Sac is a state-of-the-art lossless audio compression model
Lossless audio compression is a complex problem, because PCM data is highly non-stationary and uses high sample resolution (typically >=16bit). That's why classic context modelling suffers from context dilution problems. Sac employs a simple OLS-NLMS predictor per frame including bias correction. Prediction residuals are encoded using a sophisticated bitplane coder including SSE and various forms of probability estimations. Meta-parameters of the predictor are optimized with DDS on by-frame basis. This results in a highly asymmetric codec design.
This program wouldn't exist without the help from the following people (in no particular order):
Matt Mahoney, Dmitry Shkarin, Eugene D. Shelwien, Florin Ghido, Grzegorz Ulacha
Sac uses fp64 for many internal calculations. The change of compiler options or (cpu-)platform might effect the output. Use at your own risk and for testing purposes only.
Sac v0.7.8
16 files (51.014.742 bytes) parallel on i7-13700H.
| Asymmetric encoding profiles - bits per sample (bps) is mean bps over all files | Profile | Size | Enc-time | Dec-time | bps |
|---|---|---|---|---|---|
| --normal | 26.812.987 | 00:00:41 | 00:00:30 | 8.441 | |
| --high | 26.708.465 | 00:04:55 | 00:00:52 | 8.407 | |
| --veryhigh | 26.621.497 | 00:32:04 | 00:01:04 | 8.379 | |
| --best | 26.554.323 | 05:17:19 | 00:01:05 | 8.358 |
| Comparison with other lossless audio codecs | Program | Parameters | Source |
|---|---|---|---|
| Sac v0.7.8 | --best | open | |
| OFR v5.100 | --preset max | closed | |
| paq8px_v208fix1 | -6 | open | |
| MAC v10.44 | --insane | open |
| Numbers are bits per sample (bps) | Name | Sac | OFR | paq8px | MAC |
|---|---|---|---|---|---|
| ATrain | 7.026 | 7.156 | 7.353 | 7,269 | |
| BeautySlept | 7.418 | 7.790 | 7.826 | 8,464 | |
| chanchan | 9.692 | 9.778 | 9.723 | 9,951 | |
| death2 | 5.068 | 5.465 | 5.215 | 6,213 | |
| experiencia | 10.866 | 10.915 | 10.963 | 11,005 | |
| female_speech | 4.372 | 4.498 | 4.708 | 5,190 | |
| FloorEssence | 9.081 | 9.409 | 9.488 | 9,537 | |
| ItCouldBeSweet | 8.200 | 8.310 | 8.330 | 8,531 | |
| Layla | 9.490 | 9.571 | 9.725 | 9,783 | |
| LifeShatters | 10.768 | 10.808 | 10.868 | 10,838 | |
| macabre | 8.986 | 9.026 | 9.249 | 9,172 | |
| male_speech | 4.276 | 4.256 | 4.509 | 5,255 | |
| SinceAlways | 10.344 | 10.409 | 10.455 | 10,522 | |
| thear1 | 11.379 | 11.400 | 11.474 | 11,451 | |
| TomsDiner | 6.996 | 7.108 | 7.057 | 7,432 | |
| velvet | 9.762 | 9.990 | 10.030 | 10,461 | |
| Mean | 8.358 | 8.493 | 8.561 | 8,817 |