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
- Input: wav file with 1-16 bit sample size, mono/stereo, pcm
- Output: sac file including all input metadata
- Decoded wav file is bit for bit identical to input wav file
- MD5 of raw pcm values
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 v0.7.18
16 files (44.1Khz, stereo) - 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 | |
|---|---|---|---|---|---|
| FLAC -8 | 100.0% | 29.793.060 | 00:00:00 | 00:00:00 | 9.385 |
| --normal | 89.6% | 26.691.217 | 00:00:22 | 00:00:20 | 8.401 |
| --high | 89.1% | 26.546.317 | 00:03:42 | 00:00:50 | 8.352 |
| --veryhigh | 88.9% | 26.480.793 | 00:17:38 | 00:00:53 | 8.330 |
| --extrahigh | 88.8% | 26.453.344 | 00:48:46 | 00:00:52 | 8.322 |
| --best | 88.6% | 26.397.759 | 04:37:00 | 00:01:00 | 8.303 |
Comparison with other lossless audio codecs
| Program | Parameters | Source |
|---|---|---|
| Sac v0.7.18 | --best | open |
| OFR v5.100 | --preset max | closed |
| paq8px_v208fix1 | -6 | open |
| MP4ALS RM23 | -b -p -z3 | open |
| MAC v10.44 | -c5000 | open |
| FLAC v1.4.3 | -8 | open |
Numbers are bits per sample (bps)
| Name | Sac | OFR | paq8px | MP4ALS | MAC | FLAC |
|---|---|---|---|---|---|---|
| ATrain | 6.991 | 7.156 | 7.353 | 7.232 | 7.269 | 7.962 |
| BeautySlept | 7.089 | 7.790 | 7.826 | 8.305 | 8.464 | 10.134 |
| chanchan | 9.658 | 9.778 | 9.723 | 9.886 | 9.951 | 10.206 |
| death2 | 5.036 | 5.465 | 5.215 | 6.660 | 6.213 | 6.092 |
| experiencia | 10.825 | 10.915 | 10.963 | 10.992 | 11.005 | 11.428 |
| female_speech | 4.356 | 4.498 | 4.708 | 4.711 | 5.190 | 5.364 |
| FloorEssence | 9.034 | 9.409 | 9.488 | 9.509 | 9.537 | 10.201 |
| ItCouldBeSweet | 8.182 | 8.310 | 8.330 | 8.396 | 8.531 | 9.064 |
| Layla | 9.454 | 9.571 | 9.725 | 9.691 | 9.783 | 10.415 |
| LifeShatters | 10.748 | 10.808 | 10.868 | 10.836 | 10.838 | 11.194 |
| macabre | 8.968 | 9.026 | 9.249 | 9.076 | 9.172 | 10.043 |
| male_speech | 4.229 | 4.256 | 4.509 | 4.813 | 5.255 | 5.674 |
| SinceAlways | 10.329 | 10.409 | 10.455 | 10.473 | 10.522 | 11.254 |
| thear1 | 11.362 | 11.400 | 11.474 | 11.425 | 11.451 | 11.783 |
| TomsDiner | 6.991 | 7.108 | 7.057 | 7.268 | 7.432 | 8.572 |
| velvet | 9.595 | 9.990 | 10.030 | 10.212 | 10.461 | 10.770 |
| Mean | 8.303 | 8.493 | 8.561 | 8.718 | 8.817 | 9.385 |
| Enc-time | 04:37:00 | 00:00:09 | 00:05:37 | 00:00:15 | 00:00:01 | 00:00:00 |
| Dec-time | 00:01:00 | 00:00:02 | 00:05:40 | 00:00:13 | 00:00:01 | 00:00:00 |