An encoding method that permanently removes audio data deemed perceptually inaudible in order to produce a smaller file.
Lossy compression encodes audio by analyzing the signal with a psychoacoustic model and discarding frequency content that human hearing is unlikely to detect, such as sounds masked by louder simultaneous frequencies. The resulting file is a fraction of the size of the original but cannot be decoded back to the exact original waveform because the removed data is gone permanently.
Why it matters
MP3, AAC, and OGG files that DJs purchase or download from streaming services are all lossy-compressed. At high bitrates (320 kbps MP3 or 256 kbps AAC) the quality loss is negligible for most playback systems, but at lower bitrates (128 kbps or below) artefacts such as smearing, pre-ringing on transients, and high-frequency distortion can be audible on club-grade PA systems. Knowing the bitrate and format of a file helps a DJ decide whether it is suitable for a particular context.
