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Pre-echo
From Wikipedia, the free encyclopedia
Pre-echo is a psychoacoustic phenomenon where an unusually noticeable artifact is heard in a sound recording from the energy of time domain transients smeared backwards in time after processing in the frequency domain due to the Gibbs phenomenon. Because forward temporal masking is so much stronger than backwards temporal masking, the Gibbs phenomenon can give rise to this audible distortion which sounds like an echo which comes before the actual sound.
In an effort to avoid pre-echo artifacts, many sound processing systems use filters where all of the response occurs after the main impulse, rather than linear phase filters. Such filters necessarily introduce phase distortion and temporal smearing, but this additional distortion is less audible because of strong forward masking.
Avoiding pre-echo is a substantial design difficulty in transform domain lossy audio codecs such as MP3, MPEG-4 AAC, and Vorbis.