Modified MP3 encoder using complex modified cosine transform
M. Mathew, V. Bhat, S.M. Thomas, Changhoon Yim · 2003
MPEG-1 layer-3, popularly known as MP3, has revolutionized the digital music domain. MP3 makes use of psychoacoustic modeling to achieve compression through the removal of perceptually irrelevant components of digital audio. The psychoacoustic model is the key element of perceptual coding and requires intensive FFT computation for calculating the frequency spectrum. This spectrum is used to compute masking thresholds. Thus, the original MP3 algorithm computes modified discrete cosine transform (MDCT) and FFT parallelly. The proposed algorithm is an alternative to this. We make use of complex modified discrete cosine transform (CMDCT) of the filter-bank outputs for generating MDCT coefficients as well as the frequency spectrum. This method requires fewer computations than the original method. A novel method of window switching, based on filter-bank output is used to simplify the overall algorithm. The proposed algorithm reduces the amount of computations for MP3 encoder while retaining the audio quality.