Audio fingerprints are identifiers for audio files based on the contained audio data.

MusicBrainz originally used Relatable's TRM exclusively as their only audio fingerprint technology, but due to various scalability and performance issues, and the fact that the server is closed-source and thus, not fixable, an alternative was required. MusicIPs PUID technology was chosen in March of 2006 as an efficient alternative.

PUIDs were first integrated into Picard 0.7, and have seen continuous support in the MusicBrainz Server.

Also see: How PUIDs Work and Future Proof Fingerprint.

Known Audio Fingerprinting Systems

Open source systems:

• The fingerprint in Kurt Rosenfeld's FDMF.
• Freetantrum songprint
  There is a project called freetantrum on Sourceforge. It seems to be a dead project (its home page was replaced with an advert for unrelated things in 2001), but it may be worth investigating and resurrecting the code they produced.
• MusicURI, a project trying to combine audio fingerprinting with text based search. More info on project homepage. The GPL source code is available at SourceForge.
• A possible FutureProofFingerPrint algorithm that we could code has been Proposed by Geoff Schmidt, formally of Tuneprint.
• libFooID, an audio fingerprinting library used by, and developed for foosic.

Commercial systems:

• Relatable's TRM
  The system MusicBrainz originally used. The use of TRM has since been removed from MusicBrainz.
• MusicIP's PUID (formerly MusicMagic/Predixis)
  The PUID technology has been integrated into the MusicBrainz since March 2006 and into Picard since version 0.7.0 released in July 2007. See their patent application for details on the technology.
• AudibleMagic
  This article compares business models for Philips & Audible Magic
• Philips (also licensed by SNOCAP)
  http://ismir2002.ismir.net/proceedings/02-FP04-2.pdf http://ict.ewi.tudelft.nl/pub/doets/paper027.pdf This presentation (in PDF) has a few slides on the Philips system as well:
• USC
• AudioID:
  On the Fraunhofer IDMT site, site of the AudioID company
• Shazam have their own proprietary music fingerprinting system, currently offered directly to users over the telephone.
• And possibly most ridiculously of all: The Song Tapper