Re:
Hello,
Technically the CD is simply a storage medium. The files that are put on the CD count.
Music CDs bought at music stores store songs that are in the traditional, CDA format (or Compact Disc Audio format). CDA is a file type. So when you explore the CD on a PC, you'll see a list of tracks that are CDA files.
An 'MP3 CD' is just a Compact Disc with MP3 files on them. MP3 being a compressed audio format filetype. They are stored on the CD in the same way as the conventional music CD stores CDA files.
Only CD players which are specifically designed to be compatible with MP3s can play them. When a CD player plays an MP3 CD, it simply reads the data, and uses a DAC (Digital to Analogue Converter) to produce audio.
The same thing happens when a CD player reads a CDA track off of a CD. The only difference is that it is a different filetype, so the player would use a DAC to convert signals to sound, but it would have a different decoder for decoding the CDA files. A CD player would have a specific decoder designed to decode MP3 files on from an MP3 CD.
Most CD players simply read off the data from an audio CD (of any type) and convert it directly. However, there are some CD players which can buffer audio and place data into a temporary cache. A buffer allows the audio to be converted and decoded, then placed into a temporary store for a short while, before it is signalled to the speakers. This ensures that at events when a portable CD player is dropped and the disc is jolted out of it's steady revolution, the audio delivered to the earphones is an unbroken and continued stream. This is known as 'Jog-Proofing' on portable CD players. The same technology can be used in Hi-Fis and in car CD players.