Micronas SC4: Difference between revisions
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This is a simple speech codec supporting 32000, 16000, 11025 and 8000 Hz sampling rates. | This is a simple speech codec supporting 32000, 16000, 11025 and 8000 Hz sampling rates. | ||
It uses adaptive 6-point filtering and | It uses adaptive 6-point filtering and 30-byte blocks expanding into 58 samples (interleaved in case of stereo). | ||
Codec data starts with a 5-byte header followed by 30-byte data frame and after every 100 frames there's a special 4-byte marker inserted depending on sample rate: | |||
* 8000/11025 Hz -> <code>00 00 01 1B</code> | |||
* 16000/32000 Hz -> <code>00 00 02 2B</code> | |||
Each frame consists of 58 nibbles (starting from high nibble) and <code>0x55</code> sync marker at the end. | |||
Nibble is expanded into sample in the following way: | |||
diff_sign = nibble >> 3; | |||
diff = STEP_TABLE[nibble]; | |||
step = diff + (last_step >> 2); | |||
adiff = ((diff >> 11) == 0) ? ((newstep & 0x7F) + 0x80) << 7 >> (14 - (diff >> 7)) : 0; | |||
delta = diff_sign ? -adiff : adiff; | |||
new_sample = pred + delta; | |||
update weights as weight[i] * 255/256 - sign3(delta) * stored_sign[i] / 128 | |||
shift weights back, assign delta as new weight[0] | |||
update stored signs | |||
calculate new prediction from the new_sample and dot product of weights and stored signs | |||
clip and output sample | |||
Step table: | |||
0x800, 0x004, 0x087, 0x0D5, 0x111, 0x143, 0x175, 0x1A9, | |||
0x1A9, 0x175, 0x143, 0x111, 0x0D5, 0x087, 0x004, 0x800 | |||
[[Category:Audio Codecs]] | [[Category:Audio Codecs]] | ||
[[Category:Undiscovered Audio Codecs]] | [[Category:Undiscovered Audio Codecs]] | ||
Revision as of 09:40, 8 September 2022
- Codec ID: 0x350
- Samples: http://samples.libav.org/A-codecs/Micronas%20SC4/
This is a simple speech codec supporting 32000, 16000, 11025 and 8000 Hz sampling rates.
It uses adaptive 6-point filtering and 30-byte blocks expanding into 58 samples (interleaved in case of stereo).
Codec data starts with a 5-byte header followed by 30-byte data frame and after every 100 frames there's a special 4-byte marker inserted depending on sample rate:
- 8000/11025 Hz ->
00 00 01 1B - 16000/32000 Hz ->
00 00 02 2B
Each frame consists of 58 nibbles (starting from high nibble) and 0x55 sync marker at the end.
Nibble is expanded into sample in the following way:
diff_sign = nibble >> 3; diff = STEP_TABLE[nibble]; step = diff + (last_step >> 2); adiff = ((diff >> 11) == 0) ? ((newstep & 0x7F) + 0x80) << 7 >> (14 - (diff >> 7)) : 0; delta = diff_sign ? -adiff : adiff; new_sample = pred + delta; update weights as weight[i] * 255/256 - sign3(delta) * stored_sign[i] / 128 shift weights back, assign delta as new weight[0] update stored signs calculate new prediction from the new_sample and dot product of weights and stored signs clip and output sample
Step table:
0x800, 0x004, 0x087, 0x0D5, 0x111, 0x143, 0x175, 0x1A9, 0x1A9, 0x175, 0x143, 0x111, 0x0D5, 0x087, 0x004, 0x800