Analysis of Decompressed Audio-The -Inverse Decoder-
Perceptual audio coding has become a widely used technique for economic transmission and storage of high-quality audio signals. For the reproduction of compressed audio, the bitstream is expanded into a standard audio format, such as linear PCM, by the decoding algorithm. This paper investigates the questions: Is it possible to recover the compression parameters from an analysis of the decoded audio signal? Can a decoded audio signal be translated back into its bitstream representation (the -inverse decoding- problem)? An algorithmic approach to these questions is presented and detailed based on the MPEG-2/4 AAC coder. Several interesting applications for such techniques are discussed, including identification of the used coding algorithm and tandem-resistant re-encoding of audio signals.:
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