambling pattern according to the key code, so that the key code detected from the reproduced signal due to a physical failure such as a scratch on the magnetic tape may be lost. Even if the error occurs, if the error is not continuous, the descrambling process using the correct key code is started and the descrambling process using the correct key code is continued.

[0010]

An embodiment of the present invention will be described below with reference to the drawings. In this example, an audio signal is scrambled on a magnetic tape and recorded and reproduced.

First, the format of a recording signal will be described with reference to FIGS.

As shown in FIG. 6A, one block of signal is allocated every 600 msec. Each block includes 119.
It is composed of a 5 msec header section and a 480.5 msec segment section (shown in FIG. 6B).

FIG. 7 shows the format of the header section. 12.5K in the first 10msec area of the header
A burst signal of 9 Hz is provided, followed by a silent region of 9 msec, and a 24-bit password code and a 16-bit key code are provided in a subsequent region of 100.5 msec (shown in FIG. 7A).

In the first and last 0.5 msec areas of the 100.5 msec period, 12.5K is used for signal separation.
Hz burst signals are arranged, and bit signals are arranged between these burst signals (shown in FIG. 7B). A region of 2 msec is provided for distributing each bit signal, and a silent region of 0.5 msec is provided between each region.

The bit signal is configured as shown in FIG. 7C. That is, a signal of 8 KHz is inserted into 8 cycles to be a signal of data “0”, while a signal of 8 KHz is inserted into 16 cycles to be a signal of data “1”. FIG. 7C is an example when the password is “011...”.

FIG. 8 shows the format of the segment part. 0.5mse at the beginning and end of the segment
In the area c, a 12.5 KHz burst signal is arranged for signal separation (shown in FIG. 8B), and an audio signal of 600 msec is arranged between these burst signals.

The audio signal for 600 msec is 5
After being divided into 12 periods of 0 msec and rearranged by a scramble pattern corresponding to the key code arranged in the header section, they are sequentially arranged in areas # 1 to # 12 (shown in FIG. 8A).

1 msec is applied to both ends of each of the areas # 1 to # 12.
In addition to the provision of a margin portion of c, a 12.5 KHz burst signal is allocated for signal separation in a region of 0.5 msec between the margin portion of one region and the other region (FIG. 8).
B).

Incidentally, the area of # 1 to # 12 is 37.5.
Since there is only msec and an audio signal of 50 msec cannot be directly allocated, the audio signal is allocated after being subjected to time axis compression processing as follows.

That is, the analog audio signal has 24
At the sampling frequency of KHz, it is converted into a digital signal and written to the memory,
It is read out with a 2 KHz clock. Thus, the audio signal for each 50 msec is 37.5 ms.
ec, and can be arranged in the areas # 1 to # 12 (37.5 msec period).

At the margins of 1 msec provided at both ends of each of the regions # 1 to # 12, the signals at both ends of the audio signal arranged in each region are extended.

The rearrangement process based on the scramble pattern and the formation of the signal arranged in the marginal portion are executed, for example, by controlling the read address of the memory in the above-described time axis compression process.

The rearrangement process and signals recorded in the margin will be further described with reference to FIG.

For example, when the audio signal is divided into 50 msec each as shown in FIG.
As shown in FIG. 9B, the signal arranged at the margin for the audio signal for sec is formed by extending the signal at both ends. And the original audio signal is DATA1,
When the order is DATA2, DATA3, and DATA4 (shown in FIG. 9A), DA is determined by a scramble pattern.
When rearranged in the order of TA3, DATA1, DATA4, and DATA2, a recording signal is formed as shown in FIG. 9C.

FIG. 10 shows the frequency spectrum of the recording signal. As described above, since the audio signal is recorded after the time axis compression processing, when the band of the original audio signal is limited to 9 MHz or less (shown by a broken line), the band of the actually recorded audio signal is limited to 12 MHz or less. (Shown by a solid line). As a result, the audio signal and the 12.5 KHz burst signal are recorded without being mixed, and it is possible to prevent the 12.5 KHz signal from being detected from the audio signal during reproduction and the header part from being erroneously detected.

In this embodiment, a recording signal in the above-described format is recorded on a magnetic tape and reproduced from the recording tape.

FIG. 1 shows an example of a recording and reproducing apparatus for recording and reproducing an audio signal on a magnetic tape in the recording signal format as described above.

In FIG. 2, an analog audio signal SA1 supplied to an audio-in terminal 1 is supplied to a fixed terminal on the a side of the switch circuit 2. The reproduction signal SA2 output to the audio-out terminal 3b of the cassette deck 3 using, for example, a compact audio cassette tape is supplied to the fixed terminal on the b side of the switch circuit 2. The switching of the switch circuit 2 is controlled by the CPU 4 and is connected to the a side during recording and to the b side during reproduction.

The output signal of the switch circuit 2 is supplied to an A / D converter 6 after band-limited by a low-pass filter 5,
For example, it is converted into digital audio data of 16 bits per sample.

Reference numeral 7 denotes a sequence generator, to which a control signal is supplied from the CPU 4 to control its operation. The A / D converter 6 is supplied with the clock CK1 from the sequence generator 7, and performs sampling in synchronization with the clock CK1. The frequency of the clock CK1 is 24 KHz during recording and 32 KHz during reproduction.

The digital audio data output from the A / D converter 6 is transferred to the RAM via the data buffer 8.
9 is supplied as write data. In this case, the sequence generator 7 outputs the RA
An address signal is supplied to M9, and audio data is written to a predetermined address of RAM9.

At the time of recording, the audio data output from the A / D converter 6 is sequentially written into the RAM 9, but at the time of reproduction, the audio signals arranged in the # 1 to # 12 areas of the segment portions of each block are digitally converted. Only audio data is written to the RAM 9.

The reproduced signal SA 2 output to the audio-out terminal 3 b of the cassette deck 3 is supplied to the bit burst detection circuit 11. In the detection circuit 11, 1
When a 2.5 KHz burst signal is detected,
A bit signal (a password code and a key code) is detected based on the number of cycles of the Hz signal, and the detected signal is supplied to the sequence generator 7.

At the time of reproduction, a 12.5 KHz burst signal arranged at the head of the header of each block is detected from the reproduction signal SA2 output to the audio-out terminal 3b of the cassette deck 3 so that the header of each block is detected. Part is detected. In addition, 12.5
When a KHz burst signal is detected, # 1 to # 1 are detected.
Two areas are detected. Based on this, control is performed so that only the audio data obtained by digitally converting the audio signals arranged in the areas # 1 to # 12 are written in the RAM 9 as described above.

The audio data written in the RAM 9 is read out at the time of recording with a clock of 32 KHz and is compressed on the time axis, and is reproduced at the time of 24 KHz.
Reading is performed with a clock of Hz and the time axis is expanded. In this case, at the time of recording, reading is performed at a timing corresponding to the areas # 1 to # 12 (including the marginal portion) of the recording signal format.

At this time, at the time of recording, a scrambling pattern corresponding to the key code generated at random by the CPU 4 and supplied to the sequence generator 7 is used for the recording.
50 msec of each audio signal for 0 msec
The rearrangement of audio data corresponding to the audio signal of 12 / c period, and thus the scrambling process is performed, and the data at both ends of the 50 msec audio data is continuously extended by 1 msec and read, and the data of the marginal portion is read. It is formed.

On the other hand, at the time of reproduction, the reproduction signal SA2
With the descrambling pattern corresponding to the key code detected by the detection circuit 11, the audio data in the areas # 1 to # 12 is rearranged, and thus the descrambling process is performed.

The rearrangement of the audio data and the formation of the data of the marginal portion are performed by controlling the address signal supplied from the sequence generator 7 to the RAM 9.

The audio data read from the RAM 9 is supplied to the D / A converter 12 via the data buffer 8. The clock CK2 is supplied from the sequence generator 7 to the D / A converter 12. The frequency of the clock CK2 is set to 32 KHz during recording, and is set to 24 KHz during reproduction.
Hz.

The analog audio signal output from the D / A converter 12 is supplied to the movable terminal of the switch circuit 14 after being band-limited by the low-pass filter 13. Switching of the switch circuit 14 is controlled by the CPU 4,
Connected to the a side during recording, and connected to the b side during reproduction. The fixed terminal on the b side of the switch circuit 14 is connected to the audio-out terminal 15.

At the time of recording, not described above, the personal identification code supplied to the CPU 4 by the user's operation of the keyboard 17 is supplied to the sequence generator 7 together with the key code. Then, the sequence generator 7 supplies the bit burst generating circuit 16 with the generation timing of the 12.5 KHz burst signal and the data indicating the generation timing of the 8 KHz signal indicating the bit signal (the password code and the key code).

The burst signal and the bit signal output from the generating circuit 16 are supplied to a synthesizing circuit 18 and synthesized with an audio signal obtained at a fixed terminal on the a side of the switch circuit 14. The output signal of the synthesizing circuit 18 is supplied to the audio-in terminal 3a of the cassette deck 3.

In the above configuration, the operation at the time of recording will be described first.

Since the switch circuit 2 is connected to the terminal a during recording, the analog audio signal SA1 supplied to the terminal 1 is supplied to the A / D converter 6 and converted into digital audio data by a sampling clock of 24 KHz. The data is sequentially written to the RAM 9.

The audio data written in the RAM 9 is read out at a clock of 32 KHz corresponding to the areas # 1 to # 12 (including the marginal portion) of the recording signal format and time-axis-compressed. At this time, 600
50 ms each of which constitutes msec audio data
The audio data for the period of t / c is rearranged by the CPU 4 in a scramble pattern corresponding to a key code randomly generated and subjected to scramble processing. Also, at this time, data at both ends of the audio data for 12 periods of 50 msec is read out with an extension of 1 msec, and data of the marginal portion is formed.

The audio data read from the RAM 9 is supplied to a D / A converter 12 and converted into an analog audio signal. At the time of recording, the switch circuit 14 is connected to the a side, so that the synthesizing circuit 18 synthesizes the analog audio signal output from the D / A converter 12 with the burst signal and the bit signal output from the generating circuit 16.

The synthesizing circuit 18 outputs a signal SA3 conforming to the above-described recording signal format.
A3 is supplied to the audio-in terminal 3a of the cassette deck 3 and recorded on a magnetic tape.

Next, the operation at the time of reproduction will be described.

At the time of reproduction, since the switch circuit 2 is connected to the side b, the reproduction signal SA2 output to the terminal 3b of the cassette deck 3 is supplied to the A / D converter 6 and
It is converted to digital data by a sampling clock of Hz. Then, only the audio data corresponding to the areas # 1 to # 12 are sequentially written to the RAM 9.

Then, # 1 to # written in the RAM 9
The audio data in the area 12 is read out at a clock of 24 KHz and expanded on the time axis. At this time,
The audio data of # 12 is rearranged in a descrambling pattern according to the key code detected by the detection circuit 11 from the reproduction signal SA2 and subjected to a descrambling process.

The audio data read from the RAM 9 is supplied to a D / A converter 12 and converted into an analog audio signal. At the time of reproduction, since the switch circuit 14 is connected to the b side, the analog audio signal SA4 output from the D / A converter 12 is output to the terminal 15.

Although not described above, in the example of FIG. 1, it is necessary for the user to operate the keyboard 17 to input a password even during reproduction. Then, the descrambling process is started only when the same code input at the time of reproduction is detected twice consecutively from the reproduction signal SA2. Thereafter, the passwords detected in three consecutive blocks are compared, and if at least two passwords match, the descrambling process is continued. The determination of the personal identification code is performed by supplying the personal identification code detected by the detection circuit 11 to the CPU 4 via the sequence generator 7.
Is determined by

A specific example of the identification of the personal identification code will be described with reference to FIG. The security code shown is a security code detected by the detection circuit 11 from the header of each block.
It is displayed in hexadecimal notation. As described above, the personal identification code is a 24-bit code, and each four bits represent each hexadecimal digit.

In the figure, the personal identification code is "25252".
No. 5 "and the reproduction starts from the point P, 4
When the security code is detected from the block No. 2, it means that the correct security code has been detected twice consecutively.
o. The descrambling process is started from block 4.

No. An incorrect password is detected from the block No. 6, but two blocks (No. 4 and No. 4).
Since the password in 5) is correct, the descrambling process is continued.

No. When the security code is detected from the block No. 8, the security code of the two blocks (No. 6 and No. 8) is incorrect, so The descrambling process is stopped from block 8. However, no. When the security code is detected from the block of No. 9, two blocks (N
o. 7, No. Since the security code of 9) is correct,
The descrambling process is restarted from block 9.

Hereinafter, for the same reason, no. 13, the descrambling process is stopped from the block of No. 13, and 17
The descrambling process is restarted from the block.

Further, even if not described above, the reproduced signal SA2 is reproduced at the time of reproduction.
When the same key code is detected twice consecutively,
The descrambling process is started with a descrambling pattern corresponding to the key code. Thereafter, the key codes detected in three consecutive blocks are compared, and if at least two key codes match, the descrambling process is continued with a descrambling pattern corresponding to the key codes.

The key code is determined by detecting the key code detected by the detection circuit 11 through the sequence generator 7.
It is supplied to the PU 4 and determined by the CPU 4. Note that the determination of the key code is performed after the descrambling process is enabled in the above-described determination of the password.

A specific example of key code determination will be described with reference to FIG. The illustrated key code is a key code detected by the detection circuit 11 from the header of each block.
It is displayed in hexadecimal notation. As described above, the key code is a 16-bit code, and each 4 bits indicates each hexadecimal digit.

In FIG. 3A, when the security code is determined, Q1
It is assumed that the descrambling process can be performed at the time point. No. When the key code is detected from the block No. 2, the same key code is detected twice consecutively. Key code "FFF" from block 2
The descrambling process is started with a descrambling pattern corresponding to “F”.

No. A key code of “8888” is detected from the block of No. 4, but two blocks (No. 2, N
o. Since the key code of 3) is “FFFF”, the descrambling process is continued with a descrambling pattern corresponding to the key code “FFFF”.

No. When the key code is detected from the block No. 6, the key code of the two blocks (No. 4 and No. 6) is “8888”. From the block No. 6, the descrambling process is performed with a descrambling pattern corresponding to the key code “8888”.

It is assumed that the descrambling process is stopped at the time point Q2 in the determination of the personal identification code, and then the descrambling process is enabled at the time point Q3. No. When a key code is detected from block 13, the same key code is
Nos. Have been detected consecutively. From the 13th block, the descrambling process is restarted with a descrambling pattern corresponding to the key code “0000”.

Further, in FIG. 3B, it is assumed that the descrambling process can be performed at Q4 in the determination of the personal identification code. No. When the key code is detected from the block No. 4, the same key code is detected twice consecutively. Key code "FF" from block 4
The descrambling process is started with a descrambling pattern corresponding to “FF”.

Next, the operation of the CPU 4 will be described with reference to FIGS.
This will be described with reference to the flowchart of FIG.

When the power is turned on, an initialization is first performed (step 31). Next, it is determined whether a password has been input from the keyboard 17 (step 3).
2) When a personal identification code is input, the personal identification code is set in a register (step 33).

Next, it is determined whether or not the reproduction key has been turned on (step 34). If not, it is determined whether or not the recording key has been turned on (step 35). If the recording key is not turned on in step 35, the process returns to step 34.

When the recording key is turned on in step 35, the CPU 4 sets a key code generated at random in the register (step 36) and sets the mode to recording (step 37).

Next, the cassette deck 3 is started in the recording mode (step 38), and the operation of the sequence generator 7 and the like is started (step 39). Then, the analog audio signal SA1 supplied to the terminal 1
Is subjected to A / D conversion at a sampling frequency of 24 KHz and written into the RAM 9 (step 40).

Then, the audio data for 12 periods obtained by dividing the audio data for 600 msec into 50 msec from the RAM 9 are rearranged and read with a clock of 32 KHz and a scramble pattern corresponding to the key code, and the time axis compression processing is performed. And a scramble process is performed (step 41). At this time, the signal of the marginal portion is formed by controlling the read address.

Then, the bit signal and the burst signal from the generating circuit 16 are added (step 42), and the resultant signal is supplied to the cassette deck 3 and recorded on the magnetic tape (step 4).
3). The operations of steps 40 to 43 are performed on the keyboard 1
7 until the stop key is turned on.

When the stop key is turned on in step 44, the cassette deck 3 is set to the stop state (step 45), and the process returns to step 32.

When the reproduction key is turned on in step 34 described above, the mode is set to reproduction (step 46), the cassette deck is started in the reproduction mode (step 47), and the sequence generator 7 and the like are started. The operation is started (step 48).

Next, a security code detected by the detection circuit 11 is loaded from the reproduced signal SA2 (step 49), and a security code detected in the next block is loaded (step 50). Then, the two consecutively detected security codes are compared with the security code input from the keyboard 17 (step 51), and it is determined whether or not the security code is unmatched (step 52). In this case, if any of the two consecutively detected passwords does not match the input password, it is determined that there is no match.

If there is no match in step 52,
Returning to step 50, the personal identification code detected from the next block is loaded, and comparison determination is similarly made in steps 51 and 52.

If there is no unmatch at step 52,
The key code detected by the detection circuit 11 is loaded from the reproduced signal SA2 (step 53), and the key code detected in the next block is loaded (step 54).
Then, two consecutively detected key codes are compared (step 55), and it is determined whether or not the key codes are unmatched (step 56). In this case, when two consecutively detected key codes do not match, it is determined that there is no match.

If there is no match in step 56,
Returning to step 54, the key code detected from the next block is loaded, and comparison determination is similarly made in steps 55 and 56.

If it is not unmatched in step 56,
A descrambling pattern is set according to the detected key code (step 57).

Then, the reproduction signal SA2 is A / D converted at a sampling frequency of 32 KHz, and only the audio data corresponding to the areas # 1 to # 12 of a certain block is written into the RAM 9 (step 58).

Then, the audio data in the areas # 1 to # 12 constituting each block is stored in the RAM 9 by 24KH.
The data is rearranged and read at the clock of z and in the descrambling pattern, and the time axis is expanded and the descrambling is performed (step 59). This allows
The descrambled analog audio signal SA4 is output to the audio-out terminal 15.

Next, the personal identification code detected from the three consecutive blocks is compared with the input personal identification code, and the key codes detected from the three consecutive blocks are compared with each other (step 60).

Next, it is determined whether or not the password is unmatched (step 61). If at least two or more passwords do not match the input password, it is determined that there is no match. When it is determined in step 61 that there is no match, the security code detected by the detection circuit 11 is loaded from the next block (step 62), and the process returns to step 60 to determine the mismatch of the security code.

If the password is not unmatched in step 61, it is determined whether or not the key code is unmatched (step 63). If at least two or more key codes do not match, it is determined to be unmatched. Step 6
When it is determined in step 3 that there is no match, the key code detected by the detection circuit 11 is loaded from the next block (step 64), and the flow returns to step 60 to determine the mismatch between the personal identification code and the key code.

As described above, when the personal identification code or the key code is unmatched, the processing of steps 57 to 59 is not performed, and the time axis expansion processing and the descrambling processing of the audio data in the areas # 1 to # 12 of the next block are performed. Operation is stopped.

If it is determined in step 63 that the key code is not unmatched, it is determined whether or not the stop key is turned on (step 65). If not, the process returns to step 57 and returns to step 57. The time axis expansion processing and the descrambling processing for the signal are continuously performed.

If the stop key has been turned on in step 65, the cassette deck 3 is stopped (step 45), and the process returns to step 32.

As described above, in the present embodiment, the audio signal can be scrambled and recorded on the magnetic tape, and can be recorded with secrecy.

Further, the audio signal is subjected to a time axis compression process to allow time to spare, whereby a header portion is provided for each block and a key code and the like are recorded simultaneously with the audio signal. The audio signal can be descrambled with a descrambling pattern corresponding to the key code, and the original audio signal can be easily reproduced.

Further, in this example, in addition to the key code, a secret code input by the user from the keyboard 17 is recorded in the header portion, and the secret code detected from the reproduction signal at the time of reproduction is the same as the secret code input by the user. Otherwise, the descramble processing operation is prevented from starting, so that only the user who recognizes the security code can reproduce the original audio signal by the descrambling processing, thereby increasing the confidentiality. Can be.

When the security code detected from the playback signal at the time of playback does not match the security code input by the user twice consecutively, the descrambling process is prevented from starting. Even if an error occurs in the security code detected from the playback signal due to a physical failure and coincides with the input security code by accident, the descrambling process will not be started unless the error is continuous. , The confidentiality by the personal identification code can be maintained well.

After the security code detected from the reproduced signal matches the security code input by the user twice consecutively and the descrambling operation is started, the security code detected in three consecutive blocks is started. When at least two or more of the passwords match the password input by the user, the descrambling process is continuously performed. Therefore, even if an error occurs in a password detected from a reproduced signal due to a physical failure such as a scratch on a magnetic tape, the descrambling process is not interrupted unless the error is continuous.

Further, in this example, when the key code detected from the reproduction signal during reproduction is not the same twice, the descrambling process based on the key code is not started and an erroneous descrambling is performed. It is possible to prevent descrambling processing by a pattern.

After the key code detected from the reproduced signal becomes the same twice in succession and the descrambling operation is started, at least two or more of the key codes detected in three consecutive blocks , The descrambling process based on the key code is performed. Therefore, even if an error occurs in a key code detected from a reproduced signal due to a physical obstacle such as a scratch on a magnetic tape, if the error is not continuous, the descrambling process based on the correct key code is interrupted. There is no.

In this example, an audio signal of 600 msec is divided into 12 periods of 50 msec each, and the scramble process is performed by rearranging them. In this case, the audio signal in each period after the rearrangement becomes discontinuous, and if recording is performed continuously as it is, signals near both ends of each period may be lost or changed due to a transient phenomenon or the like during recording and reproduction. is there. In this example, signals obtained by extending the signals at both ends are arranged at both ends of the audio signal in each period and recorded as a signal at the margin for a predetermined period, so that the signals near both ends of each period are recorded on the magnetic tape. At the time of recording / reproducing, the original audio signal can be satisfactorily reproduced by the descrambling process.

In the above-described embodiment, 600 ms
ec is divided into 12 periods of 50 msec each, and the audio signals are scrambled by rearranging them in a scramble pattern corresponding to the key code. However, the format of the scramble process is not limited to this. . However, due to the descrambling process,
It is necessary to arrange a key code in the header.

In the above embodiment, the audio signal is recorded / reproduced on / from the magnetic tape. However, the present invention is similarly applied to the case where the audio signal is recorded / reproduced on the magnetic disk or the one which is optically recorded / reproduced. be able to.

[0098]

According to the present invention, the key code is detected from the header of each block of the reproduction signal, and the audio signal of the segment is descrambled with the descramble pattern corresponding to the key code. Audio signals can be easily reproduced.

When the same key code is detected twice or more consecutively from the header portion of the reproduced signal, the descrambling process is started, and thereafter, the key code of the key code detected from the header portion of three consecutive blocks is started. When two or more key codes match, the descrambling process is continued with a descrambling pattern corresponding to the key code, so that a key code detected from a reproduced signal due to a physical obstacle such as a scratch on a magnetic tape. Even if an error occurs, if the error is not continuous, the descrambling process using the correct key code can be started and the descrambling process using the correct key code can be continued.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a recording / reproducing apparatus.

FIG. 2 is a diagram for explaining a password code determination.

FIG. 3 is a diagram for explaining key code determination.

FIG. 4 is a flowchart illustrating an operation of a CPU.

FIG. 5 is a flowchart illustrating an operation of a CPU.

FIG. 6 is a diagram illustrating a format of a recording signal.

FIG. 7 is a diagram illustrating a format of a header part.

FIG. 8 is a diagram illustrating a format of a segment part.

FIG. 9 is a diagram for explaining a rearrangement process and a signal of a marginal portion;

FIG. 10 is a diagram showing a frequency spectrum of a recording signal.

[Explanation of symbols]

 Reference Signs List 1 audio-in terminal 2, 14 switch circuit 3 cassette deck 4 CPU 6 A / D converter 7 sequence generator 9 RAM 11 bit burst detection circuit 12 D / A converter 15 audio-out terminal 16 bit burst generation circuit 17 keyboard 18 synthesis circuit

Claims (1)

(57) [Claims] An audio signal is reproduced from a recording medium in which a block including a header portion having a key code and a segment portion having an audio signal for a predetermined period scrambled according to the key code is continuously recorded. When reproducing, an audio signal reproduction method for obtaining an original audio signal by descrambling an audio signal of a segment part of the reproduction signal with a descrambling pattern corresponding to a key code detected from a header part of the reproduction signal, When the same key code is continuously detected twice or more from the header portion of the reproduction signal, the descrambling process is started, and thereafter, two of the key codes detected from the header portions of three consecutive blocks are started. When the above key codes match, the descramble pattern corresponding to the key code Reproducing system down in an audio signal, characterized in that continuing the descrambling process.