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Fission's lossless editing

When editing popular formats like MP3 or AAC, most audio editors will cause a loss of sound quality. This occurs because the software repeatedly decodes and re-encodes MP3 and AAC files in order to make changes. To begin editing, they must first decompress the files to its raw audio samples. After editing is complete, the file must be re-encoded back to the lossy MP3 or AAC format. Each re-encoding results in an undesirable reduction in quality.

Unlike other editors, Fission losslessly edits audio files in all of its native formats (MP3, AAC, Apple Lossless, FLAC, AIFF, and WAV).

Packet-Based Editing

To edit losslessly, Fission works by editing a low-level “packet” of the audio file format. That packet is the shortest duration of audio that Fission can edit, and it will vary by file format. The basic formula is as follows:

packet length = packet size ÷ sample rate

For one example, MP3 files have a packet length of 1152. That means a 44.1 kHz MP3 would have packet length of about 0.026 seconds (1152 ÷ 44100). Thus, the smallest part of that file you could select for editing is approximately 2/100ths of a second long. Edits will fall visually along those 0.026 second packets.

In formats like AAC or MP3, audio packets often depend on the contents of other packets. That data can sometimes be removed by edits made in Fission, which may result in a small “blip” or a silence at the editing position. This is inherent to these compressed formats and is unavoidable when editing losslessly.

Audio in lossless formats like AIFF, WAV, and Apple Lossless will not have this issue. Edits will still occur at the packet level for each format, but individual packets are both shorter and self-contained. This enabled more precise cuts, without undesired audio artifacts.