How Lossy Compression Works
Lossy codecs exploit psychoacoustics: quiet sounds masked by louder ones, frequencies at the edge of hearing, and stereo detail the brain does not resolve are all candidates for removal. The encoder allocates its limited bitrate budget to what matters perceptually. At generous bitrates (256-320 kbps MP3) the result is usually indistinguishable from the source; at low bitrates you hear artifacts - smeared highs, warbling, and a general dullness.
How Lossless Compression Works
Lossless codecs like FLAC and ALAC work like ZIP for sound: they find statistical redundancy and encode it more compactly, typically reaching 50-70% of the original size. Decoding returns the exact original samples. Uncompressed formats such as WAV and AIFF are also lossless - they simply skip the compression step entirely.
The Golden Rule: Loss Is One-Way
Converting lossless to lossy discards data forever. Converting lossy back to lossless (an MP3 to a WAV, say) produces a bigger file with exactly the same missing data - nothing is recovered. Equally important, each lossy-to-lossy conversion adds fresh loss, so avoid repeated MP3 re-encodes. The practical workflow: record and edit in lossless, archive in FLAC, and export lossy copies for distribution as the final step.
Which Should You Use Day to Day?
- Casual listening, phones, sharing: lossy (MP3 at 256-320 kbps) - the quality is excellent and files are small.
- Archiving masters, DJ libraries, audiophile playback: lossless (FLAC).
- Editing and production: WAV or AIFF, then export.
When you need to move between camps, mp3.now handles it: FLAC to MP3 and WAV to MP3 for shrinking, MP3 to WAV when a tool demands lossless input. Upload, choose options, hit Convert, download - with batches of up to 10 files supported.
How to Tell What You Have
The file extension is the first clue: .mp3, .aac, .ogg, and .opus are always lossy; .wav, .flac, .aiff, and .ape are lossless. The ambiguous one is .m4a, which holds either lossy AAC or lossless ALAC - check the codec in your player's file-info panel. Bitrate is the second clue: lossless stereo music typically shows 700-1,100 kbps, while lossy files top out at 320 kbps. One trap to know about: a FLAC file created from an MP3 is technically lossless from that point on, but the MP3's losses are baked in forever - the file is no better than its worst ancestor. This is why provenance matters when someone offers you a lossless copy, and why you should note where your own archives originally came from.