CD-R Question

[wheelman]

If we follow the rule 1 minute = 10MB then why is it that we only get 700MB out of the CD when it says 80minutes.

I know they are two modes to burning (Audio and Data), but why the change is size. Also why cant we get the same Audio space to burn Data?

[Skillachi]

It has to do with the type of file compression/decompression used in burning so that a regular cd player can read it. Cd players can only understand certain.. formats and the way in which it is compressed or decompressed is what decides the amount of space it will take up...
somebody can explain further but thats a simple explanation

[GodKid]

from what I know... (which isn't too much ;))

It's a combo of things... liken the 700MB to 80 min like how they say a 40GB hard drive but the machine report 38 (or suppm like that)

Then add to the the difference in formats... as spoken to earlier CDA is bigger the wav, just a little bit though ... so decompress your MP3's into the highest quality wav files and check the diff in sive... comparing the size of the MP3 (pure compressed data) to the size of the wav or raw file should give you some idea why the conversion is the way it is...

Still very sketchy... will look it up and get back to you

[deakie]

yeah close...i does have a lot to do with format but also, the file system. isnt there a difference betwen aduio and data file sytems on cd's.
notice how the audio and data files are seperated before the 'burn'.
i canny remember exactly the differences but if you have a method to preformat an area, then you first have to define the area that is going to be used.
except for wavs you generally dont get to see the true audio data in in a file browser. you just get to see the name. i expect the data is more raw, so to speak, for audio. so once defined, the cd will not allow data into that region of the disc.

an example is when using a scsi disc for audio sampling/recording from a sampler. no way you even read whats there with a regular browser, and anything copied there with one wont be found.

hope this makes sense.

[Xenocrates]

Contrary to popular belief, no compression is actually done when digital audio is burned to a CD. The reason you don't get the entire space for the exact amount of data or audio time depends on the type of CD that you are burning. I've outlined them as follows:


For Audio CDs - The track time, Track Identification text, CD Album data and audio sequencing data is also encoded onto the disc. This extra information takes up whatever additional space you think is "lost" to the actual data itself. If you are familiar with C++, think of this addtional data as pointers. The data by itself is useless to the player. The player needs to reference these "pointers" to know exactly where on the disc to find a particular track, or segment of the track. This is what makes the track non-sequential. These pointers use up the extra 10 minutes (100 megabytes) that is consumed in an 80 minute CD.

For Data CDs - The CD-R/RW doesn't have a Boot-Record or a File Allocation Table like a hard disk does. Therefore, to make up for this deficiency, whenever data is written to the disc, an extra track is written that is known as a table of contents. The TOC track contains pointers to every block on the disc that has data written on it. A multisession CD-R caters for many data tracks on it. But each time a new track is written to the disc, a new Table of Contents track is written after the outermost track that contains everything from the last Table of contents, plus pointers to the new data just written. This is why older CD-Rs which do no support multisession cannot see any new data written to a disc in addition to what was already there. However, Table of Contents tracks consume a lot of space on the disc. That is why, it is best to burn your CDs using the "Disc-At-Once" feature (which assumes you have enough data to fill the entire disc). This significantly reduces the amount of space wasted on a data CD. However, again, since pointers are necessary for the table of contents tracks, the extra 100 megabytes of data is reserved for this purpose.

For VideoCD/Super Video CDs - VCD/SVCDs are written using a standard that was officially deprecated by the International Standards Organisation since Digital Video Discs (DVDs) replaced the standard. However, you may notice that the mpeg stream on VCD or SVCD is a lot bigger than the physical disc's size. This is the size of the MPEG stream if it were to be extracted from the Disc. Windows cannot "read" an encoded tack. That's why Audio CDs don't have filesizes when you view them under Windows Explorer. The VCD/SVCD standard has the audio for the video stream encoded as Digital Audio on the disc (like an Audio CD) and the video is encoded in a separate stream. If you view a VCD or SVCD disc using some kind of Disc-Imaging tool like CD-RWIN, you will notice most times that it has two tracks. One is an Audio track, and the other is a Video track. No compression takes place when an MPEG stream is written as a VCD/SVCD. The MPEG stream is actually split into two Audio channels and One video channel and then each stream is burned to the disc accordingly with pointers referencing each stream. These pointers ensure that the Audio and Video playback in synchronous harmony. These pointers again, consume an extra (reserved) 100 megabytes on the disc.


I hope this answers your question.

[wheelman]

http://www.disctronics.co.uk/technology/cd-rom/cdrom_spec.htm

check it out.

Mode 1 Sectors
--------------------------------
Mode 1 sectors are intended for the storage of computer data and contain the following fields.

Sync (12 bytes) which is used to enable the player to identify the start of each sector.
Header (4 bytes) consisting of Minutes, Seconds, Sectors and Mode (= 1).
ECC (Error Correction Code - 276 bytes), which comprises an additional level of CIRC error protection.
EDC (Error Detection Code - 4 bytes) for detecting errors to be corrected.
Mode 1 sectors are the simplest type and are used for most CD-ROM based formats which follow the Yellow Book.

Mode 2 Sectors
Mode 2 sectors are used for those formats based on CD-ROM XA and can be either Form 1 or 2.

Mode 2 Form 1 sectors contain 2048 bytes with the same ECC as Mode 1 sectors.
Mode 2 Form 2 sectors contain 2324 bytes of user data per sector, with no ECC are are suitable only for data where errors can be concealed (eg audio or video data).
Mode 2 sectors comprise the following fields:

Sync (12 bytes) which is used to enable the player to identify the start of each sector.
Header (4 bytes) consisting of Minutes, Seconds, Sectors and Mode (= 1).
Subheader (8 bytes) contains content related parameters eg data type.
ECC (Error Correction Code - 276 bytes) which comprises an additional level of CIRC error protection for Form 1 only.
EDC (Error Detection Code) for Forms 1 and 2.
Note that Mode 1 and Mode 2 Form 1 use the same error correction so can be used interchangeably, but not within the same track and preferably not on the same disc. Software used to write CD-Rs can be set for Mode 1 or Mode 2 Form 1. Almost all PCs and Macs will read Mode 2 Form 1 CD-ROMs as well as Mode 1.

Note that any CD-ROM will contain at least some Mode 1 or Mode 2 Form 1 sectors.

Capacity of a CD-ROM
--------------------------------
The capacity of a CD-ROM depends on whether it is a Mode 1 CD-ROM or Mode 2 CD-ROM XA. Assuming the maximum size is 76 minutes 30 seconds (as recommended) this means that there are 336,300 sectors on a CD-ROM. From this must be subtracted 166 sectors at the start of track 1 plus a few sectors for the file system, amounting to, say, 200 sectors leaving 336,100 sectors for user data.

Mode 1 sectors contain 2048 bytes per sector giving a total capacity of 688,332,800 bytes or 656MB (where 1 MB = 1024 * 1024).
Mode 2 sectors contain either 2048 or 2324 bytes per sector so will have a somewhat higher data capacity depending on the mix of the two types of sector.
The above assumes a CD-ROM comprising a single track in a single session. For multiple track/session discs the data capacity will be reduced.

[Xenocrates]

Devnull, the next time I see you post in the hardware section, I'm going to ignore it....
...it seems you already know the answers to your questions. ;D

[wheelman]

I'm just makin these post for the newbies who may be as curious as I am ;D

[deakie]

its good info.... :D

[Likkle_Techie]

i just read some serious info - thanks for the info guys ;)

[kknight]

It's all about compression. 1.7GB of data can be compressed and stored on a 700MB CD. The people that make the Linux Knoppix CD have done it...

[deakie]

someone just told me that in belgium, they are charging everyone tax on cd-r's when they buy it. the money goes to some musical artist society.
thats like saying, everyone is downloading music ???