In digital recording and audio coding, a pre-echo is a disturbance in the audio signal caused by the encoder , which becomes audible before the triggering acoustic event.
In digital recording, the audio signal is encoded in blocks (in time windows). The in coding resulting quantization noise is spread over the entire time window. The quantization noise is audible in front of the audio signal, which is supposed to mask the noise.
The copying effect generates both pre-echoes and post-echoes, especially with analogue tapes, whereby the pre-echo is more disturbing. The post-echo is often masked by the main signal.