AC-3 CD
| AC-3 CD | |
|---|---|
| File extension : |
.ac3, .cda, .wav,
|
| Type: | Audio file |
| Container for: | Audio data |
| Extended by: | Audio CD |
| Expanded to: | DVD-Audio |
| Website : | www.dolby.com |
The AC-3 CD (also Doby Digital AudioCD ) is an audio CD on which up to six channels in Dolby Digital format (AC-3) with a sampling frequency of 44.1 kHz can be stored. A similar procedure is possible with DTS content ( DTS-CD ).
technology
As a rule, audio material is encoded in AC-3 with a sampling frequency of 48 kHz, as required by the DVD-Video standard (with the exception of modern HD formats). Redbook -compliant audio CDs only have a sampling frequency of 44.1 kHz, so that a sampling rate conversion is necessary. Ideally, an AC-3 sound track can be generated directly from uncompressed sound tracks. Then the appropriate audio track must be encapsulated in a * .wav file by adding a header and footer. Eleven different combinations of the six channels can be used, whereby the end product must contain 44.1 kHz, 16 bit and 1.411 kbit / s sampling rate. This is achieved by using filler bits , as the maximum bit rate for the AC-3 is only 640 kBit / s.
The data generated in this way can then be burned onto an audio CD and played back in a CD player using a Dolby Digital decoder. Typically, the read bit stream is forwarded to an AV receiver via S / PDIF or HDMI , which does the D / A conversion. This automatically recognizes the existing data format and switches accordingly between PCM , AC-3 (or DTS). Playback and decoding on the computer is possible with suitable software (e.g. VLC media player ), but also with DVD and BluRay players. Unlike DTS, later DVD players included a suitable Dolby Digital decoder as standard, following pressure from the public and industry. Since the introduction of BluRay, AC-3 and DTS have established themselves as the standard. Up to 80 minutes of music in 5.1 surround sound can be stored on a CD.
distribution
The AC-3-CD was never sold commercially, as DVD-Audio with a choice between several sound tracks established itself. Similar to the DTS CD, it was only used very occasionally by enthusiasts, some of whom even mix surround versions (from stereo data) themselves.
advantages
- In contrast to other surround sound formats, such as the Super Audio CD or DVD-Audio , which require separate players, the AC-3-CD is compatible with most CD players and only requires a CD player with digital output and a Dolby Digital Decoder that is integrated in all home theater systems these days .
- Compared to multichannel sound, which is matrix-coded in stereo and decoded with a matrix decoder (such as Dolby Pro Logic , DTS NEO: 6 ), the AC-3-CD does not compromise on quality up to the surround sound level.
- AC-3 CDs are Red Book compliant, so they can be handled as "normal" audio CDs.
- It is easier to create your own than with DTS CDs because the encoders are cheaper to buy.
disadvantage
- When an AC-3 CD is played in normal PCM CD players , only a noise can be heard. In individual cases, loudspeakers can be damaged at high volume.
- With 640 kbit / s, Dolby Digital is technically inferior to the DTS method with a data rate of 1.234 kbit / s.
- An adaptation of the output data, e.g. B. Crossfading , dithering and equalizing is not possible with the AC-3 raw data.