CompuServe Messages

Have have read the XA spec a little. This is my interpretation. I beleave it correct, and suspect I will be made well aware of any errors: To clear up a detail, XA audio is written as a data track, which is read into the host system, and sent off to a decoder. The XA audio is compressed, with a selection of compression rates. The compression appears to be "lossy", since the higher the compression, the lower the bandwidth of the playback. I don't have the exact numbers at hand, but I beleave the numbers to be like this: with minimal compression, you can get 2 hours near CD stereo; with maximal compression, you get 8 hours voice quality monaural; then there is one or two steps in between. XA also allows for the interleave of "groups" (called file numbers (?) in the XA spec) of sectors. By grouping, you can have an audio group interleaved with a graphics data group. This allows you to read the graphics an audio off the disk, with the audio synchronized to the visual. Since the sectors are interleaved, you can accesses the two groups of data with minamal head movement. The drive and medai don't differentiate between these types of data, only the "file number" recorded in the sector header. It is the applications responsability to request the correct file number for the data, and to route the data accordingly. –rick