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A Robust and Efficient Implementation of MPEG-2/4 AAC Natural Audio Coders

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This paper discusses a new DSP based real-time implementation of the MPEG-2/4 AAC standards using a set of non-optimal solutions to reduce the computational load. These solutions comprise a novel implementation of a MDCT-based psychoacoustic model, managing a birth/death scheme which aims to overcome false power spectrum estimates due to the cosine transform, a smoothing of the scalefactors guided by an estimation of the increment in the quantization noise and a loop-free bit allocation method based on an overestimation of the noise level. These techniques provide both robustness and efficiency to the scheme. Other fixed-point DSP programming considerations required to achieve the real-time implementation, including a choice of a MDCT fast algorithm, are presented.

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