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The purpose of the comparison page is not only to show how compression ratios and encoding times using the flac reference encoder compare to other lossless encoders, but also to compare features (for example, some coders archive only and files must be uncompressed completely before playback can start). Keep a few things in mind:

  • As far as I know, only two of the lossless encoders out there (flac and Kexis) are truly free (Shorten's license is more restrictive). Most others give out free binaries, but without access to the source, you are leaving your data to the whim of the maintainer for eternity; you have no way to port the program to another OS or fix it if it breaks. This can be a serious drawback unless the format has world-class clout (like MP3).
  • The compression ratios and times are representative only of the reference encoder. They are not indicative of the limits of all FLAC encoders or the FLAC format itself since the format is open and extensible, and anyone is free to write a better FLAC encoder. And it is almost certain that the reference encoder itself will improve.
  • Since FLAC supports streaming, it is at a slight disadvantage to the formats that don't because they don't have the extra overhead of all those frame headers.

I make an effort to keep this information as accurate as possible, but if any of the data is wrong, let me know and I'll correct it.

Reviewed encoders:

  • flac of course.
  • Kexis - An open-source source codec. Still in the alpha stage. No player or library support yet.
  • LPAC - A closed source codec. At least it's available for more than just Windows, but there's only a Winamp plugin.
  • Monkey's Audio - A closed source, Windows-only codec, with a Winamp plugin.
  • Pegasus-SPS - A closed source, Windows-only codec.
  • RKAU - A closed source, Windows-only codec.
  • Shorten - A.J. Robinson's well-known codec; source is available here.
  • WaveZIP - A closed source, Windows-only archiver. Uses the MUSICompress[tm] engine which supposedly has a patent. I used to have a link to the company that makes WaveZIP (GadgetLabs) but apparently they have gone out of business (maybe for trying to sell something that should cost nothing).
  • WavPack - A closed source, Windows-only archiver.

Encoders I couldn't get a copy of:

  • AudioPak
  • WavARC

If you take maximum compression ratio and speed out of the picture (as you will see later, most coders exhibit similar performance), here is a subjective sort based on overall "usefulness". As far as features go, having source code gives you the most freedom since you can add anything you need that is missing; besides, open source projects tend to get better faster than closed source ones. A close second (depending on the user) would be OS support or plugin support.

Codec Source Available? Plugins Available? Streamable? Seekable? Cost OS support
flac v0.9 YES YES (Winamp, XMMS) YES YES FREE ANY (source)
Shorten v2.3a YES YES (Winamp, XMMS) no no (v3 only) FREE ANY (source)
Kexis 0.2.2 YES no no no FREE ANY (source)
LPAC v1.20 (codec 2.0) no YES (Winamp only) no? YES FREE Windows/Linux/Solaris
Monkey's Audio v3.80 no YES (Winamp only) YES YES FREE Windows only
RKAU v1.06 no YES (Winamp only) no YES FREE Windows only
WavPack v3.6 no no no no FREE Windows only
WaveZIP v2 no no no no FREE (24-bit costs $) Windows only
Pegasus-SPS no no no no $39 (free trial) Windows only

The machine I used for encoding the test files is a PII-333 with 256 megs of RAM, running Windows NT 4.0 SP5. Unfortunately, Windows is the lowest-common-denominator platform for all the encoders.

The input corpus currently consists entirely of CD music tracks. In the future it may include more kinds of input (like speech, other sample rates, etc). There are 13 tracks whose genres range from death metal to pop to classical to chant.

In all tables, the results are sorted by compression ratio, which is compressed size / uncompressed size. The first table is a summary of results on all input tracks. The remaining table shows the results of the encoders on each track.

Some interesting things to note: LPAC quality settings are not too stable with -r (which allows seeking during playback) turned on. In most cases the 'normal' mode makes the smallest file, and much faster. RKAU also has a tendency to get bigger in the 'high' mode. Shorten's method for quantizing and transmitting the LPC coefficients is not very good which is the main reason why the fixed predictors runs are both smaller and faster.

Another ironic fact is that the encoders that are patented or cost money turn out to be the worst by most measures. SPS is so archane and crippled that I gave up trying to put together results for it after one track.

Encoder Encode time Compressed size Compression ratio
Monkey's Audio 3.80 (extra high)20:24.18381.85 MB0.5073
RKAU 1.06 (normal)52:53.46383.36 MB0.5093
RKAU 1.06 (high)133:25.36383.75 MB0.5098
Monkey's Audio 3.80 (high)7:45.75387.97 MB0.5154
LPAC 1.20 (-r, normal)20:49.34393.16 MB0.5223
LPAC 1.20 (-r, high)88:20.18393.12 MB0.5223
LPAC 1.20 (-r, extra high)109:27.86393.93 MB0.5234
flac 0.9 (-6)17:37.42398.19 MB0.5290
WavPack 3.6 (high)10:05.48403.70 MB0.5363
Kexis 0.2.217:17.42416.93 MB0.5539
Shorten 2.3a (-p0 -b1024)6:41.17417.24 MB0.5543
Shorten 2.3a (-p8 -b2048)9:16.47422.59 MB0.5614
WaveZIP8:24.17435.06 MB0.5780

Here are the results for each individual track.

Track Encoder Encode time Compressed size Compression ratio
Dream Theater
58.47 MB
Monkey's Audio (extra high)1:39.0843.70 MB0.7475
Monkey's Audio (high)0:41.9843.85 MB0.7500
RKAU 1.06 (high)8:12.4443.87 MB0.7503
RKAU 1.06 (normal)2:59.5643.88 MB0.7504
flac 0.9 (-6)1:24.7644.38 MB0.7590
LPAC 1.20 (-r, high)6:51.2444.42 MB0.7598
LPAC 1.20 (-r, normal)1:45.7244.44 MB0.7601
LPAC 1.20 (-r, extra high)7:50.8044.44 MB0.7601
Shorten 2.3a (-p8 -b2048)0:47.7944.74 MB0.7653
WavPack 3.6 (high)0:49.2145.37 MB0.7760
Pegasus-SPS4:45.0045.40 MB0.7765
Kexis 0.2.21:25.0446.52 MB0.7956
Shorten 2.3a (-p0 -b1024)0:34.5046.68 MB0.7984
WaveZIP0:38.9947.22 MB0.8077
Forty-six & 2
64.25 MB
Monkey's Audio (extra high)1:48.9439.30 MB0.6116
Monkey's Audio (high)0:33.4339.51 MB0.6149
RKAU 1.06 (normal)3:34.7539.93 MB0.6214
RKAU 1.06 (high)8:37.4239.97 MB0.6220
LPAC 1.20 (-r, normal)1:52.2240.57 MB0.6314
LPAC 1.20 (-r, high)7:36.5540.61 MB0.6320
LPAC 1.20 (-r, extra high)9:49.6440.71 MB0.6336
flac 0.9 (-6)1:32.1641.01 MB0.6382
WavPack 3.6 (high)0:52.3741.72 MB0.6492
Kexis 0.2.21:30.8542.75 MB0.6652
Shorten 2.3a (-p8 -b2048)0:50.2243.05 MB0.6701
Shorten 2.3a (-p0 -b1024)0:35.9343.19 MB0.6722
WaveZIP0:42.8444.52 MB0.6930
Cannibal Corpse
Mummified In Barbed Wire
33.37 MB
Monkey's Audio (extra high)0:49.2023.47 MB0.7033
Monkey's Audio (high)0:23.2523.66 MB0.7087
LPAC 1.20 (-r, normal)1:01.1623.75 MB0.7116
LPAC 1.20 (-r, high)5:13.5723.92 MB0.7168
LPAC 1.20 (-r, extra high)6:04.2723.95 MB0.7175
RKAU 1.06 (normal)1:32.2024.04 MB0.7202
RKAU 1.06 (high)3:21.7024.04 MB0.7202
flac 0.9 (-6)0:48.1724.31 MB0.7284
Shorten 2.3a (-p8 -b2048)0:27.0325.12 MB0.7525
WavPack 3.6 (high)0:28.0725.44 MB0.7621
Kexis 0.2.20:47.0726.03 MB0.7799
Shorten 2.3a (-p0 -b1024)0:19.8526.59 MB0.7966
WaveZIP0:22.2526.89 MB0.8058
Alanis Morisette
Hand In My Pocket
39.09 MB
Monkey's Audio (extra high)1:03.9822.85 MB0.5845
Monkey's Audio (high)0:25.7023.04 MB0.5893
RKAU 1.06 (high)5:54.6823.16 MB0.5925
RKAU 1.06 (normal)2:23.6323.19 MB0.5933
LPAC 1.20 (-r, normal)1:07.5823.45 MB0.6000
LPAC 1.20 (-r, high)4:47.0323.49 MB0.6008
LPAC 1.20 (-r, extra high)5:50.5323.52 MB0.6016
flac 0.9 (-6)0:55.8623.57 MB0.6028
WavPack 3.6 (high)0:31.4424.30 MB0.6217
Shorten 2.3a (-p8 -b2048)0:30.4524.72 MB0.6324
Kexis 0.2.20:55.1324.80 MB0.6345
Shorten 2.3a (-p0 -b1024)0:21.9325.33 MB0.6478
WaveZIP0:28.0525.95 MB0.6638
Gloria Estefan
45.15 MB
Monkey's Audio (extra high)1:15.7930.12 MB0.6670
Monkey's Audio (high)0:29.6830.32 MB0.6716
flac 0.9 (-6)1:06.1730.81 MB0.6824
RKAU 1.06 (high)6:52.6930.83 MB0.6828
RKAU 1.06 (normal)2:41.4230.87 MB0.6837
LPAC 1.20 (-r, normal)1:20.2931.03 MB0.6871
WavPack 3.6 (high)0:37.1531.04 MB0.6875
LPAC 1.20 (-r, high)5:33.2131.06 MB0.6879
LPAC 1.20 (-r, extra high)6:39.2831.11 MB0.6889
Shorten 2.3a (-p8 -b2048)0:35.5131.76 MB0.7033
Kexis 0.2.21:06.7531.86 MB0.7056
Shorten 2.3a (-p0 -b1024)0:24.6532.62 MB0.7223
WaveZIP0:29.4233.02 MB0.7313
White Room
53.01 MB
RKAU 1.06 (high)8:15.4634.30 MB0.6469
RKAU 1.06 (normal)3:12.9934.35 MB0.6479
Monkey's Audio (extra high)1:28.4534.65 MB0.6535
Monkey's Audio (high)0:24.1734.91 MB0.6586
LPAC 1.20 (-r, normal)1:34.1635.10 MB0.6621
flac 0.9 (-6)1:16.5035.16 MB0.6633
LPAC 1.20 (-r, high)6:39.2935.17 MB0.6633
LPAC 1.20 (-r, extra high)7:39.2835.19 MB0.6638
Shorten 2.3a (-p8 -b2048)0:40.4435.39 MB0.6676
WavPack 3.6 (high)0:44.1835.82 MB0.6758
Shorten 2.3a (-p0 -b1024)0:29.4936.39 MB0.6864
Kexis 0.2.21:13.4636.64 MB0.6911
WaveZIP0:35.7737.13 MB0.7004
Maurice Ravel
Fanfare from "L'eventail de Jeanne"
20.82 MB
RKAU 1.06 (normal)1:46.516.86 MB0.3297
RKAU 1.06 (high)3:53.546.90 MB0.3316
Monkey's Audio (extra high)0:30.307.09 MB0.3407
LPAC 1.20 (-r, normal)0:30.937.47 MB0.3586
LPAC 1.20 (-r, extra high)3:06.277.48 MB0.3591
LPAC 1.20 (-r, high)2:21.167.48 MB0.3593
Monkey's Audio (high)0:12.587.56 MB0.3634
flac 0.9 (-6)0:28.107.83 MB0.3760
WavPack 3.6 (high)0:16.117.99 MB0.3838
Shorten 2.3a (-p0 -b1024)0:07.928.16 MB0.3921
Shorten 2.3a (-p8 -b2048)0:13.888.28 MB0.3977
Kexis 0.2.20:26.888.52 MB0.4091
WaveZIP0:13.118.72 MB0.4193
Maurice Ravel
String Quartet (4th movement)
56.18 MB
Monkey's Audio (extra high)1:29.2620.87 MB0.3715
RKAU 1.06 (normal)3:51.4221.46 MB0.3820
Monkey's Audio (high)0:34.2921.55 MB0.3836
RKAU 1.06 (high)10:39.0521.56 MB0.3838
LPAC 1.20 (-r, high)6:28.1422.30 MB0.3969
LPAC 1.20 (-r, normal)1:28.0222.32 MB0.3972
LPAC 1.20 (-r, extra high)8:13.8622.38 MB0.3983
WavPack 3.6 (high)0:43.8422.53 MB0.4010
flac 0.9 (-6)1:16.3622.64 MB0.4030
Kexis 0.2.21:14.8123.42 MB0.4168
Shorten 2.3a (-p0 -b1024)0:29.3323.63 MB0.4205
Shorten 2.3a (-p8 -b2048)0:38.0525.58 MB0.4552
WaveZIP0:36.6025.84 MB0.4600
Sergei Prokofiev
Piano Concerto No.3 (3rd movement)
100.68 MB
Monkey's Audio (extra high)2:37.5434.55 MB0.3431
RKAU 1.06 (normal)6:34.9735.31 MB0.3507
Monkey's Audio (high)1:00.4735.46 MB0.3521
LPAC 1.20 (-r, high)10:12.4735.74 MB0.3549
RKAU 1.06 (high)18:34.2035.80 MB0.3555
LPAC 1.20 (-r, extra high)12:18.7935.83 MB0.3558
LPAC 1.20 (-r, normal)2:33.4336.05 MB0.3580
WavPack 3.6 (high)1:17.0637.88 MB0.3762
flac 0.9 (-6)2:14.9838.18 MB0.3792
Shorten 2.3a (-p0 -b1024)0:50.0339.34 MB0.3907
Kexis 0.2.22:12.7939.89 MB0.3962
WaveZIP1:05.6043.67 MB0.4337
Shorten 2.3a (-p8 -b2048)1:09.8645.36 MB0.4505
Frederic Chopin
Prelude No.24 in d minor
27.46 MB
Monkey's Audio (extra high)0:42.6910.53 MB0.3834
Monkey's Audio (high)0:19.6910.77 MB0.3921
LPAC 1.20 (-r, high)3:21.6110.91 MB0.3973
LPAC 1.20 (-r, normal)0:41.7910.92 MB0.3976
LPAC 1.20 (-r, extra high)3:56.3610.93 MB0.3979
RKAU 1.06 (normal)1:58.4210.97 MB0.3994
RKAU 1.06 (high)5:20.7111.21 MB0.4083
WavPack 3.6 (high)0:22.3211.52 MB0.4193
flac 0.9 (-6)0:38.4911.70 MB0.4259
Shorten 2.3a (-p0 -b1024)0:13.5612.01 MB0.4374
Kexis 0.2.20:37.6112.14 MB0.4419
WaveZIP0:18.7513.08 MB0.4765
Shorten 2.3a (-p8 -b2048)0:20.6114.39 MB0.5239
Domenico Scarlatti
Sonata K.42 (arr.Yepes for guitar)
16.39 MB
Monkey's Audio (extra high)0:25.796.96 MB0.4245
RKAU 1.06 (high)3:09.406.96 MB0.4246
RKAU 1.06 (normal)1:14.436.97 MB0.4252
Monkey's Audio (high)0:10.287.14 MB0.4356
LPAC 1.20 (-r, normal)0:25.987.27 MB0.4436
LPAC 1.20 (-r, high)2:21.307.34 MB0.4480
LPAC 1.20 (-r, extra high)3:00.917.38 MB0.4500
flac 0.9 (-6)0:22.267.38 MB0.4504
WavPack 3.6 (high)0:13.177.41 MB0.4520
Shorten 2.3a (-p0 -b1024)0:07.997.47 MB0.4558
Kexis 0.2.20:21.797.50 MB0.4572
WaveZIP0:10.567.83 MB0.4781
Shorten 2.3a (-p8 -b2048)0:10.918.20 MB0.5001
The Benedictine Monks of
Santo Domingo de Silos
Laetatus sum
24.26 MB
RKAU 1.06 (high)3:15.2912.21 MB0.5031
RKAU 1.06 (normal)1:25.4812.21 MB0.5034
Monkey's Audio (extra high)0:41.1912.47 MB0.5138
Monkey's Audio (high)0:15.6912.68 MB0.5228
LPAC 1.20 (-r, normal)0:41.2212.75 MB0.5253
LPAC 1.20 (-r, high)3:40.6512.88 MB0.5309
flac 0.9 (-6)0:34.1412.90 MB0.5318
LPAC 1.20 (-r, extra high)4:53.8112.92 MB0.5323
WavPack 3.6 (high)0:20.2113.15 MB0.5420
Shorten 2.3a (-p0 -b1024)0:12.7113.28 MB0.5475
Kexis 0.2.20:34.0413.30 MB0.5481
Shorten 2.3a (-p8 -b2048)0:17.3513.41 MB0.5527
WaveZIP0:16.3713.72 MB0.5655
L. Subramaniam
Raga Sivapriya
213.56 MB
RKAU 1.06 (high)47:18.7892.94 MB0.4351
RKAU 1.06 (normal)19:37.6893.31 MB0.4369
Monkey's Audio (extra high)5:51.9795.30 MB0.4462
Monkey's Audio (high)2:14.5497.52 MB0.4566
LPAC 1.20 (-r, high)23:13.9697.80 MB0.4579
LPAC 1.20 (-r, normal)5:46.8498.04 MB0.4590
LPAC 1.20 (-r, extra high)30:04.0698.10 MB0.4593
flac 0.9 (-6)4:59.4798.31 MB0.4603
WavPack 3.6 (high)2:50.3599.53 MB0.4660
Shorten 2.3a (-p0 -b1024)1:53.28102.54 MB0.4801
Shorten 2.3a (-p8 -b2048)2:34.37102.59 MB0.4803
Kexis 0.2.24:51.20103.57 MB0.4849
WaveZIP2:25.86107.47 MB0.5032