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Voxware Metavoice - Revision history
2026-06-19T08:14:42Z
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2021-12-14T14:17:02Z
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<p><b>New page</b></p><div>*Format tags: 0x62, 0x69, 0x70, 0x71, 0x72, 0x73, 0x74, 0x76, 0x77, 0x78, 0x79, 0x7A, 0x7B, 0x81, 0x181C<br />
*Samples: https://samples.mplayerhq.hu/A-codecs/VoxwareRT24-speechCodec/ https://samples.mplayerhq.hu/A-codecs/format-0x70-8klernouthausplecelp.wav https://samples.mplayerhq.hu/A-codecs/format-0x72-lernouthausplesbc12k.wav<br />
<br />
This is several families of audio codecs licensed or created by [[VoxWare]].<br />
<br />
== L&H CELP 4.8kpbs ==<br />
* Format tag: 0x70<br />
<br />
This is a typical CELP codec that expands 12 bytes of input into 160 samples divided into three subframes (54/53/53 samples).<br />
<br />
Transmitted data includes order-10 LPC filter for the whole frame and for each subframe there is also pitch and pulse information (scale and position).<br />
<br />
== L&H SBC codecs 8/12/16kbps ==<br />
* Format tags: 0x71, 0x72, 0x73<br />
<br />
This is a family of variable-bitrate sub-band coders. The codec seem to divide audio into 8 sub-bands and not all of them may be coded (the first frame contains flags signalling which sub-bands are coded).<br />
<br />
== RT24, RT28, RT29, VR12, VR18 ==<br />
* Format tags: 0x76, 0x77, 0x78, 0x181C<br />
* Bitrates: 2.4kbps, 2.8kbps, 2.98kbps, 1.2kbps (variable), 1.8kbps (variable)<br />
<br />
This is a family of order 10 LPC-based speech codecs sharing the same core. VR codecs can have variable bitrate because of four possible frame modes that take different amount of bits.<br />
<br />
RT24 frame:<br />
<br />
4 bits - some scale<br />
8 bits - pitch<br />
6 bits - pitch scale<br />
35 bits - filter coefficients (3 or 4 bits per coefficient in randomised order)<br />
1 bit - padding<br />
<br />
RT28 frame:<br />
<br />
4 bits - some scale<br />
8 bits - pitch<br />
41 bit - filter coefficients (3-5 bits per coefficient)<br />
4 bits - unknown<br />
6 bits - pitch scale<br />
1 bit - padding<br />
<br />
RT29 frame:<br />
<br />
4 bits - some scale<br />
8 bits - pitch<br />
41 bit - filter coefficients (3-5 bits per coefficient)<br />
3x3 bits - unknown<br />
5 bits - pitch scale<br />
1 bit - padding<br />
<br />
VR12 frame:<br />
<br />
2 bits - mode<br />
mode 0:<br />
7 bits - pitch<br />
6x4 bits - filter coefficients<br />
5 bits - pitch scale<br />
mode 1:<br />
3 bits - some scale<br />
7 bits - pitch<br />
6x4 bits - filter coefficients<br />
5 bits - pitch scale<br />
mode 2:<br />
4x4 bits - filter coefficients<br />
5 bits - pitch scale<br />
mode 3: nothing else (silence?)<br />
<br />
VR15 frame:<br />
<br />
2 bits - mode<br />
mode 0:<br />
7 bits - pitch<br />
8x4 bits - filter coefficients<br />
6 bits - pitch scale<br />
mode 1:<br />
3 bits - some scale<br />
7 bits - pitch<br />
8x4 bits - filter coefficients<br />
6 bits - pitch scale<br />
mode 2:<br />
6x4 bits - filter coefficients<br />
5 bits - pitch scale<br />
mode 3: nothing else (silence?)<br />
<br />
== SC3, SC6 ==<br />
* Format tags: 0x7A, 0x7B<br />
* Bitrates: 3kbps, 6kbps<br />
<br />
Common SC3 and SC6 frame data:<br />
<br />
8 bits - pitch<br />
6 bits - pitch scale<br />
4 bits - some scale<br />
44 bits - filter coefficients (5/5/5/4/5/3/5/2/5/0/5 bits per coefficient)<br />
1 bit - padding<br />
1 bit - additional data present flag<br />
<br />
In SC6 additional data format is the following:<br />
<br />
8x7 bits - another filter coefficients<br />
2x3 bits - unknown<br />
1 bit - padding<br />
1 bit - another flag (seems to be ignored)<br />
<br />
[[Category:Audio Codecs]]<br />
[[Category:Undiscovered Audio Codecs]]</div>
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