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In some cases, software closes and re-opens the output stream when switching tracks, causing the hardware to create a very short "click". Poorly designed playback systems Įven when the audio file itself does not contain undesirable gaps, software/firmware/hardware design often adds gaps during playback. More recent (newer than MP3) compressed audio formats have been designed to address this problem, and can therefore produce gapless audio if played back correctly. Some encoders use a nonstandard header to store actual encoder delay & padding values, but not all players/decoders support it. Encoder delay may vary from encoder to encoder, making automatic removal difficult. The popular MP3 standard, for example, defines no way to record the amount of delay or padding for later removal. This issue is technical but also standards-related. Likewise, if the decoder delay is not accounted for, the gap at the end will be further enlarged. ![]() If the amount of encoder delay and padding are not all accurately accounted for, the encoded silence will be decoded together with the audio data, creating gaps at the ends of the track. This makes the overall padding amount hard to predict, if the length of the input isn't known. In order to fill up the last block, silence may be appended to the input before the transform. Yet another factor is the fact that transforms act on data in units of fixed-size blocks. The encoder may add a consistent number of silent samples to one or both ends to achieve this. Therefore, a little bit of extra signal is required at both ends of the input in order to fully and accurately encode the frequencies found in the original ends. This gap can be enlarged at decode time when a reverse-MDCT is performed, because the reverse transform will also introduce a gap (decoder delay) of its own.Īnother part of the encoder delay and padding is related to the overlapping nature of MDCT transforms each segment of the encoded audio depends in part on adjacent segments. ![]() Many compression schemes involve a time/frequency domain transform (such as an MDCT) which unavoidably introduces a certain amount of silence (part of the encoder delay) at the beginning of the stream. Common encoder delay values are in a table below. Padding normally is only added by the encoder. Delay can be called encoder delay or decoder delay depending on what part of the compression scheme introduces the delay. Silence at the beginning is called delay and silence at the end is padding. Due to the introduction of such gaps, the duration of the output is slightly increased. Most lossy audio compression schemes add a small amount of silence to both ends of the audio. There are two main reasons why gaps occur during playback: compression scheme artifacts and poorly designed playback systems. Upon playback, a click or a brief (fraction-of-a-second) pause can be heard between tracks.Įven if two lossily-compressed tracks are decompressed and merged into a single track, a gap will usually remain between them.During or after the creation of the files, the audio data is compressed with a lossy codec like MP3.Someone uses DAE software to extract audio data from an audio CD and save it to separate files, one for each track. PORTABLE LOSSLESS MUSIC PLAYERS WITH GAPLESS PLAYBACK HOW TO6 How to add or repair gap metadata in MP3s.
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