Gapless playback is the seamless playback of digital audio formats. It allows live music or consecutive tracks to be heard exactly as they are mastered, without gaps between tracks. Gapless playback is natural for compact discs or for gramophone records, but is not always available with compressed digital audio. This can be problematic for fans of music where continuity is important, such as opera, classical music, progressive rock, and electronic music. This article or section does not cite its references or sources. ... The Beatles Magical Mystery Tour as a 33 â…“ LP vinyl record A gramophone record (also phonograph record, or simply record) is an analogue sound recording medium consisting of a flat disc with an inscribed modulated spiral groove starting near the periphery and ending near the center of the disc. ... The Teatro alla Scala in Milan, Italy. ... Classical music is a term with three distinct meanings: The European tradition of music which is associated with high culture, as distinct from popular or folk forms (including works in this tradition in non-European countries). ... For the unrelated Swedish music movement, see progg. ... Electronic music is a term for music created using electronic devices. ...

Causes for Gaps

There are two main reasons why gaps occur during playback: Compression Scheme Artifacts, and Design Choice.

Compression scheme artifacts

Most lossy audio compression schemes add a small amount of silence to the beginning of a track. One reason that this happens is because many such schemes involve a time/frequency domain transform (such as an MDCT) which can introduce gaps called encoder delay. These gaps can be enlarged at decode time when a reverse-MDCT is performed, because the reverse transform will also introduce gaps (decoder delay) of its own. Another factor is the fact that transforms act on data in units of fixed-size blocks. In order for the audio signal to be encoded in its entirety, small amounts of silence are appended to the input before the transform. If the amount of padded silence is not accounted for, the padding will be decoded together with the audio data, also introducing gaps between tracks. Due to the introduction of such gaps, the playtime of the audio data is often slightly increased.^[1] The modified discrete cosine transform (MDCT) is a Fourier-related transform based on the type-IV discrete cosine transform (DCT-IV), with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset, where subsequent blocks are overlapped so that the last...

This issue is technical but also standards-related. The popular MP3 standard, for example, defines no way to record the amount of delay or padding for later removal. Also, the encoder delay may vary from encoder to encoder, making automatic removal difficult.^[2] Even if two tracks are decompressed and merged into a single track, a gap will usually remain between them. More recent compressed audio formats (such as Ogg Vorbis) have been designed to address this problem, and can therefore produce gapless audio if played back correctly. MPEG-1 Audio Layer 3, more commonly referred to as MP3, is a popular digital audio encoding and lossy compression format and algorithm, designed to greatly reduce the amount of data required to represent audio, yet still sound like a faithful reproduction of the original uncompressed audio to most listeners. ... This page is about the audio compression codec. ...

Design choice

Even when the audio file itself does not contain undesirable gaps, software/firmware/hardware design often adds gaps during playback. In some cases, software closes and re-opens the output stream when switching tracks, causing the hardware to create a very short "click". This problem is solved in more sophisticated designs of gapless playback.

A different design problem relates to software/firmware/hardware which are not ready to seamlessly move to the next track by the time the current track is complete. In this scenario, the listener is left waiting in silence as the player locates the next file, reads it, decodes the first blocks if necessary and then starts loading the buffer for playback. The gap can be as much as half a second, or even more — very noticeable in "continuous" music such as certain classical or dance genres. Unfortunately, as of October 2006, many of the current portable hard disk/flash players suffer from this problem to a greater or lesser degree, including many devices such as those from iRiver and Creative Zen, to name but a few. The Archos Gmini XS202S supports gapless playback. The Rio Karma also supports gapless playback, but is no longer manufactured. The Trekstor Vibez, released in November 2006, is based on the same firmware as the Karma and does support gapless playback. The original (with firmware update) and updated 5th Generation iPod, along with the second generation iPod nano, now support gapless playback as well. The Sony PSP also supports gapless playback. 2006 is a common year starting on Sunday of the Gregorian calendar. ... Current iriver logo iriver (formerly iRiver) Co. ... Creative Zen Vision:M 30 GB audio/video player, released in 2005. ... Archos (pronounced: ), is a French portable electronics company, (FOREX ticker ACOSF), established in 1988, by Henri Crohas. ... The Karma is a digital audio player made by Rio. ... The Trekstor Vibez is a Digital Audio Player due to be released in November 2006. ... The current iPod line. ... The iPod nano is Apples fourth digital audio player combining features of both the iPod shuffle and iPod. ...

Many older audio players on personal computers do not implement the required buffering to play gapless audio. Some of these rely on third-party gapless audio plug-ins to buffer output. Some newer players and newer versions of old players now support gapless playback directly.

Optimal solution

Where gaps are caused by the compression process, it is technically possible to store metadata with the audio to explicitly declare the amount of delay/padding introduced in the encoding process. This information can be used to ensure that playtime will remain constant after decoding with no added silence. The audio playback software must be able to recognize the metadata, and trim the decoded audio as necessary. For uncompressed audio formats this sort of information is generally redundant; the start and end of the audio is well-defined. Metadata (Greek meta after and Latin data information) are data that describe other data. ...

To address the effects of poor design, player software needs to achieve two main effects: ensuring the audio hardware itself is not stopped and started between tracks such that a click is added; and looking ahead slightly to process the next track while the current one is running, such that the data for the next track is immediately ready as the current one draws to a close.

If these areas are addressed, such that the software properly decodes the audio data and metadata, the next track is buffered and ready to play and the output stream remains open between tracks, optimal gapless audio is achieved. A collection of consecutive tracks will then play in the same way they were mastered, allowing the listener to hear their album as the author intended.

Alternative solutions

Digital signal processor (DSP) plugins can be used to detect silence between tracks and trim the audio as necessary on playback. This is not an optimal solution because it does not always produce results identical to the source. Sometimes an artist may intentionally leave silence at track boundaries for dramatic effect; removing this silence also removes that effect. A digital signal processor (DSP) is a specialized microprocessor designed specifically for digital signal processing, generally in real-time. ...

It can also be difficult to properly implement silence removal. If the silence threshold is too low and the track contains decoder artifacts, the software may not recognise some silences. Conversely, if the threshold is too high, the software may remove entire sections of quiet music at the beginning or end of a track.

DSP plugins can also be used to cross-fade between tracks. This eliminates gaps that some listeners find distracting, but also greatly alters the audio data and is not always desirable. In particular, when tracks are meant to be played together and perform the transition at high volume, cross-fading results in a large volume drop. In audio engineering, a fade is a gradual increase or decrease in the volume of a source, such as when a song is gradually reduced to silence at its end (fade-out), or gradually increases from silence at the beginning (fade-in). ...

Both of these alternate solutions are typically used to address compression methods that do not support the metadata for gapless playback. Like the optimal solution, they still require buffering and not closing the output stream; however, they require more computations, making them less efficient. In portable digital audio players, this can mean a reduced playing time on batteries.

Due to the drawbacks of the alternative solutions above, some listeners dislike their negative effects more than the gap they attempt to remove. Another problem is that the solutions above do nothing to prevent the output stream from being closed and reopened at track boundaries; some measures can be taken to simulate a gapless output stream, but they are not always successful and side-effects may occur.

Another alternative is to ignore track boundaries, encoding a single collection of tracks as a single compressed file, relying on cue sheets (or something similar) for navigation. While this method results in gapless playback within the collection of tracks with consecutive playback, it can be unwieldy due to the possibly large size of the resulting compressed file. Furthermore, unless the playback software or hardware can recognize the cue sheets, navigating between tracks may be difficult. A cue sheet, or cue file, is an ASCII (plain text) file that specifies how the tracks of a compact disc should be laid out. ...

Format support

• Since lossless data compression excludes the possibility of the introduction of padding, all lossless audio file formats are inherently gapless.
• The following lossy audio file formats have provisions for gapless encoding.
  • Musepack
  • Ogg Vorbis
  • Speex
  • Windows Media Audio
• Some other formats do not officially support gapless encoding, but some implementations of encoders or decoders may handle gapless metadata.
  • LAME-encoded MP3 can be gapless with players that support the LAME Mp3 info tag.
  • AAC in MP4 encoded with Nero Digital from Nero AG can be gapless with foobar2000 or latest XMMS2.
  • AAC in MP4 encoded with iTunes 7.0 can be gapless with iTunes 7.0 and latest foobar2000.

Lossless data compression is a class of data compression algorithms that allows the exact original data to be reconstructed from the compressed data. ... A lossy data compression method is one where compressing data and then decompressing it retrieves data that may well be different from the original, but is close enough to be useful in some way. ... Musepack or MPC is an open source lossy audio codec, specifically optimized for transparent compression of stereo audio at bitrates of 160-180 kbit/s. ... This article is about the audio compression codec. ... Speex is a free software speech codec that claims to be unencumbered by patent restrictions. ... Windows Media Audio (WMA) is a proprietary compressed audio file format developed by Microsoft. ... Look up lame in Wiktionary, the free dictionary. ... Advanced Audio Coding (AAC) is a standardized, lossy compression and encoding scheme for digital audio. ... MPEG-4 Part 14, formally, ISO/IEC 14496-14:2003, is a multimedia container format standard specified as a part of MPEG-4. ... Nero AG is a German software company based in Karlsbad, Germany. ... foobar2000 is a freeware audio player for Windows developed by Peter Pawlowski, a former freelance contractor for Nullsoft. ... XMMS2 (Cross platform music multiplexing system) is a new generation of the XMMS audio player. ... The correct title of this article is . ...

Gapless solutions

• Optimal solutions:
  • Rio Karma and Trekstor Vibez: Gapless hardware players with no software dependency
  • iTunes 7.0 and later versions support gapless playback on Macintosh and Windows without having to combine tracks during encoding (a limitation of previous releases).
  • 2nd generation iPod nano and all video-capable iPods running the latest firmware support gapless playback.
  • Billy 1.03: - A very small resource light mp3 gapless player
  • foobar2000: Gapless playback
  • MiniDisc: Gapless playback
  • Rockbox for various digital audio players.
  • Aqualung, a GNU/Linux audio player specifically designed for gapless playback
  • Music Player Daemon for Linux and other platforms.
• Alternative or partial solutions:
  • Amarok for Linux^[3]
  • MP3Splice: A gapless plugin for Winamp
  • Gapless Winamp output without the use of a plugin: A partial solution for file buffering.
  • Otachan's in_!mpg123: A gapless MP3 decoder for Winamp
  • Winamp 5.2: This version of Winamp features a gapless MP3 decoder. The Vorbis decoder is also gapless.
  • Windows Media Player: Has supported gapless ripping and playback of WMA since Windows Media 9. Available on all current Windows machines.

The Karma is a digital audio player made by Rio. ... The Trekstor Vibez is a Digital Audio Player due to be released in November 2006. ... The correct title of this article is . ... The first Macintosh computer, introduced in 1984, upgraded to a 512K Fat Mac The Macintosh, or Mac, is a line of personal computers designed, developed, manufactured, and marketed by Apple. ... Microsoft Windows is the name of several families of proprietary software operating systems by Microsoft. ... foobar2000 is a freeware audio player for Windows developed by Peter Pawlowski, a former freelance contractor for Nullsoft. ... See also IBMs VM operating system family, where minidisk refers to a logical unit of storage. ... Rockbox is a free software replacement firmware for digital audio players (DAPs). ... Apple iPod, the most popular hard drive-based digital audio player An embedded hard drive-based player (Creative Zen Vision:M), one of the many alternatives for the iPod An MP3 CD player (Philips Expanium) Some mobile phones can be used as digital audio players, such as the Nokia 6233. ... Unix systems filiation. ... Music Player Daemon (MPD) is a music player which allows for remote access from another computer. ... Linux (IPA pronunciation: ) is a Unix-like computer operating system family that uses the Linux kernel. ... Amarok (formerly known as amaroK) is a free software music player for GNU/Linux and other varieties of Unix. ... Linux (IPA pronunciation: ) is a Unix-like computer operating system family that uses the Linux kernel. ... MPEG-1 Audio Layer 3, more commonly referred to as MP3, is a popular digital audio encoding and lossy compression format and algorithm, designed to greatly reduce the amount of data required to represent audio, yet still sound like a faithful reproduction of the original uncompressed audio to most listeners. ... Winamp is a multimedia player made by Nullsoft. ... Winamp is a multimedia player made by Nullsoft. ... Windows Media Player (WMP) is a digital media player and media library application developed by Microsoft that is used for playing audio, video and images on personal computers running the Microsoft Windows operating system, as well as on Pocket PC and Windows Mobile-based devices. ...

See also

• Ogg Vorbis

This page is about the audio compression codec. ...

References

1. ^ Taylor, Mark (2003). LAME Technical FAQ. Retrieved on 2006-07-06.
2. ^ Robinson, David (2001). lame v3.81 and 3.87 beta mp3 decoding quality test results. Retrieved on 2006-08-24. Features a table of encoder delay values.
3. ^ Thread on Gapless Playback on Amarok Mailing List (2006-09-06). Retrieved on 2007-01-19.

For the Manfred Mann album, see 2006 (album). ... July 6 is the 187th day of the year (188th in leap years) in the Gregorian Calendar, with 178 days remaining. ... For the Manfred Mann album, see 2006 (album). ... August 24 is the 236th day of the year in the Gregorian Calendar (237th in leap years), with 129 days remaining. ... 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the Anno Domini (common) era. ... January 19 is the 19th day of the year in the Gregorian calendar. ...

External link

• MP3 players: Buyer Beware, a description of gapless playback in digital audio players