What is Lossless?

Lossless compression shrinks data in a way that lets the original be rebuilt exactly. Examples include ZIP and 7z archives, PNG images, and FLAC or ALAC audio. Decompress them and you get precisely what went in.

Lossless files are larger than lossy ones. A FLAC album is typically several times the size of the same album as MP3, and a PNG photo is usually much bigger than a JPG.

The word also applies to transfers. A lossless transfer delivers the same bytes you sent, which you can confirm with a checksum. This site delivers files that way.

Uncompressed and lossless are not quite the same. A WAV file is usually not compressed at all. A FLAC file is compressed, but losslessly, so it plays back identical audio from a smaller file.

CD-quality audio is 44,100 samples per second, 16 bits each, in 2 channels: 44,100 × 16 × 2 = 1,411,200 bits per second, about 1,411 kbps.

One minute uncompressed is 1,411,200 × 60 ÷ 8 = about 10.6 MB. FLAC makes this noticeably smaller with no loss at all, by an amount that depends on the music.

For comparison, an MP3 at 320 kbps is 320,000 × 60 ÷ 8 = 2.4 MB per minute, about a quarter of the uncompressed size, but some detail is gone for good.

• Send files through a download link rather than a chat app or social network, which may re-compress them.
• On phones, pick the file itself (for example from the Files app) instead of a preview.
• Compare the SHA-256 checksum shown on the download page with the downloaded file. A match proves every byte arrived.

This matters most for files that will be edited, printed or archived, where hidden loss could show up much later.