FLAC, MP3, OGG and the rest: what the format means on air

Music turns up in a handful of formats, and which one you want depends less on audiophile argument and more on what you plan to do with the file.

The formats you will actually meet

• FLAC. Lossless compression, typically 700kbps and up. Bit for bit identical to the source once decoded. Roughly three to five times the size of a good MP3.
• MP3. Lossy, universally supported, and still the most common thing in any catalog. At 320kbps it is transparent enough for nearly every listener.
• M4A and AAC. Lossy, more efficient than MP3 at the same bitrate, common on anything sourced from a store.
• OGG and Opus. Lossy, technically excellent, especially at low bitrates. Less common in older catalogs.
• WAV. Uncompressed. Enormous, no tags worth the name, and rarely what you want from an index.
• APE and WavPack. Lossless, rarer, and not supported everywhere.

Why lossless is not automatically right for broadcast

A radio station does not play files at their source quality. It encodes a stream, usually somewhere between 64 and 192kbps. Everything you send is re-encoded before a listener hears it.

That matters because of generation loss. Encoding lossy audio a second time compounds the artefacts of the first pass, since the encoder cannot tell which detail was already discarded. So:

• FLAC into your encoder is genuinely better, because the encoder starts from the original signal.
• A 320kbps MP3 is fine for almost any stream bitrate you will actually broadcast at.
• A 128kbps MP3 is the one to avoid, especially at higher stream bitrates, where you are faithfully transmitting the artefacts of a bad rip.

The practical rule

Set a floor, not a preference. Ask for lossless where it exists, accept 320kbps MP3 where it does not, and reject anything below about 192kbps unless nothing else carries the song. An index that records the format and bitrate of every entry lets you enforce that as a filter instead of a hope.

The one place to relax the rule is rarity. For a track that exists exactly once, in one poor rip, a listenable 128kbps copy beats silence. Quality floors should have an exception for scarcity, because the alternative is a station that cannot play the songs nobody else has either.