Then come and correct me.
How its encoded is everything - there are two families that compete with each other: Dolby and Digital Theater Sound (DTS).
Of course, these are both surround sound formats, meaning that each speaker has its own separate audio track that is entirely independent of the others - even though the analogue Dolby Surround achieves this by a slieght of hand.
Dolby - Dolby is not just Dolby. It can be
- Dolby Surround - An analogue 2 audio channels on the media that can be decoded by a Dolby Surround device (aka as a "Pro Logic decoder") to 4 audio channels. Used on TV and VHS and even used today in Cinemas in case the Digital sound fails. More about Pro-logic decoders later. Consumer release in 1982.
- Dolby Digital (aka Dolby AC-3) - A digital - up to 5.1 channels used in DVDs, HDTV, games, etc. All 6 sound channels are independent of one another. Dolby Digital may also be implemented as 2.0 channels. The 0.1 channel is for low frequencies only and is less bandwidth than the other 5. Introduced in 1995.
- Dolby Digital Live - Something that converts any multichannel audio to Dolby Digital for playback. Found in gaming consoles, etc. Transmission is through S/PDIF.
- Dolby Digital Ex - like Dolby Digital, but the 6th channel is full spectrum. Very rare format.
- Dolby Digital Surround Ex - like Dolby Digital, but for use in cinemas and is 6.1 channels.
- Dolby TrueHD - the first of the High Definition Digital formats - so called because the maximum bit rate of the signal has been increased from 640 Kbits/sec to 18 Megabits per second and increasing the number of audio channels to 7.1 It is bit-for-bit identical to the studio master copy. Used in Blu-ray and the now defunct HD DVD - fully supported by the HDMI standard. First consumer release in 2006.
- Dolby Digital Plus - Very similar to Dolby TrueHD, but up to 6 Mbps and only up to 1.7 Mbps on Blu-ray. Fully supported by HDMI standard - in fact, it must be used. To transmit over S/PDIF means further transcoding. Can't find when it was first released, but its probably goes hand-in-hand with Blu-ray release - so say 2006.
Next blog - all about DTS.