Encoding surround sound at 128 kb/s or below

qduaty · 26th April 2007, 23:09

This is regarding Vorbis, Ambisonics and MPlayer.

As everyone knows, Xiph's Vorbis makes it possible to encode stereo sound at very low bitrates. It can also handle 255 channels, but they are uncoupled, so that 5.1 tracks usually take up to 300-400 kbps.

Regular surround sound track consists of speaker feeds of constant quantity. It is hard to upmix them if we have more speakers and a bit easier to downmix. This is covered by Ambisonics, which uses a small number of microphone signals. To encode planar surround sound, we only need 3 channels: mono, X and Y, and the results of decoding can be even better than the original source, because all speakers are involved in playback.

The experimental results show that when using current Vorbis codec and a dedicated Ambisonic encoder, a good encoding quality at about 130 kbps can be achieved for 5.1 sound tracks. There are also new coupling modes for Vorbis in testing phase, with even better encoding efficiency.

Tools. I have written two patches: encoder for oggenc with 5.1 support and encoder/decoder for mplayer. This way, mplayer can play files encoded Ambisonically as well as to encode 3-channel wav; it is also possible to create 3-channel sound tracks with regular lavc audio codecs with mencoder.

Binary versions for Windows as well as sources are available at http://www.ambisonia.com/Members/qduaty. Incorporating the patches into retail versions of the tools (especially MPlayer and FFdshow) will require some work and perhaps, feedback from users (who would include useless patches?). So please download these binaries or patches and test them--in case of anybody interested, I will describe some procedures here.

Binary mencoder on that page is compiled with x264 support, so it is possible to try 1CD movie encodings with it.

shon3i · 27th April 2007, 12:38

Sounds interesting to me but, HE-AAC @ 128 6ch sound very amazing, even 96kbps HE-AAC 6ch which is theoretic limit for 6ch encoding. Every between 96-128kbps for 6ch are good. Both Nero and CT AAC encoders give great results, but CT is my favourite

96-128kbps is usual bitrate for audio, so is good for 1CD encodings. Aslo AAC is standard which is acceptable of future HD players.

26th April 2007, 23:09	#1 \| Link
qduaty Registered User Join Date: Jan 2007 Posts: 3	Encoding surround sound at 128 kb/s or below This is regarding Vorbis, Ambisonics and MPlayer. As everyone knows, Xiph's Vorbis makes it possible to encode stereo sound at very low bitrates. It can also handle 255 channels, but they are uncoupled, so that 5.1 tracks usually take up to 300-400 kbps. Regular surround sound track consists of speaker feeds of constant quantity. It is hard to upmix them if we have more speakers and a bit easier to downmix. This is covered by Ambisonics, which uses a small number of microphone signals. To encode planar surround sound, we only need 3 channels: mono, X and Y, and the results of decoding can be even better than the original source, because all speakers are involved in playback. The experimental results show that when using current Vorbis codec and a dedicated Ambisonic encoder, a good encoding quality at about 130 kbps can be achieved for 5.1 sound tracks. There are also new coupling modes for Vorbis in testing phase, with even better encoding efficiency. Tools. I have written two patches: encoder for oggenc with 5.1 support and encoder/decoder for mplayer. This way, mplayer can play files encoded Ambisonically as well as to encode 3-channel wav; it is also possible to create 3-channel sound tracks with regular lavc audio codecs with mencoder. Binary versions for Windows as well as sources are available at http://www.ambisonia.com/Members/qduaty. Incorporating the patches into retail versions of the tools (especially MPlayer and FFdshow) will require some work and perhaps, feedback from users (who would include useless patches?). So please download these binaries or patches and test them--in case of anybody interested, I will describe some procedures here. Binary mencoder on that page is compiled with x264 support, so it is possible to try 1CD movie encodings with it.

27th April 2007, 12:38	#2 \| Link
shon3i BluRay Maniac Join Date: Dec 2005 Posts: 2,419	Sounds interesting to me but, HE-AAC @ 128 6ch sound very amazing, even 96kbps HE-AAC 6ch which is theoretic limit for 6ch encoding. Every between 96-128kbps for 6ch are good. Both Nero and CT AAC encoders give great results, but CT is my favourite 96-128kbps is usual bitrate for audio, so is good for 1CD encodings. Aslo AAC is standard which is acceptable of future HD players.