All audio CDs must meet a standard called Red Book. According to the Red Book audio standard, all CDs must be no longer than 74 minutes, must have no more than 99 tracks, and must have no tracks shorter than four seconds. In addition to these format standards, the audio of CDs must fit precise specifications. The sample rate of audio CDs must be 44,100 hz per second. A sample rate is the number of samples that a digital recording takes from an original recording. Higher sample rates mean a more precise recording. At 44,1000 hz per second, the sample rate of audio CDs is double what the human hear can comprehend. Audio CDs must also be encoded in linear pulse code modulation audio (LPCM), a lossless encoding method that does not degrade audio quality.
Unlike CDs, there is no set standard for DVD-Audio. This allows for greater flexibility within the format. Also adding to the DVD-Audio format is the increased storage space that DVD allows. While a CD can only hold approximately 750 MB of information, a DVD can hold 4.7 GB. For DVD-Audio this means higher sampling rates, as high as 192,000 hz, which theoretically means better sound quality. The added room of DVD also means that DVD-Audio discs can fit multiple audio tracks onto a single disc. For example, a DVD-Audio disc may have a mono, stereo and surround sound mix of an album all on one disc, while a CD can only provide one.
While DVD-Audio can provide higher sampling rates and other processes that can result in clearer audio, the results as to whether or not this results in better sounding music are not conclusive. In a study done by the Journal of Audio Engineering Society no determinable difference in audio quality was detected in a blind hearing test comparing stereo recordings from the two audio formats. For the creators of the study, they found the biggest advantage of DVD-Audio was the possibility for multiple audio mixes on one disc.
Nearly all disc drives made today support CD audio. The format is supported by all CD drives, DVD drives, HD DVD drives and Blu-ray drives made today. The compatibility of DVD-Audio is less definite. Most DVD-Audio discs contain special DVD-Video compatible information that allows them to be played in most DVD drives, but this still locks out most audio content to those without special drives that are made to be DVD-Audio compatible. The limited availability and popularity of the DVD-Audio format has limited the amount of players made that are fully compatible with the format.
As digital distribution becomes more commonplace, the argument between CD audio and DVD audio becomes less relevant. While CDs are still being mass produced to meet demand, DVD audio never entirely caught on with mainstream audiences. Instead it became a niche market item appealing to individuals with high-end audio systems. Most new releases are not released in DVD-Audio, and the number of catalog titles getting the DVD-Audio treatment has gone down in recent years.