OPTICAL DISK RECORDING AND REPRODUCING DEVICE

Abstract: An optical disk recording/reproducing device that records and reproduces digital audio data by executing an interleave processing for error correction is disclosed. According to the invention, when new audio, eg musical information is recorded successively after previously recorded musical information, recording is started by digitally adding zero data for a prescribed period. Similarly, at the end of recording of the audio information, zero data are digitally added for a prescribed period so as to end recording. The present invention avoids the production of abnormal sounds at the boundary of one recorded item and a preceding or following one.

Description: This invention relates to an optical disk recording and reproducing device which uses interleave processing on digital signals for error correction and, more particularly, to a recording and reproducing device for musical information that is digitised using an optical disk as a record medium. Compact Discs or CDs wherein musical or other audio signals are converted into digital signals to be recorded thereon has been utilised as an audio source of high quality, and recording/reproducing devices for the CD have also been evolved for practical use. An optical disk recording/reproducing device, that differs from the CD, but retains recording format compatibility and in which digital audio data are recorded and reproduced using a recordable type optical disk as a record medium is disclosed for example in our preceding PCT application (application number EP-A-0.288.571). In such optical disk recording/reproducing device, as shown in fig 1 of the accompanying drawings, an opto-magnetic disk 1 in which a vertical magnetizing membrane with a magneto-optical effect is provided on a disk recording surface 12 cm in diameter is used as a record medium. Spiral tracks in the opto-magnetic disk 1 are formed by the respective pre-grounds 2 each one of which is λ/8 in depth (λ indicates the wavelength of a laser beam). In each land section between the pre-grounds 2, a pre-recorded area 4 on which pits 3 or frame signals-to-be are recorded in the circumferential direction presenting uneven shapes at regular intervals. In the centre part of the pre-recorded area 4 there is a data record area 5 where the opto-magnetic recording is performed. Also, in a lead-in section of the inner circumference of the opto-magnetic disk 1, there is provided an area called TOC (table of contents) section 6 on which various data indicating the recorded information on the disk, for example, numbers of musical pieces, starting and ending time, and so forth can be recorded. The distance from the pit 3 in one pre-recorded area 4 to the pit 3 provided in the next pre-recorded area 4 corresponds to one frame, wherein 588-channel-bit data in conformity with a CD standard can be accommodated. In the CD standard, EFM modulation (Eight to Fourteen Modulation) is adopted. That is, one frame consists of 588 channel bits, with the first 24 bits are allocated to frame synchronous signals, and 14 x 32 bits (32 symbols) are allocated to the musical information data and parity bits. The remaining bits are used by sub code data and merging bits. An error correction code called CIRC (Cross Interleave Reed-Solomon Code) supplying an interleave delay, which has a maximum of 108 frames, is performed. The CIRC error correction is executed in addition to adopting EFM modulation in the type of optical disk recording/reproducing device using the recordable opto-magnetic disk 1 in order to enable reproduction of a usual CD and to retain upwards compatibility. Though the detailed explanation is abridged, conventional CIRC error correction adapted to CD data is executed by two-series Reed-Solomon Code that includes C₁ error correction for correcting one word symbol code and C₂ error correction capable of correcting data scattered within the plural frames due to interleave. By use of this code, if erroneous data originate in the recorded data of an optical disk during reading, the error can be corrected by referring to the data placed in 108 frames before and behind the erroneous data. With reference to Fig 2(a), illustrating an analog waveform of the recorded musical information, when new musical information B is written from the time t₀ into the pre-recorded musical information part A for example. When these recorded information are reproduced, as seen from Fig 2(b) illustrating an analog waveform of the reproduced musical information, an abnormal (buchi-buchi sound) originates among the period ΔT that includes several frames before and after the time to. This abnormal sound is caused by the above-mentioned C₂ error correction. That is, since the interleave relevancy is lost in said period ΔT, the wrong correcting procedure is performed and results in the abnormal sounds as the musical information A and B are alternately output sample by sample. It is an object of the present invention to provide an optical disk recording/reproducing device that can record digital audio data which has been subject to interleave processing for error correction on the optical disk in a manner that produces no abnormal sounds at a boundary section of the audio data during reproduction. According to the present invention, there is provided an optical disk recording/reproducing device comprising: analogue to digital converting means for receiving an input analogue audio signal and outputting a digital audio signal representative thereof; encoding means for encoding the digital audio signal prior to recording thereof and to output encoded data; data processing means for executing at least an interleave process on said encoded data and outputting record data and recording/reproducing means for recording the record data on a plurality of tracks of an optical disk and for reproducing data therefrom; characterised by: control means operative in response to operation of a control key to cause at least one of a leading and a trailing part of said audio signal to consist of a null signal for a predetermined period longer than or equal to a period corresponding to the interleave length of said interleave processing. Other features and advantages of the invention will be apparent in the following description, the appending claims and the accompanying drawings. Fig 1 is a plan view with certain parts enlarged to schematically show a record surface of a recordable type optical disk. Disk 2 is an analog waveform chart of recorded and reproduced musical information illustrating an abnormal sound caused when musical information is successively recorded on a recordable type optical disk. Fig 3 is a block diagram showing an embodiment of an optical disk recording/reproducing device of the present invention. Fig 4 is a block diagram showing a construction of an encoder that constitutes the embodiment of fig 3. Fig 5 is a time chart explaining an operation of the encoder. Fig 6 is a waveform chart showing a data waveform example of a successively recorded part when musical information is successively recorded using the optical disk recording/reproducing device of the present invention. Fig 7 is a flow chart showing a control operation to start recording by the CPU in the embodiment of fig 3. Fig 8 is a flow chart showing a control operation to stop recording by said CPU. Fig 9 is a block diagram showing a modification of a reproducing system in the embodiment of fig 3. Fig 3 illustrates the structure of an optical disk recording/reproducing device in accordance with an embodiment of the present invention. Referring to fig 3, an opto-magnetic disk 1 of the type shown in fig 1 is used as a recordable type optical disk. The opto-magnetic disk 1 is rotated at a constant linear velocity by a motor 11. An optical head 12 consists of several optical parts such as a laser diode, a photodetector, a lens and a half mirror, and is controlled so that it performs writing and reading of digital audio data by irradiating a laser beam. Also, a magnet 13 for applying the external magnetic field is provided on the opposite side of the optical head 12, with the opto-magnetic disk 1 placed between them. The magnet 13 is controlled such that its polarity reverses at the time of erasure and recording. Among the RF signals (radio frequency signals) read from the opto-magnetic disk 1 by the optical head 12, signals corresponding to a pre-recorded area 4 of the opto-magnetic disk 1 are supplied to a pre-recorded signal reproducing amplifier 14, whereas signals corresponding to a TOC section 6 and a data record area 5 where the opto-magnetic recording is performed are transmitted to an opto-magnetic signal reproduction amplifier 15. From the pre-recorded signal reproduction amplifier 14, absolute time information (an address signal) is input to a microcomputer (CPU) 17 through a decoder 16. Also, an output from the opto-magnetic reproduction amplifier 15 is transmitted to a reproduced signal processing circuit 18, where de-interleave processing and other signal processing are executed thereon. Disk information recorded in the TOC section 6 is supplied to a buffer memory 19 from the reproduced signal processing circuit 18. Then, digital audio data recorded in the data record area 5 are transmitted to a digital to analog (D/A) converter 20 from the reproduced signal processing circuit 18 to be converted into analog signals, and output as reproduced audio signals from a terminal 22 through an output amplifier 21. On the other hand, at the time of recording, an analog audio signal that is to be recorded is supplied to a terminal 23. This analog audio signal is transmitted from a fader 29 through an input amplifier 24 to an analog to digital (A/D) converter 25 to be converted into digital data. The digital audio data obtained at the analog-digital converter 25 are transmitted through an encoder 26 that adds zero data to a recorded signal processing circuit 27 where the prescribed signal processing, such as data blocking, interleave processing, and addition of error correcting code is executed. The digital audio data on which prescribed signal processing is executed in the recorded signal processing circuit 27 are then transmitted to the optical head 12 through a record amplifier 28. After modulating the laser diode, these data are recorded in the data record area 5 of the prescribed track of the opto-magnetic disk 1. The following procedure is also possible. First supply the output data of the analog to digital converter (A/D) 25 to the computer 17, detecting silent parts between tunes and writing them with their tune numbers or ending time, etc to the buffer memory 19 as disk information. Then, read this information from the buffer memory 19 to have it recorded in the TOC section 6 of the opto-magnetic disk 1 just before taking out the disk 1 from the optical disk recording/reproducing device of the present embodiment. In fig 3, 17a indicates an input device for designating operation modes of the device and recording/reproducing position of the musical information. The input device 17a also includes a record key, a reproduction key, and a stop key, etc. 17b is a display device indicating recording/reproducing state of the opto-magnetic disk 1. The optical disk recording/reproducing device of the present embodiment with the aforementioned structure performs a recording operation in a following manner. When an order to start recording the musical information is given to the computer 17 by operating the record key of the input device 17a, the computer 17 first controls the encoder 26 such that it outputs zero data only for 108 frame periods corresponding to one interleave length of the interleave processing at the recorded signal processing circuit 27. Thus, zero data equivalent to one interleave length are added to the leading part of the digital audio data of audio signals incoming from the terminal 23. On this musical information, prescribed signal processing, such as interleave processing, is executed at the recorded signal processing circuit 27 in the situation where zero data equivalent to one interleave length are added to the leading part in the encoder 26 due to the control of the computer 17. By modulating the laser power of the optical head 12 with the digital data after the prescribed signal processing executed to them in the recorded signal processing circuit 27, these digital audio data to which zero data of one interleave length are added are recorded on the opto-magnetic disk 1. Further, when an order to stop recording musical information is given to the computer 17 by operating the stop key of the input device 17a, the computer 17 controls the encoder 26 such that it outputs only zero data for 108-frame period, corresponding to one interleave length, and adds zero data equivalent to one interleave length to the trailing part of the digital audio data that have been recorded on the opto-magnetic disk 1 by that time. Then, after executing the prescribed signal processing such as interleaving processing to the one interleave length zero data added to the ending part of the digital audio data, and after recording them on the opto-magnetic disk 1, the computer 17 releases the recording mode. The encoder 26 that adds zero data to the leading and trailing parts of the digital audio data by the control of the computer 17 can be embodied as the construction given in fig 4, as an example. Referring to fig 4, to one data input terminal 30, there is supplied digital audio data obtained at the analog to digital converter (A/D) 25. These digital audio data are output from an output terminal 32 through an AND gate 31. Also, to a first control input terminal 33, there is supplied a command signal to start recording from the computer 17 by operating the record key in the input device 17a. This command signal is supplied to a data input terminal of a first D type flip-flop (FF₁) 34 and to an NAND gate 35. Further, to a second control input terminal 36, is supplied a command signal to end recording from the computer 17 by operating the end key of the input device 17a. This command signal is supplied to a data input terminal of a second D type flip-flop (FF₂) 37 and to an NOR gate 43 as well as to the AND gate 31 as a gate control signal via an inverter (I₂) 38. In the encoder 26, a quartz oscillating circuit 39 oscillates at 4.3218 MHz (equivalent to the carrier frequency of EFM modulation in the CD standards), and supplies a frequency demultiplier 40 with a bit clock signal obtained as its oscillating output. The frequency demultiplier 40 forms a frame pulse, ie, a pulse of one frame-period length ie the period of 588 channel bits by dividing the bit clock by 588, and supplies the frame pulse to a counter 41. The start recording command signal is supplied to a clear input terminal of the counter 41 via the NAND gate 35, inverter (I₁) 42 and NOR gate 43, clearing the counter 41 at timing t₁ at the rising edge of the start recording command signal. Also, the stop recording command signal is supplied to the clear input terminal of the counter via the NOR gate 43, clearing the counter 41 at timing t₂ at the rising edge of the stop recording command signal. As shown in the timing chart of fig 5, the counter 41 supplies the respective clock input terminals of said first and second D type flip-flop 34, 37 with one output pulse every time it counts 108-frame pulses are supplied from the frequency demultiplier 40. The start recording command signal supplied to the data input terminal of the first D type flip-flop 34 is delayed one period (108-frame period), ie a period corresponding to one interleave length, of the output pulse of the counter 41 and becomes a negative output Q ₁. The D type flip-flop 34 supplies the NAND gate 35 with the negative output Q ₁. As shown in fig 5, the NAND gate 35 forms a gate control signal which becomes logical "0" for a period T₁ which corresponds to one interleave length from the timing t₁ at the rising edge of the start recording command signal and which is logical "1" during other periods. The NAND gate 35 supplies this gate control signal as a NAND output of the start recording command signal and the negative output Q ₁ to the AND gate 31. Similarly, the stop recording command signal supplied to the data input terminal of the second D type flip-flop 37 is delayed one period of the output pulse of the counter 41 (108-frame period), ie a period T₂ corresponding to one interleave length and becomes an affirmative output Q₂. The second D type flip-flop 37 outputs the affirmative output Q₂ from its control output terminal 44 as an actual stop recording command signal. As seen in fig 5, when digital audio data are supplied through the data input terminal 30, the AND gate 31 adds zero data to a leading part of these data for the period T₁ equivalent to one interleave length by means of the gate control signal supplied from the NAND gate 35. Also, the AND gate 31 adds zero data to the trailing part of said digital audio data for the period T₂ equivalent to one interleave length by means of the gate control signal supplied from the interleaver 38. In operation of the optical disk recording/reproducing device having the encoder 26 of the above described structure, where musical information B, a source of which is connected to the terminal 23, is recorded halfway along previously recorded musical information A on the opto-magnetic disk 1, zero data are to be recorded for a period ΔT to the boundary part of both items of musical information as shown in fig 6(a). As the period ΔT is equivalent to a 216-frame period, that is, two interleave lengths of the interleave processing for C₂ error correction, interleave processing is performed neither on data immediately before the ending point (ta) of the musical information A nor data just after the starting point (tb) of the musical information B. Accordingly, even if signal processing such as de-interleave processing is executed at the time of reproduction, data immediately before the ending point (ta) of the musical information A is not inadvertantly corrected by data of the musical information B, and data just after the starting point (tb) of the musical information B is not erroneously corrected by data of the musical information A, either. Thus, with the optical disk recording/reproducing device, it is possible to record a number of pieces of music successively on the opto-magnetic disk 1 in a record pattern free of abnormal sounds (buchi-buchi sounds) at the boundary sections of adjacent pieces. It is also possible to reproduce musical information without producing abnormal sounds from the opto-magnetic disk 1. It is to be noted that during the period ΔT when said zero data are being recorded, no sound is produced. However as the period ΔT lasts only for about several 10 ms, there is no auditory problem. As shown in fig 6(b), it is effective from an auditory standpoint to execute fade-out or fade-in control on the shaded portions before and after the recording period ΔT of the zero data round which musical information A and B are successively recorded in order to connect those musical information smoothly, without interrupting them abruptly. Such fade-out or fade-in control may be executed by digital processing at the encoder 26; however, as shown in the embodiment of fig 1, it is simplest to execute it at an analog fader 29 that is provided between the terminal 23 to which analog audio signals are input and the input amplifier 24. Besides, when the analog fader 29 is used, generation of the abnormal sounds can be reduced to a level which is too low for the listener to recognise them auditorily even if the zero data recording period ΔT is shorter than the period equivalent to the interleave length for error correction, as shown in fig 6(c). This facilitates a reduction of the silent period during the successive recording. The operating procedures at the start and end of recording including the above-mentioned fade-out, fade-in control are explained with reference to flow charts of figs 7 and 8, respectively. At the start of recording, as shown in fig 7, it is judged whether an operating input of the record key is accepted. When it is accepted, control enters the recording mode, outputting the start recording command signal. Then frame pulses are counted while outputting zero data. When the counted value of the frame pulses reaches 108, the output of zero data is ceased. After that, by executing the fade-in processing on the musical information, the recording operation proper is started. Similarly at end of recording, as shown in fig 8, it is judged whether an operating input of the stop key is accepted. When it is accepted, the stop recording command signal is outputted. After executing the fade-out processing on the musical information, frame pulses are counted while outputting zero data. When the counted value reaches 108, the output of zero data is ceased. After the recording mode is cancelled, the recording operation is over. In the present embodiment, 108 frames (17 ms) are preserved in the leading and ending part of the digital audio data, respectively, as the recording period of zero data. However it is also acceptable to record zero data for one revolution of a particular track or for a preset given period in the successive recording section in order to simplify the control program of the computer 17. If a DRAW type optical disk that does not need repeated recording is used as a record medium, the zero data recording period may be provided either on the leading part or ending part of the digital audio data. It should be noted that if zero data were added to the leading or ending part of the audio information by executing analogue muting on the incoming audio signals, there would be a risk that the muting circuit would generate noise and that the quality of musical information would be degraded. Therefore, zero data are added by digital processing by the encoder 26 in the optical disk recording/reproducing device of the present invention. In the above described embodiment, it is also possible to supply the computer 17 with the outputs of the analog to digital (A/D) converter 25, detecting silent parts between each tune, for example, and writing tune numbers, ending time, etc in the buffer memory 19 as the disk information to record them on the TOC section 6 of the opto-magnetic disk 1. This can help further to prevent abnormal sounds from occurring by detecting the successively recorded part during recording in the reproduction system, based on the information recorded on the TOC section 6 during reproduction. As is shown in fig 9, another encoder 51 and fader 52 may be added to the circuit of the reproduction system. In the drawing, when the computer 17 detects the time of the successively recorded part during recording, the output data of the encoder 51 are controlled to be zero data for a prescribed period equivalent to one interleave length. Before and after this, the fader 52 is operated so as to output reproduced audio signals to which above mentioned fade-out or fade-in processing is executed as shown in fig 6(b), (c).

Claims: An optical disk recording/reproducing device comprising: analogue to digital converting means (25) for receiving an input analogue audio signal and outputting a digital audio signal representative thereof; encoding means (26) for encoding the digital audio signal prior to recording thereof and to output encoded data; data processing means (27) for executing at least an interleave process on said encoded data and outputting record data and recording/reproducing means (12, 13, 15, 28) for recording the record data on a plurality of tracks of an optical disk (1) and for reproducing data therefrom; characterised by: control means (17) operative in response to operation of a control key (17a) to cause at least one of a leading and a trailing part of said audio signal to consist of a null signal for a predetermined period longer than or equal to a period corresponding to the interleave length of said interleave processing. A device according to claim 1 wherein said control key is a record key and said control means are operative to cause the leading part of said audio signal to consits of a null signal. A device according to claim 2 wherein said control key is a stop key and said control means are operative to cause the trailing part of said audio signal to consist of a null signal. A device according to claim 1, 2 or 3, wherein said predetermined period is longer than a period corresponding to said interleave length. A device according to claim 1, 2, 3 or 4, further comprising fading means (29) adapted to fade the input analogue audio signal and wherein said control means is adapted to control said fading means to fade said analogue audio signal to a null signal at a leading or trailing part thereof. A device according to claim 1, 2, 3, 4 or 5, wherein said control means are operative to control said encoding means to add data representative of a null signal to a leading or trailing part of said digital audio signal. A device according to claim 6, further comprising a frame counter (41) for calculating a period corresponding to said interleave length by calculating frame pulses that indicate one frame period of the digital audio signal so as to perform an operation control of said encoding means (26) with the calculated output of the frame counter (41).

Inventors: ANDO, RYO C/O SONY CORPORATION, FUJIIE, KAZUHIKO C/O SONY CORPORATION, YOSHIDA, TADAO C/O SONY CORPORATION
Applicants: SONY CORPORATION
Application year: 1987
Main classification: G11B20
IPC codes: G11B20, G11B27, G11B7