DTS or AC3?

Hi, some people may have noticed my previous thread, asking people to go and check out some of the DTS surround sound files on ... about which there was no discussion. The decision was made to go with DTS as opposed to AC3 because DTS files can be burnt to CD (as stereo files), and can hence be easily downloaded, burnt to a CD and dropped into any DVD player connected to a surround amplifier. But there seems to be a strong preference for AC3 files on doom9 ... and that makes me wonder _why_ .... can anyone give me any reasons why AC3 files are preferrable over DTS files? I'm trying to identify which is the best format for online distribution of ambisonic surround sounds... should this be AC3 over DTS? (and if so, why?) Etienne

Licensing costs used to be higher for DTS than Dolby Digital in the past, that's why there is less DTS content out there.

Many DVD players can't decode DTS at all, yes.

It is a requirement for a DVD-Video complient DVD player to be able to decode AC3 audio, as that is one of the Mandatory audio codecs - along with LPCM. DTS, however, is a Optional codec, with only a few DVD players actually having built-in hardware decoders. An average DVD player might have a DTS logo on it, which often means it will stream the raw DTS sream to e.g. a surround sound system via S/PDIF. Raw AC3 audio will also be able to be sent via S/PDIF to an external decoder. This is good if you have an external amplifier/surround system which can decode DTS. If you don't have an external amplifier at all then you can still listen to the AC3 audio via e.g. a TV (downmixed to stereo) as the DVD has a built in AC3 decoder. There are very few DVD players that are able to decode DTS natively - often require an external decoder. In addition, not all surround system can decode DTS either - so of the lower priced one are only capable of decoding AC3 audio. There is currently only one open source decoder library for DTS (by DTS I refer to just the DTS Digital Coherant Acoustics part), libdca (VideoLAN). However, this does enable many potential mathod of listening to DTS audio without the need for an expensive hardware decoder. For example, DTS could be decoded in VLC media player and streamed out of a S/PDIF out port as decoded LPCM straight into an amplifier or surround sound system. If "quality per bit" was relevant, then AC3 would win, as the compression algorithm is a lot more efficient that that of DTS. DTS used a ADPCM style compression algorithm which works by reducing the quantization-steps (uses vector quantization) in order to reduce the bitrate. This is relatively simple in comparision to the large amount of processing required to encode/decode AC3 audio, and so is less tasking on the CPU. The resultant file size is much larger, however is considered to be higher quality as it has undergone less processing and compression, which is why it is favoured by many audiophiles. DTS-CDs (DTS-WAV - DTS at 44.1kHz encapsulated in a WAV file, for CDs) are not that easy to play either - to playback a DTS-WAV CD one needs a CD-player that is able to detent and decode the stereo "noise" into 6 LPCM channels. As tebauna51 rightly said, there is no free DTS encoder available - not even any low-costing commercial pieces of software. This is due to the large patents placed on DTS and higher licensing costs. Nevertheless - the question is who the ambisonic audio is aimed at - if it is aimed at someone who had a proper surround sound system set-up then it is likely that they would be able to playback DTS audio as well. If it just aimed at someone who wishes to play it back on a DVD player (in stereo), then AC3. Cheers, Arite.