Edasikäiku

Edasikäiku (Finnish for “pre-echo” or “forward echo”) is a term used in acoustics and audio engineering to describe an auditory artifact in which a faint echo is heard before a sudden transient in a sound. In English-language literature the phenomenon is commonly called pre-echo. It is most noticeable in digitally encoded audio where the processing uses block-based time-frequency representations and aggressive temporal masking.

Mechanism and characteristics: A forthcoming transient’s energy can leak into earlier time frames due to windowing and transform coding. When the psychoacoustic model allows some energy to escape masking, a small echo or smear is heard before the main transient. This effect is particularly typical when short analysis blocks are used near sharp onsets, such as percussion or plosive sounds. The result is perceived as a preliminary whisper of sound preceding the loud attack, which can be undesirable in high-fidelity playback.

Mitigation and context: Codec implementations aim to reduce edasikäiku by using adaptive windowing and longer analysis blocks for dynamic passages, improving masking models, and applying post-processing such as dithering or filtering. In practice, edasikäiku is an important consideration in mastering and in the design of perceptual audio codecs. The term is used in Finnish-language acoustics and education as the local label for what English-language literature calls pre-echo.

See also: pre-echo, psychoacoustics, audio compression.