1、 STD*SMPTE RP LbL-ENGL 1777 E 8357901 000315Pi 2T7 SMPTE RECOMMENDED PRACTICE RP 161-1 999 Revision of RP 161-1995 Logic Design for Decoding Digital - Audio Control Words in D-1 Helical Data and Control Records 1 Scope This practice describes a way of decoding the digital audio control words embedd
2、ed in audio sectors of the D-1 recorded tape. By the method described, record- ings made by different interpretations of the early proposed format for D-1 data and control records can be retrieved with the least level of conflict. 2 Normative references The following standards contain provisions whi
3、ch, through reference in this text, constitute provisions of this practice. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this practice are encouraged to investigate the possibility of applying the most recent
4、 edition of the standards indicated below. ANSVSMPTE 227M-1996, Television Digital Compo- nent Recording - 19-mm Type D-1 - Helical Data and Control Records AES3-1992, Digital Audio Engineering - Serial Transmission Format for Two-Channel Linearly Represented Digital Audio Data EBU Tech 3252 (R1986)
5、 Standard for Recording Digital Television Signals on Magnetic Tape in Cassettes 3 Definitions 3.1 audio control words: Three nibble (4 bits) bytes of words named CHAN, PREF, and LNGH Page 1 of 4 pages recorded in audio sectors of the D-1 recorded tape to control modes of digital audio. Each of the
6、 four channels has a set of those words. 3.2 CHANbits: Defined in clause 5.4.1 of ANSVSMPTE 227M to specify the usage of the two input channels in an interface data stream. 3.3 PREFbits: Defined in clause 5.4.2 of ANWSMPTE 227M to specify the usage of preemphasis in the audio coding. 3.4 LNGHbits: D
7、efined in clause 5.4.3 of ANSVSMPTE 227M to specify the audio word length and the usage of the ancillary bits status, user, and validity. 3.5 BCNTbits: Defined in clause 5.5.1 of ANSIISMPTE 227M. Bit O (LSB) and bit 1 specify the number of useful data words in the current block. The format defined i
8、n ANSVSMPTE 227M is distinguished from the early proposed format by bit 2. The television standard is indi- cated by bit 3 (MSB). 3.6 V,U,C,R bits: V, U, and C bits are defined in clauses 4.3 validity bit, 4.4 user data bit, and 4.5 channel status bit of AES3. R bit is not used and is reserved for f
9、uture use. 3.7 pseudolD: In order to identify a particular type of coding and to correctly decode the re- corded signal from those that are based on dif- ferent implementations resulting from the early proposed format, implementation-specific bit se- quences on CHAN, PREF, and LNGH are used Copyrigh
10、t Q 1999 by the SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 595 W. Hartsdale Ave., White Plains, NY 10607 (914) 761-1100 Approved November 5,1999 STD-SHPTE RP 161-ENGL 2779 sl 8357401 0003757 135 E RP 161-1999 as pseudo identification patterns. In practice, use of PREF only covers almost all
11、cases. from the tape. The leftmost bit in the column is the first bit to be readfromthe recorded tape forthat word. 4 Types of early implementation 5 Suggested logic system Tables 1-3 show bit pattern of two implementations (Aand B) for CHAN, PREF, and LNGH words resulting from early proposed format
12、s. In each table, the sec- ond lefi column shows the bit pattern when retrieved Figure 1 shows a suggested logic for decoding audio control words. By this implementation, most of the early recordings can be automatically decoded. Table 1 - PREF bits implementations (early proposed format) PREF 1 Mod
13、e 0123 Type of implementation Command of A B pseudo ID Io O000 Preemphasis off (default) C O001 Unlocked (preemphasis off = default) 3 O01 1 Unlocked (res e rve d) o1 11 Unlocked (reserved) 1 O00 Preemphasis off Preemphasis off CD type CCITT type Unlocked (preemphasis off = default) C B B C 9 1 O01
14、Unlocked (preemphasis off) C 11 1 o1 1 Un I oc ked (res e wed) Unlocked (CD type) B 12 1100 CD type Unlocked (reserved) A 13 1101 Unlocked (CD type) Unlocked (reserved) A 14 1110 CCITT type Unlocked (reserved) A 15 1111 Unlocked CCITT type C * A (8): Take A (or B) type of decoding for CHAN, PREF, an
15、d LNGH. C: Cannot judge A or B by this control word. NOTE - Modes 2, 4, 5, 6, and 10 are not used when bit 2 of BCNT = O. Page 2 of 4 pages Table 2 - LNGH bits implementations (early proposed format) LNGH Type of implementation Command of Mode O123 A B pseudo ID * O O000 16+V+U+C+R C 1 0001 19+ c No
16、t used A 2 O010 18+V+C 19+c C 3 001 1 19+u Not used A 4 o1 O0 17+v+ u +c 18+V+C C 5 0101 6 0110 7 o1 11 8 1000 19+v 18+U+C 20 Not used 1010 Not used 1100 Not used Not used A 19+u C Not used A B 17+ v+ u + c 19+v 18+U+C B B 14 1110 Not used 20 B A (B): Take A (or B) type of decoding for CHAN, PREF, a
17、nd LNGH. C: Cannot judge A or B by this control word. NOTE - Modes 9, 11, 13, and 15 are not used when bit 2 of BCNT = O. Table 3 - CHAN bits implementations (eariy proposed format) Command of CHAN Type of implementation pseudo ID Mode O123 A B detector * O O000 2 channel - default C 1 0001 2 channe
18、l Un defi ne d A 2 O010 Single channel Stereop honk 3 O01 1 Prirnary/secondary 2 channel Undefined 4 o1 O0 Stereophonic Single channel C 8 1 O00 Undefined 2 channel B 12 1100 Undefined Primary/secondary 2 channel B * A (B): Take A (or B) type of decoding for CHAN, PREF, and LNGH. C: Cannot judge A o
19、r B by this control word. -1 - I NOTE - Modes 5, 6, 7, 9, 10, 11, 13, 14, and 15 are not used when bit 2 of BCNT = O. Page 3 of 4 pages PREF O000 I YES (A or B) PREF signify A type implementation of early format m I I 1101 I 1 t Alert WARNING or use Decode CHAN, Decode CHAN, further information PREF and LNGH PREF and LNGH for help from according to according to CHAN and/or LNGH EBU TECH 3252 SMPTE 227M Figure 1 - Suggested logic for decoding audio control words Page 4 of 4 pages
