1. A method for optimizing performance of Advanced Audio Coding of an audio source sequence, the Advanced Audio Coding being dependent on a quantized spectral coefficient sequence, wherein the quantized spectral coefficient sequence is a quantized sequence of the audio source sequence, the method comprising: determining values of the quantized spectral coefficient sequence which minimize a cost function of an encoding of the audio source sequence within a predetermined threshold, by using soft decision quantization, the cost function being dependent on the quantized spectral coefficient sequence; and performing Advanced Audio Coding of the audio source sequence using the determined quantized spectral coefficient sequence.