charlie@oakhill.UUCP (Charlie Thompson) (12/02/89)
Can anybody tell me what the following CD subcode bits are defined as? They are: P Q R S T U V W as shown on the Signetics SAA7220 CD player chip. They are transmitted in the user status bit position in the SPDIF digital output from my Magnavox CD player. Inquring minds want to know! -Charlie Thompson
ksh@vine.vine.COM (Kent S. Harris) (12/04/89)
In article <2688@radio.oakhill.UUCP> charlie@oakhill.UUCP (Charlie Thompson) writes: >Can anybody tell me what the following CD subcode bits >are defined as? They are: P Q R S T U V W as shown... >-Charlie Thompson A CD player collects 98 consecutive frames to form a sub-code block, with eight 98-bit words. Thus the eight subcode bits (P through W). Only the P and Q bits are required in the audio CD format. The P channel contains a flag bit designating the start of a track, as well as the lead- in and lead-out areas on a disk. A lead-in signal consists of all 0s appearing just prior to the beginning of the music data. A start flag appears just prior to the start of music. During the last music track, preceeding the lead-out, a start flag appears again. That flag gives the start of lead-out and the P channel remains at 0 for 2 to 3 seconds. Following that time, a P signal of alternating 1s and 0s at a 2-Hz rate appears. These various sets of identity signals can be used by a basic player to control the optical pickup. The Q channel contains four basic kinds of information: control, address, "Q data", and cyclic redundancy check code. The control information consists of such things as number of audio channels, whether pre-emphasis should be engaged, digital copy protection, and so forth. The address informations consists of 4 bits indicating what kind of information is contained in the "Q data". The Q data consists of TOC (table of contents), track numbers, univeral product codes, international standard recording codes, and a some other stuff. Different information is contained in the Q data depending upon not only the address field, but the location (lead-in, during music, lead-out, etc). It's fairly baroque so I'm not going into detail. The other six bits (R, S, T, U, V, and W), which account for about 20 Megabytes of data, are available for video or other information. See: Journal of the Audio Engineering Society, Vol 36, No. 4, 1988 April. Have a nice day.
rob@PacBell.COM (Rob Bernardo) (12/11/89)
In article <3449@vine.vine.COM> ksh@vine.UUCP (Kent S. Harris) writes:
+ The control information
+consists of such things as number of audio channels, whether pre-emphasis
+should be engaged,
Aha! My new cd changer has an "emphasis" light, which comes on during
play of certain cd's. The manual, written in the most gawdawful "Japanglish",
mentions the light but never says what "emphasis" is. So what *is*
preemphasis?? Inquiry minds want to know.
--
Rob Bernardo ...![backbone]!pacbell!pbhyf!rob -or- rob@pbhyf.PacBell.COM
Product engineer, UNIX/C Reusable Code Library Editor, "Go `C' UNIX"
Office: (415) 823-2417 Pacific * Bell, San Ramon, California
Residence: (415) 827-4301 R BAR JB, Concord, Californiaejp@bohra.cpg.oz (Esmond Pitt) (12/15/89)
In article <6546@pbhyf.PacBell.COM> rob@PacBell.COM (Rob Bernardo) writes: >In article <3449@vine.vine.COM> ksh@vine.UUCP (Kent S. Harris) writes: >+ The control information >+consists of such things as number of audio channels, whether pre-emphasis >+should be engaged, > >Aha! My new cd changer has an "emphasis" light, which comes on during >play of certain cd's. The manual, written in the most gawdawful "Japanglish", >mentions the light but never says what "emphasis" is. So what *is* >preemphasis?? Inquiry minds want to know. Pre-emphasis is treble pre-emphasis, as seen in FM transmission, usually according to a time constant of 25us or 50us, and in cassettes; i.e. the treble is boosted during manufacture of the CD master, and correspondingly reduced by the player on playback. The CD standard allows for pre-emphasis to be either present or absent, with an indicator in the CD header; players are supposed to play disks of either kind correctly. I don't know that the pre-emphasis actually adds much fidelity to the CD process, and I have the impression that it's not widely used in CD's. -- Esmond Pitt, Computer Power Group ejp@bohra.cpg.oz -- Esmond Pitt, Computer Power Group ejp@bohra.cpg.oz