Audio CD and DVD formats

Audio CD formats

There are two kinds of CD formats, audio CDs, and data CDs.

There are three kinds of CD media, "pressed" (manufactured commercially), CD-R (recordable once), and CD-RW (recordable and erasable many times).

Audio format CDs are used for storage and playback of digitized audio data, and can be played back by any audio CD player. The recordable audio CDs you can buy in stores are no different than the recordable data CDs you can buy in the same stores for a lower price-- audio format data can be written on either. The audio CDs include in their price a royalty payment for musicians, so if you plan to copy commercial music you should buy them. For non-commercial music, recordable data CDs are fine.

Most CD players will not only play the "pressed" CDs, but also music recorded in audio format on CD-Rs, but few will play music recorded in audio format on CD-RWs. It is possible, but generally pointless, to create a CD-RW in audio format. Fortunately, you can erase the CD-RW and make something else with it.

Computers can also play audio CDs, but they are generally capable of playing audio CDs from any audio format media: "pressed", CD-R, or CD-RW.

MP3 support

For computers, a variety of types of audio files have been created to save space. The standard audio format used on audio CDs is generally stored on a computer as a .wav file. The .mp3 format is a compressed format that can save lots of space compared to standard audio .wav files. The compression factor can be adjusted, but many have found that using a bit-rate setting of 128Kbps (Kilobits per second) is the sweet spot between saving space and yet still having excellant audio quality. ;Using that bit-rate setting, .mp3 files are about an order of magnitude (factor of 10) smaller than the same music in a .wav file, allowing for 10 times the music per unit of storage or bandwidth. Microsoft invented a competing format, .wma, which compresses even better, allowing smaller files than .mp3 for the same quality, but I prefer open standards supported by many vendors, without the need to pay royalties to Microsoft, so I stick with .mp3 formats. There is also the Ogg-Vorbis format, which is an open standard, but it hasn't yet caught on enough to be a particularly useful standard.

As a result of the exploding popularity of .mp3 files, some CD players now support playback of audio data from data format CDs containing .mp3 files. While this allows a CD to contain ten hours of music instead of one, some of the standalone and auto players have stated and unstated restrictions on the number of files, folders, and depth of folders that can be supported. Both MP3 CD players that I have state their limits of folders, and folder depths, and they are generous, yet one of the players will not play all the songs on one MP3 CD I have, which meets those limits, and the other will. I can only speculate that there is an unstated limit on some other measure, perhaps total number of files, because I do have many files on that CD. Most computer software used to play MP3 CDs have no such limits, so when building MP3 CDs one must understand all the limits of the device. Having only some of the limits specified makes this a trial-and-error process... rather than displaying a meaningful error, my player simply plays a subset of the songs on the CD.

It also seems that there are variations in the ability of some MP3 players to accurately play music that has been compressed with some of the standard compression techniques. What one player will play fine, another will play but with playback artifacts, that sound like skips in the music, or other noise.

Some auto manufacturers are including MP3 CD players in newer models; older models can be replaced. Some auto sound systems (especially newer ones) have line-in jacks so that portable devices can be connected. There are adapters to connect a variety of devices to auto cassette decks, or to connect to little FM transmitters so that the auto radio tuner can tune in to the devices.

Audio DVD formats

There are apparently 3 competing formats for Audio DVDs. Wikipedia has a reasonable description of them all, and points out that:
From a purely technical standpoint, the sound resolution of a DVD-Audio recording (sampled at 24-bit/96 kHz) is substantially better than a standard CD recording (which is sampled at 16-bit/44.1 kHz). However, some people report that they cannot hear a difference between DVD-Audio and CD-Audio. Furthermore, some doubt that the quality difference is large enough to justify purchasing new playback equipment and repurchasing records in DVD-Audio format.
While this was said about DVD-Audio, it appears to apply to all three formats. None of the 3 competing formats really have much of a user base at this point.
The first is called "DVD-Audio". It supports either more music, higher quality music, or more sophisticated multi-channel music. And copy protection.
The second format is called "Dual Disc," and it claims to be playable in "most" CD players, but doesn't conform to the specs of the CD, so may not play correctly in some. The media is thicker than normal CDs, so slot loading players may not work. I'd ignore this format.
The third DVD format, is called "Super Audio CD", and is really based on DVD technology, but is another "Betamax"-like format from Sony, so should be ignored.
Of course, there are also DVD data formats, on which MP3 files may be placed. There are apparently a few DVD players that will play DVD data disks containing MP3 files. You can cram lots of music on a DVD in MP3 format.
Another difficulty is that DVD data formats come in multiple varieties. DVD-R, DVD-RW, DVD+R, and DVD+RW. The latter two, from Sony, should be ignored. There is a new "dual-layer" DVD format also, for even higher capacities.