Digital transmission system, transmitter and receiver for application in transmission system and record carrier

The invention relates to a digital transmission system comprising a transmitter and a receiver for transmitting information through an information channel of a transmission environment, and for receiving information transmitted through an information channel, the transmission environment further comprising an auxiliary channel for transmitting an auxiliary signal consisting of synchronization / syne / information and additional information, wherein the transmitter comprises an input terminal for receiving information and is adapted to convert the information fed to the input terminal into a form in which it is suitable for transmitting through the information channel of the transmission environment and for receiving additional information and transmitting an auxiliary signal through the auxiliary channel. and decoding the information transmitted by the information channel and for receiving the auxiliary signal transmitted by the auxiliary channel. The invention also relates to a transmitter and a receiver for use in a transmission system and a record carrier obtained by the transmitter.

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A transmission system of the type referred to in the first paragraph is known, for example, from J. Tiatkinson's The Art of Digital Audio, Focal Press 1988. This book describes a transmission system in which the transmitter is in the form of a circuit for recording information on a magnetic record carrier. form of circuitry for reproducing information from a magnetic record carrier. In this context, it is possible to consider a connection using a stationary magnetic head for recording and reading information on and from the record carrier. Such systems are described, for example, in Chapter 9 of the above book. Chapter 9.20 of this book describes, for example, such a system known as SDAT. In such a system, a digital audio signal is recorded on a series of adjacent tracks formed or to be formed on a record carrier and stored lengthwise with respect to the record carrier, and an auxiliary signal containing an additional signal (e.g., secondary code information) is recorded on one or more auxiliary tracks forming the auxiliary channel and lying next to them. This additional information is intended, for example, for time information, data information, program numbers / music tracks /, text and possibly graphic information.

It should be noted in this connection that the invention is not limited to transmission systems providing transmission by means of magnetic record carriers. It is also possible to perform the transfer in other environments. It is possible to envisage the transmission of a digital signal by air (digital audio transmission) or transmission by optical means, for example by glass fibers, optical disks or optical tapes.

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It is an object of the invention to provide a number of measures for a transmission system, more particularly with regard to a highly specific format selection and in which additional information (secondary code information) can be transmitted by an auxiliary channel in order to achieve the highest possible degree of accuracy in receiving additional information. while maintaining the simplest possible detection of the auxiliary signal in the receiver, whereby another possibility arises of enabling specific functions in the receiver depending on the detected auxiliary signal.

To this end, the transmission system according to the invention is characterized in that the transmitter is adapted to generate an auxiliary signal in the form of successive blocks, the first and subsequent blocks being formed of first block sections containing synchronization information and second block sections. a section for containing additional information, the first block section of the first block comprising a synchronization signal and a first codeword, respectively. the second block section of the first block comprises a synchronization signal and a second codeword, respectively, the second codeword being equal to the first codeword if the second block section of the second block similarly contains additional information, and wherein the second codeword is not equal to the first codeword if the second the block section of the second block does not contain additional information.

Another embodiment of the basic idea of ​​the invention is characterized in that the first block section of the first block comprises a third codeword, a synchronization signal and a first codeword, respectively, the first block section of the second block comprising a fourth codeword, a synchronization signal and a second codeword, respectively. , wherein the third codeword is equal to the fourth codeword, if the second block section of the first block and the third block directly preceding the first block contain additional information, and wherein the third codeword is not equal to the fourth codeword, if the second block section of the first block does not contain additional information and the second block section of the third block does not contain additional information.

The idea is that on the receiving side, the third codeword can thus be used to determine the synchronization word following this third codeword. It is assumed here that the receiver has not yet been bound or is disconnected from the bound state due to a lack of additional information in the second block sections of one or more consecutive blocks. After the receiver has been bound, under the influence of the previously received third codeword, the receiver can then detect the synchronization word and the first codeword, so that better detection accuracy in block detection can be realized. The detection of the first codeword in the first block section of the first block further provides the receiver in the system with information about the fact that the second block section of the first

- 4 blocks contain additional information. If the second codeword in the first block section of the second following block is not equal to the first codeword, the receiver evaluates that the second section of the second block does not contain additional information. If the second codeword is actually equal to the first as the first codeword, the second section of the block contains additional information.

If a transmitter in the form of a circuit is used to record information on a magnetic record carrier and the receiver is in the form of a circuit for reading information from the record carrier, the second and fourth code words may be useful. During the transport of the record carrier at normal speed, but in the negative direction, the second codeword can now be used for binding in the receiver, so that the receiver is subsequently able to detect both the fourth codeword and the synchronization word following this second codeword. . Also in this case, it is assumed that the receiver has not yet been bound or disconnected from the bound state due to the lack of additional information in the second block sections of one or more consecutive blocks.

After the receiver has been bound under the influence of the first received second codeword, the receiver can then detect the synchronization word and the fourth codeword, so that better detection accuracy can be obtained when the blocks are detected.

To perform the same detection mechanism in both directions to detect the second block section containing the additional information, it is preferably assumed that the first codeword is equal to the fourth codeword. However, this is not necessary. Another possibility is to assume that the fourth codeword is equal to the inverted first codeword. Reading the first codeword in one direction of transport of the record carrier then ensures the same read word as when reading the fourth codeword in the direction opposite to the direction of transport, which also makes detection very simple.

The detection of the fourth codeword in the first block section of the second block at normal speed in the negative direction, this fourth codeword, as mentioned above preferably being equal to the first codeword, informing the receiver in the system of the fact that the second block section of the first block contains additional information. If the third codeword in the first block section of the first side is not equal to the fourth codeword, the receiver evaluates it so that the second section of the block preceding the first block does not contain additional information. Alternatively, if the third codeword is actually equal to the fourth codeword, the second section of the block preceding the first block will certainly contain the additional information.

The detection options described above are particularly useful in an embodiment of the invention in which the transmitter is adapted to alternately store additional information in the second block sections m1 of consecutive blocks and not store additional information in the second block sections m2 of successive blocks. The second block sections m2 of consecutive blocks are thus empty. When receiving these m2 blocks, the receiver may be disconnected from the link. Since the additional information in the second block section of the block is preceded and followed by the first block sections containing the corresponding third or second codeword, the receiver can be reset. Upon detecting the first or fourth codeword in these first block sections, the receiver recognizes that a second block section of the block containing additional information will follow.

If the transmitter described above is connected to record information on a magnetic record carrier, this refers to recording on the record carrier at a normal speed in the forward direction. In this case, the operation of the receiver described above relates to a situation in which the record carrier is read at normal speed in the forward or reverse direction.

Failure to record the additional signal in the second block sections m2 of successive blocks may result in the record carrier being erased at the time of recording.

The first codeword may be unequal to the third codeword. In this case, the first codeword is a q-bit digital number composed of interspersed n ones ”and nnul, and the third codeword is the inverted digital number of the first codeword, where n is an integer greater than 1 and q is an integer greater than or equal to 2. The first codeword is preferably a 10-bit digital number "1010101010" and the third codeword is a 10-bit digital number "0101010101 The synchronization word may be a 10-bit digital number, preferably equal to" 010011110 "or" 000111110 ".

The transmission system may further be characterized in that the recording means is adapted to record the signal in the second block sections of the number p of consecutive blocks, where p is greater than m1, to identify the position along the track length on the record carrier. Filling the second block sections of the odd blocks in successive blocks if m1 = m1 = p can be performed in different ways. For this purpose, the recording means can again record the information stored in the second block section of the even block, but now record it in the second block section of the next odd block.

Another option is to store random signals, such as interspersed zeros and ones, in the second block sections of the odd blocks of successive blocks.

The aim of this measure is to make it possible in the reproduction circuit to detect, for example, the beginning of recording at a fall of the record carrier transport speed which is increased with respect to normal reproduction speed, even if detecting information on the auxiliary channel is not very feasible record. To achieve this goal, this is reproductive

The apparatus further comprises an envelope detector having an input for receiving information read on at least one different track and an output for generating a control signal, the envelope detector being adapted to generate a first control signal upon detecting a time-varying amplitude envelope. the transport speed of the record carrier and for generating a second control signal when detecting an envelope having a constant amplitude in a specific time interval, wherein the output of the envelope detector is connected to the input of a control signal of the transport means for transporting the record carrier, and wherein the transport means is adapted to switch off this transport speed upon receipt of the second control signal.

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The invention is explained in more detail in the following description of exemplary embodiments with reference to the accompanying drawings, in which FIG. 1 shows an embodiment of a digital transmission system according to the invention in the form of block diagrams, FIG.

2a is a graphical representation of the serial data stream of the auxiliary signal and the content of the frames in this signal, FIG. 2b is a graphical representation of the content of blocks in this signal, FIG. 3a is a graphical representation of a sequence of successive blocks, FIG. 3c shows a graphical representation of the output signal of the integrator in the envelope detector of FIG. 5, FIG. 4 shows a block diagram of a receiver in the transmission system in the form of a read circuit, FIG. 5 block diagram of the envelope detector in the circuit of Fig. 4, Figs. 6a, 6b and 6c graphical representations of different data streams on the auxiliary channel, Fig. 7 graphical representation of the data stream on the auxiliary channel when an additional digital signal is applied, Fig. 8 block diagram circuit for reading the additional digital signal and FIG. 9 is a block diagram of the recording means.

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Giant. 1 shows an exemplary embodiment of a digital transmission system having an input terminal 1 for receiving information, for example in the form of an audio signal, of a monaural or stereo signal, this terminal 1 being connected to an input 2 in a coding unit 3. This coding unit 3 may be e.g. in the form of a subband encoder, as described in earlier Dutch patent documents no. / patent application 88 02 769 / a

No. / Patent Application No. 89 01 032 / or in European Patent Specification No. / Patent Application No. 289080 /.

In a subband encoder of this type, the audio signal is digitized and sampled and subsequently divided into a group of subband signals in a series of subband filters, which reduce the frequency of the samples. These subband signals are fed via line 4 to unit 5, where they are adapted for medium transmission. Unit 5 comprises, for example, a converter A and 10. Such a converter 8 to 10 is described, for example, in European Patent Specification No. (Patent Application 150,082). In this converter, 8-bit data is converted to TO bit codewords. Interleaving may occur. All of this is intended to allow error correction of the received information at the received end.

The environment through which the information is transmitted is in the form of a magnetic record carrier 6. Only a part of the half of the record carrier is shown in a longitudinal view.

A series of tracks up to T -j, running longitudinally along the record carrier, is marked on the record carrier 6. Traces to T_nthey are intended for recording the information supplied to the input terminal after its coding.

The device comprises a unit 5 for dividing the coded information and for guiding this divided and coded information on n outputs 7_A.χ to 7.n. These n outputs are connected to the corresponding recording heads 8_t1 to 8_andq. With the help of these recording heads, the information is recorded in the corresponding n tracks up to the record carrier.

Unit 5 has an input 9 for receiving an auxiliary signal. The auxiliary signal contains synchronization information and an additional signal. The additional signal may either be routed from the outside or may be generated inside the auxiliary signal generator 10. The additional signal means information about time and date, number of programs / music tracks /, text and possibly graphic information, as mentioned above. The unit 5 is adapted to make an auxiliary signal suitable for recording on an additional track on the record carrier 6. For this purpose, the unit has an output 7_q + 1 coupled to a recording head 8_±n + 1. Auxiliary signal data stream as provided by the unit 5 to the recording head 8_Λη + 1, is shown in Fig. 2.

Giant. 2a shows that the data stream is formed by successive frames .... Each frame contains several consecutive blocks. According to Fig. 2a, there are four blocks. The frame may end with an inter-frame gap.

Each block consists of a first block section / header / and a second block section / operational part /. The first block section of a specific first block, ie the side in the block sequence ··.,⁸q_2^{of B}n^{of B}q + 2^of ** °*^3Sa^^atj^E the third codeword cw3, the synchronization signal / or the synchronization word / 101 and the first codeword cwl in that order. The first block section of the directly following block, ie block B_{n +}^, contains a fourth codeword cw4, a synchronization word Ϊ04 and a second codeword c2 in this order. The first codeword cwl is equal to the fourth codeword cw4.

The second block section of block B_n contains an additional signal.

This is indicated schematically by hatching in this second block section. The second block section of the block^NBn + -j does not contain an additional signal and thus remains empty. I.e_of that the second codeword cw2 is not equal to the first / and second / codeword.

The fact that no additional signal is present in the second block section of the block may mean that the device erases the record carrier when this second block section is recorded. The data stream as shown in Figs. 2 and 3 is such that in each case second block sections of even blocks^Bn__Oof ⁸n, ^Bn + 2 '···· contain additional signals and that the second block sections of the odd blocks ...., ^Bn_ <jz ⁸Q + V - ·· are empty. That is, the third codeword cw3 is equal to the second codeword cw2, and that these codewords are not equal to the first / and fourth / codewords.

The data stream may look different, as will be explained with reference to Fig. 6. The first codeword (which is equal to the fourth codeword) may contain an alternating number of n ones "and zeros". For example, if the cwl code word is a 10-bit number, that code word will be 1010101010.

The third codeword cw3 / which in this case is equal to the second codeword / is inverse to the word cwl. This means that in the previous case, the code word cw3 would be equal to the 10-bit number 010101001.

The synchronization word may be selected randomly, but preferably a word is selected that occurs rarely or not at all in the auxiliary signal data stream. An example of a 10 bit sync word is 0100111110 or 0000111110. The choice of which of the two combinations of purge bits is selected for the sync word depends on the digital sum value (DSV) of the digital auxiliary signal. Thus, during the recording of the information signal on the record carrier, the recording means records the additional signals only in the second block sections of the even blocks and not in the second block sections of the odd blocks.

To register the beginning of a recording (music track), it is also ensured that certain information is also recorded in the second block sections of the odd blocks during several consecutive blocks. This is shown schematically in Fig. 3.

Giant. 3a shows a group of consecutive blocks.

In block θ_{η + χ} a new record begins. The end of the previous record may be stored in block B. In this case, both records represent an uninterrupted transmission. The end of the record may lie at an earlier point, for example in block B1₊₁. In this case, there will be a pause between the two records. Giant. 3b shows the envelope of the signal read from track T1. For blocks B _ to B, this envelope "Ba wOmm" has a size having an alternately specific amplitude and then a smaller amplitude, for example zero. From block B ^₊₄ to block

B this envelope remains high. When the envelope stays high «.QX &

after a fairly long period corresponding to x-4 blocks having two filled block sections, this indicates the beginning of a new recording / musical composition /.

The filling of the two block sections of the odd blocks can be performed in different ways. For example, the information could be located in the second block section of the block^B₊₄ repeated and stored in the second block section of block B, etc. However, it is only a matter of the second block sections of the odd blocks that are filled, regardless of what information these block sections should contain. These block sections could thus also be filled with random information, for example alternating zeros and ones.

Using the information stored on the auxiliary track Τ ^₊₁ will be further explained in the following description with reference to the description of the receiver.

Giant. 1 shows the receiver in the form of a circuit for reading information from a record carrier 6. The circuit comprises several read heads 24_and1, 14_and2, 14_and3, ...... 24_ANDn, 14_ANDn + 1, of which is

each connected to the corresponding input 15, .1, 15., 2, 25_Λ3, 1 · ϊ · .η a 15_Λη + 1 reading unit.

The unit 1,6 is adapted to convert the encoded and interleaved information, read from tracks up to T, to the original subband signals and to pass these subband signals over the bus line 17 to a subband decoder 18, which again combines the subband signals into digital / audio / signal by increasing the sampling rate, this signal being fed to output 19 after digital-to-analog conversion. Thus, to decode the signal read from the record carrier, the unit 16 must be able to deinterleave and re-convert the 10-bit channel words into 8-bit information words in order to perform error correction.

The circuit further comprises a unit 16 for reading additional information from the track T by means of a reading head 14_Λη + 2 · Unit 16 can derive a system clock signal from a signal read from a track. For this purpose, the information is read from st <

py T₄₊₁ fed to a phase-coupled PLL loop.

When the record carrier is initially read at the normal speed of reproduction of the record carrier in the inverted direction, the binding of the assembly must first be performed. This can be done with the help of the third codeword cw3 in the first block section of the first bioku, for example 8_nwhich is read, which is codeword 200 in Fig. 2b. It is then known that a second block section of the even block containing additional information will follow, and it is thus possible to find out and further process the information contained in this block section.

The processing may result in time information being obtained, which may be the elapsed time of the music track being played (relative time) or the total time (absolute time). This time information can be fed to an output 22 · This output can be connected to a display 22 on which the time can be made visible.

Alternatively, the title of the music track is derived from the information and is routed via output 21 to the display 22, so that it can be made visible here. Yet another option is the number of music tracks.

Giant. 4 shows in the form of a diagram another embodiment of the receiver of FIG. 1, in particular a part of the receiver intended for reading the signal from the track T_{n +} <j · Input 15_A.η + 1 is connected to the inputs of the phase-coupled loop PLL 30, the synchronization word detector 31, the detector 32 for detecting the first codeword cyl, the detector 33 for detecting the third codeword cw3, the envelope detector 34 and the memory 35.

The receiver further includes a central processing unit 36. If the system is bound, the central processing unit 36 ​​is informed by the phase-bound loop PLL 30 via line 40. The sync word detector 31 and the code word detector 32 can now detect the sync word 101, and the first code word cwl 102 in the first block section of the first even block B_nwhich is read. When this word is detected, they send detection signals to the central processing unit 36 ​​via lines 41 and 42.

The central processing unit 36 ​​now knows that the information content of the second block section of the even block B is fed to the memory 35 via the line 45. The central processing unit 36 ​​then generates an address sequence fed to the memory 35 via the bus line 47. This information from the second block section can now be stored in memory 35.

Under the influence of a control signal which can be fed to the central processing unit 36 ​​via input 50, a choice can be made as to which part of the information read from the second block section can be seen on display 22. The control signal fed by input 50 can be determined by the user. For display on the display 22, the information requested by the user, e.g. relative time (within the music track), address sequence fed to the memory 35 via the bus 48, is generated by the central processing unit 36 ​​under the influence of the control signal fed to the input 50. The time information is now read from the memory. 35 and, after decoding as needed, is routed to terminal 21.

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When reading the record carrier backwards at the normal reproduction speed, the device is capable of binding when it uses the second codeword cw2, i.e. the codeword 105 in Fig. 2b.

The phase-coupled loop PLL 30 then generates a detection signal along line 40 to central processing unit 36. Subsequently, the detector 31, the synchronization word (s) can detect the synchronization word 104 and the code word detector 32 the fourth code word cjj <4, i.e. the code word 103. in Fig. 2b, which is equal to the first codeword cwi . Then, both detectors 34 and 32 can generate detection signals, which are fed to the central processing unit 36 ​​via lines 41 and 42. The central processing unit 36 ​​now recognizes that the contents of the second block section of the even block, containing additional information, are provided to the terminal 15.n + 1.

The central processing unit 36 ​​recognizes that the record carrier transport device is oriented backwards and produces the same address sequence as mentioned above, but in the reverse order. This results from the fact that since the transport device of the record carrier works in the opposite direction, also the information from the second block section of the even block is fed to the input 15._andq + 1 in reverse order. However, due to the reverse order of the addresses, the information read from the second block section is stored in the correct place in the memory 35.

Deriving the music track number from the additional information at the reproduction speed of the record carrier can be used to search for different music tracks. For example, if a second music track is being played at this time and the user indicates with a control signal via input 50 his desire to listen to the fifth music track, the device conveys the record carrier at an increased speed in the forward direction. At this increased speed, the heads are 14_AND1 to 14_ANDn + 1 slightly pulled from the record carrier, so that the touch of the tape and the head does not prevent the transport of the record carrier.

Stopa T_{n + 1} it cannot now be read easily, so that the code words cjtfT and cw3, the synchronization words or the information contained in both block sections of the even blocks can be detected or read. However, in order to detect the beginning of the next music track, an envelope detector 34 is inserted. Detector 34 detects the envelope of the signal read from track T₊₁ head 14.n + 1. This envelope is indicated in Fig. 3b.

Giant. 5 shows an exemplary embodiment of the envelope detector 34 of FIG. 4. This detector comprises a top detector 60, a low pass filter 61 formed by a parallel connection of a capacitor and a resistor, an integrator 62 and a threshold detector §3. Signal read by head 14_ANDn + 1 is fed to the input of the detector 34. The top detector 60 and the low pass filter 61 form the envelope signal of Fig. 4b. This envelope signal is fed to an integrator 62. In the threshold detector 63, the signal is compared with a threshold value D. As soon as the threshold value, i. at the moment td of Fig. 3c, the threshold detector 63 generates a signal es to the driver, see Fig. 5.

For example, if the record carrier is to be transported from the second to the fifth music track at high speed, the central processing unit 36 ​​thus subtracts the cg signal three times. As soon as the computer contained in the central processing unit has read the occurrence of the control signal cs, this unit 36 ​​generates a control signal which is fed to the motor control unit 56 via line 55. Under the influence of this control signal, the high transport speed is switched off.

In this case, the record carrier could have been loaded too far. In this case, the central processing unit will apply a signal via the line 55 to the motor driver unit 56 to the driver, on the basis of which the record carrier is rewound at normal reproduction speed, but in the opposite direction.

Stopa T_{Q + 1} can now be read in the normal way by the head 15.n + 1. The gender words and sync words can thus be detected, and the information contained in the second block sections of the even blocks can be read, so that the beginning of the fifth music track can be detected. The unit has muted for the duration of this rewind. The record carrier can now be stopped so that the user can switch the playback device or the playback device switches automatically.

Searching for a previous music track, for example when a seventh music track is being played and the user wishes to listen to the second music track, is done in a similar way. The record carrier is rewound at increased speed. The envelope detector 34 detects the envelope and the computer in the central processing unit 36 ​​counts down the number of control signals cs according to FIG. 5. If the central processing unit has counted down the six control signals £ S, the increased reverse speed is switched off and a direct conversion to the playback speed in the forward direction is performed. Even in this case, the record carrier could cross the required location. The last part of the first song is then read first. The device can turn off the sound until the beginning of the second music track is detected.

Giant. 6 shows in FIG. 6a the same data stream as already described with reference to FIGS. 2 and 3. It will be clear that the second block sections in the even blocks ...., B, B .... contain additional signals, while second block sections of odd blocks ....,^Bq + 1 '···· J *^show empty. It will be appreciated that codeword02 and "103" are the same, while codeword cwl is not equal to codeword cw3. Giant. 6b shows a data stream in the number (m1) of consecutive blocks B_n, ^Bn + -, z ^Bn + 2^OF ···· 'in the second block sections of which an additional signal is contained. This is shown in the diagram of the help of the hatched sections in the second block sections 106, 107 and 10Q8. Bbk 3 ·] is the last block in a row of m2 of consecutive blocks containing empty second block sections. It will be appreciated that the third and second code words 100 and 105 / are different. The second codeword 1Q5I is now again not equal to the first codeword calThe receiver now recognizes that the second block section 107 of the block^B^₊-j also contains additional information.

Code word 110 block ^Bn + 2 J^ev in this case also equal to the second code word. If the data stream is received in the reverse order (for example when the reading of the magnetic record carrier moves backwards), the reading unit will know that the block^Bn + 1, directly preceding the block ^Bn + 2 'contains a second block section in which additional information is stored.

Giant. 6c provides yet another example and shows | m2 = 2 consecutive blocks B_n, ^Bn + 1z which do not contain additional information in the second block sections. It will be clear that the first block section of the block θ_{η +}^ now contains the third codeword cw3, the synchronization signal and again the third codeword cy3, respectively. In both data transmission devices at the normal reading speed of the record carrier, it will be apparent after detecting the code word 103, 1052 of the system that the corresponding block section 1062 <ISZ1 does not contain additional information. It should be noted in this context that the first block section of the block^Bn + .j in Fig. 6c could also be empty.

Filling or not filling the second block sections can also be used to place an additional digital signal in the auxiliary signal. If the second block section were filled, it would mean the numeric 1 in the additional signal and the empty second block section 0 ”in the additional signal. The detection of this additional signal can be performed, for example, as follows. Signal read by head 14.n + 1 / fig. 5 / is fed to a phase-linked loop 70 / FIG. 8 /. This may be the phase coupled loop 30 of Fig. 4. By dividing the clock frequency of the voltage-controlled oscillator by a certain value, the sampling frequency CP / fig. 8 /, which is fed to the level detector 71. The input of this level 71 detector is connected to

of the low pass 61, of FIG. 5. FIG. 7a shows successive blocks in a data stream. Giant. 7b shows the output signal of the low pass filter 61. FIG. 7c shows the sampling pulses CP fed to the level detector 21. The position of these sampling pulses in time and the frequency of these pulses is such that the signal level can be accurately determined in both block sections of successive blocks. Giant. 7d represents the output signal of the level detector 61. This signal corresponds to the additional signal.

It will be appreciated that the number of consecutive blocks having a block section containing an additional signal need not be such that the threshold detector 63 in Fig. 5 is activated. The maximum number of ones in the additional signal is thus limited.

Furthermore, in Fig. 5 it is possible to connect the second threshold detector 63, shown by the dashed lines in the figure, to the output of the integrator 62. Threshold D 1. ^se selects to exceed threshold D. The output of the threshold detector 63 is used to detect the beginning of a music track. The end of the record carrier can now be determined by using more than x₌4 blocks / fig. 3a and 3b / s filled with second block sections. The output signal of the detector 63 can now be used to stop the record carrier at the end of the tape, or it can be reversed automatically.

Giant. 9 shows a recording apparatus comprising a codeword generator generating a first codeword, a sync word generator generating one of two sync words based on a digital sum value (DSV) in digital information. This information is fed to a generator 81 via a line 86 from a central processing unit 84. The apparatus further includes a codeword generator 82 for generating a third codeword and a unit 83 for generating code information in the secondary code. The input of this unit is connected to the input terminal 9 / fig. 1 /. Unit 83 provides information to be included in the second block sections of the blocks. This takes place under the influence of the control signal fed to the unit by the central processing unit 84 via the line 87.

An additional signal may be applied to input 85, if available. The central processing unit 84 drives the controllable switch 88 via the line 89. The switch 88 can also occupy one of five positions depending on the control signal on the line 89. In the first position the generator 80 is connected to the output ZaQ + 1- In the second position the generator 81 is connected to the output

7.n + 1. In the third position, the generator 82 is connected to the output

ZaC + 1 · In the fourth position, the unit is connected to the output

ZxDíl · ⁱⁿ in the fifth position, the output of the lubrication oscillator 90 is connected to the output 7_A.η + 1 ·

To record the information shown in Fig. 6a in blocks B ^{and B}The n + 1 switch occupies positions 3,2,2,4,1,2,3 and 5. To record the information shown in Figs. 6b and 6c, the order of the positions of the switch 88 can then be simply derived.

To supply the additional signal, as explained with reference to Fig. 7, the central processing unit 84 generates control signals fed to the unit 87 and the switch 89 depending on the signal supplied to its input 85, so that at the right moments the second block sections are rather filled or rather unfulfilled.

It will be appreciated that for this purpose the unit 83 may comprise a memory in which the information to be contained in the second block sections may be stored separately, as required.