A Unified Transient Detector for Enhanced aacPlus Encoder
Enhanced aacPlus audio codec is a combination of MPEG-4 Advanced Audio Coding (AAC), Spectral Band Replication (SBR) and Parametric Stereo (PS). To deal with transient signal, SBR and AAC employ separate transient detectors, although both detectors basically perform detection on the same signal. This paper presents an idea of a low-complexity transient detector which operates in PS encoder. It performs online detection at the same time as PS spatial parameter extraction and takes advantage of some computations performed for subband grouping. Testing on a few percussive solo instrument signals and percussive mixture shows good transient information matching with the transient information generated by the original SBR and AAC detectors, with much less computational requirements. This implies that complexity of the encoder can be reduced by replacing both detectors with the proposed unified low-complexity detector.
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