A problem of audio source coding systems is the quantizing noise, which appears even shortly before the beginning of the audio signal. This is caused by the frequency analysis, which is performed in these coders to locate the quantizing noise below the masking pattern. The masking of preceding noise, the so-called premasking effect in the human ear, tolerates only very small levels within a few milliseconds. In this paper, a method is shown to decrease the preceding quantizing noise below audibility of preprocessing the signal when sharp attacks occur, where the noise normally is not always completely masked by the human ear, especially, when low data rates are needed for source coding. In these cases, the level of the signal becomes modified before source coding, and a small side information is provided for the decoder to restore the original level flow behind the source decoder.
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