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A codec listening test is a scientific study designed to compare two or more lossy audio codecs, typically with respect to perceived fidelity and/or compression efficiency.Most tests take the form of a double-blind comparison. Commonly used methods are known as "ABX" or "ABC/HR" or "MUSHRA". There are various software packages available for individuals to perform this type of testing themselves with minimal assistance.In an ABX test, the listener has to identify an unknown sample X as being A or B, with A (typically the original) and B (typically the encoded version) available for reference. The outcome of a test must be statistically significant. This setup ensures that the listener is not biased by his/her expectations, and that the outcome is not likely to be the result of chance. If sample X can't be determined reliably with a low p-value in a predetermined number of trials, then the null hypothesis can't be rejected and it can't be proved that there is a perceptible difference between samples A and B. This typically designates that the encoded version will actually be transparent to the listener.In an ABC/HR test, C is the original which is always available for reference. A and B are the original and the encoded version in randomized order. The listener must first distinguish the encoded version from the original (which is the Hidden Reference that the "HR" in ABC/HR stands for), prior to assigning a score as a subjective judgment of the quality. Different encoded versions can be compared against each other using these scores. Results
Many double-blind music listening tests have been carried out. The following table lists the results of several listening tests that have been published online. To obtain meaningful results, listening tests must compare codecs' performance at similar or indistinguishable bitrates, since the audio quality produced by any lossy encoder will be trivially improved by increasing the bitrate. If listeners can't consistently distinguish a lossy encoder's output from the uncompressed original audio, then it may be concluded that the codec has achieved transparency (data compression).Popular codecs compared in these tests include MP3, AAC (and extensions), Vorbis, Musepack, and WMA. The RealAudio Gecko, ATRAC3, QDesign, and MP3pro codecs appear in some tests, despite much lower adoption as of 2007. Many encoder and decoder implementations (both proprietary and open source) exist for some codecs, such as MP3, which is the oldest and best-known codec still in widespread use today.The Musepack and Vorbis codecs are the product of open source projects, and were designed to avoid patented algorithms; both have competed well with patented, proprietary codecs such as MP3, AAC, and WMA according to many of these listening tests.| Source | Dates | Codecs | Bitrate (kbit/s) | Implementations | Musical genres | Samples | Listeners | Winner | Comments |
|---|
| ff123 | 2001 | multiple | ~128 |
MP3: Lame 3.89beta --abr 134 -h --nspsytune --athtype 2 --lowpass 16 --ns-bass -8MP3: Xing within AudioCatalyst 2.1 128 kbit/s, high frequency mode disabled, simple stereo disabledAAC: Liquifier Pro 5.0.0 Beta 2, Build 24 streaming 128, equalization disabled, dynamics disabled, dual mono encoding disabled, audio bandwidth overridden by the program, set at 17995 HzMPC: mppenc.exe version 1.7.9c -radio -ltq_gain 10 -tmn 12 -nmt 4.8WMA8: Windows Media Player 7.1 (version 7.01.00.3055); wmadmoe.dll version 8.0.0.0371 128 kbit/sVorbis: Oggdrop RC2 for Windows 32 128 kbit/s | | 1 | 16 | Musepack and AAC | | | ff123 | October 2001-January 2002 | multiple | ~128 |
MP3: Lame 3.89beta --abr 134 -h --nspsytune --athtype 2 --ns-bass -8MP3: Xing within AudioCatalyst 2.1 128 kbit/s, high frequency mode disabled, simple stereo disabledAAC: Liquifier Pro 5.0.0 Beta 2, Build 24 streaming 128, equalization disabled, dynamics disabled, dual mono encoding disabled, audio bandwidth overridden by the program, set at 17995 HzMPC: *mppenc.exe version 1.7.9c -radio -ltq_gain 10 -tmn 12 -nmt 4.8WMA8: Windows Media Player 7.1 (version 7.01.00.3055); wmadmoe.dll version 8.0.0.0371 128 kbit/sVorbis: **Oggdrop pre-RC3 for Windows 32; from CVS (10/26/01) 128 kbit/s | Various | 3 | 25-28 | Musepack or Vorbis | | | ff123 | July 2002 | multiple | ~64 |
Ogg Vorbis 1.0 -b 64 --managedOgg Vorbis 1.0 -q 0MMJB 7.2 mp3pro 64WMA8 at 64 kbit/s (using WMP 7.1 to encode)Quicktime 6.0 MPEG-4 AAC Low complexity at 64 kbit/s | Various | 12 | 24-41 | MP3pro | Both Vorbis variants were a close second. | | Roberto Amorim | June 2003 | AAC | 128 CBR |
Psytel AACenc 2.15 -br 128Ahead/Nero 5.5.10.35 128 kbit/s CBR, high qualitySorenson Squeeze 3.5 (FhG Pro) 128 kbit/sApple QuickTime 6.3 (Apple/Dolby) 128 kbit/s high qualityFAAC 1.17b -a 64 (64 kbit/s/channel, ABR) | Various | 10 | 11-18 | QuickTime | | | Roberto Amorim | July 2003 | multiple | ~128 |
Apple QuickTime 6.3 MP4 encoder 128 kbit/s high qualityLAME MP3 Encoder 3.90.3 --alt-preset 128Musepack 1.14 --quality 4 --xlevelOgg Vorbis post-1.0 CVS -q 4.25Windows Media Audio v9 PRO bitrate-managed 2-pass VBR 128 kbit/s | Various | 12 | 14-24 | Musepack | AAC, WMA, and Vorbis tied for close second | | Roberto Amorim | September 2003 | multiple | ~64 |
Ahead/Nero 6.0.0.15 HE AAC VBR profile Streaming :: Medium, high qualityOgg Vorbis post-1.0 CVS -q 0MP3pro (from Adobe Audition 1.0) VBR quality 40, Current Codec, allow M/S and IS, allow narrowing, no CRCReal Audio Gecko (from Real Producer 9.0.1) 64 kbit/sWindows Media Audio v9 VBR quality 50QuickTime 6.3 AAC LC 64 kbit/s, Best Quality | Various | 12 | 30-43 | Nero HE AAC | This test showed that listeners preferred 128 kbit/s MP3 audio encoded by LAME to all the tested codecs at 64 kbit/s, with greater than 99% confidence:"No codec delivers the marketing plot [sic] of same quality as MP3 at half the bitrates." | | Roberto Amorim | January 2004 | MP3 | ~128 |
LAME encoder 3.95 --preset 128FhG MP3 encoder from Adobe Audition 1.0 VBR quality 40, "Current - Best" codec.Apple iTunes 4.2 MP3 112 kbit/s VBR, Highest quality, joint stereo, smart encodingGogo-no-coda 3.12 -b 128 -a -q 0Audioactive Encoder 2.04 128 kbit/s High QualityXing MP3 Encoder 1.5 VBR quality normal | Various | 12 | 11-22 | LAME | Serious issues with Xing and iTunes encodings were discovered after the test, and documented on results page. | | Roberto Amorim | February 2004 | AAC | ~128 |
Ahead/Nero AACenc v 2.6.2.0 -internet profile, high quality, LCApple iTunes 4.2 (Apple/QuickTime) 128 kbit/sCompaact! 1.2beta3 (zPlane/HHI) VBR 5, high quality, LCFAAC 1.23.5 -q 115Real Producer 10 beta (CodingTechnologies) 128 kbit/s | Various | 12 | 19-29 | iTunes | Open-source FAAC codec improved greatly since previous test | | Roberto Amorim | May 2004 | multiple | ~128 |
LAME encoder 3.96 -V5 --athaa-sensitivity 1Apple iTunes 4.2 128 kbit/s AACOgg Vorbis aoTuV tuning b2 -q 4.35Musepack 1.14b --quality 4.15 --xlevelSony Atrac3 132 kbit/sMicrosoft WMA9 Std Bitrate VBR 128 kbit/s | Various | 18 | 12-27 | aoTuV and Musepack | | | Roberto Amorim | June 2004 | multiple | 32 CBR |
LAME encoder 3.96 -b 32Nero Ahead HE AAC+PS 32 kbit/s CBR High QualityOgg Vorbis post-1.0.1CVS --managed -b 32 resampled with SSRCReal Audio 32 kbit/s stereo music codec in Helix Producer 10QDesign Music Codec 2 Pro 32 kbit/s at 32kHz, Quality modeMicrosoft WMA9 Std 32 kbit/s at 32kHzMP3pro 32 kbit/s at 32kHz, in Adobe Audition 1.5 | Various | 18 | 47-77 | Nero Digital | | | HydrogenAudio user "guruboolez" | July 2004 | multiple | ~175 |
MPC: musepack -standardMP3: LAME 3.97 alpha -V 3; -V 2Vorbis: megamix -q 6,00; -q 6,99; -q 5,50 | Classical | 18 | 1 | Musepack | | | HydrogenAudio user "guruboolez" | August 2005 | multiple | ~180 |
AAC: faac 1.24.1. Release date: end 2004 (?). Setting: -q175AAC: Nero Digital aacenc32 v.3.2.0.15. Release date: June 2005. Setting: -streaming (high/default encoder).MP3: LAME 3.97 alpha 11. Release date: July 2005. Setting: -V2 --vbr-newMPC: mppenc 1.15v. Release date: march 2005. Setting: --quality 5Vorbis: aoTuV beta 4 based on 1.1.1. Release date: July 2005. Setting: -q6,00 | Classical | 18 | 1 | aoTuV | The author reflects on substantial improvements in Vorbis encoding since his previous test (above):"Vorbis is now –thanks to Aoyumi [creator of aoTuV]– an excellent audio format for 180 kbit/s encodings (and classical music)." | | gURuBoOleZZ (French) | August 2005 | MP3 | ~96 |
AAC-LC: iTunes 4.9 / QuickTime 7.02 CBR 96MP3: LAME 3.97 alpha 11 --abr 99MPC: mppenc 1.14 --xlevel --quality 3 (or --thumb)Ogg Vorbis: aoTuV / LANCER beta 4 based on SVN 1.1.1 -q2,00WMA Standard: WMA 9.1 CBR 96 | Classic, various | 150 classical, 35 various | 1 | aoTuV and AAC tied (classical), aoTuV (various) | The author selected each participating encoder by pitting multiple encoders against one another in an initial "Darwinian phase." For example, LAME was chosen as the representative MP3 encoder because it clearly outperformed four other MP3 encoders on a subset of the full sample corpus. | | Sebastian Mares | December 2005 | multiple | ~140 (nominal 128) |
Nero AAC 3.1.0.2 VBR/Stereo - Streaming, 100-120 kbit/s [LC AAC]iTunes AAC 6.0.1.3 128 kbit/s, VBRLAME 3.97 Beta 2 -V5 --vbr-newOgg Vorbis AoTuV 4.51 Beta -q 4.25WMA Professional 9.1 Quality-Based VBR, Q50Shine 0.1.4 (Low Anchor) -b 128 | Various | 18 | 18-30 | 4-way tie (all except Shine) | "I think this test shows that with the current encoders, the quality at 128 kbit/s is very good... It's time to move to bitrates like 96 kbit/s or even lower (64 kbit/s)." | | | Sebastian Mares | November 2006 | multiple | ~48 |
Ogg Vorbis AoTuV 5 Beta -q -1WMA Professional 10 1-pass CBR, 48 kbit/sNero HE-AAC May 26 2006 -q 0.2WMA Standard 9.2 Quality-Based VBR, Q10iTunes AAC 7.0.2.16 48 kbit/s, CBR | Various | 20 | 22-34 | Nero Digital | WMA Professional and aoTuV tied for second | | Sebastian Mares | July 2007 | multiple | ~64 |
Ogg Vorbis AoTuV 5 Beta -q 0WMA Professional 10 1-pass CBR, 64 kbit/sNero HE-AAC Jul 20 2007 -q 0.24 | Various | 18 | 21-33 | Nero Digital and WMA Professional | |
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