2D spatial-frequency processing based audio coding for real time wireless transmission

Wireless systems are often subject to bandwidth or cost constraints which are incompatible with high data rates. The key enabling technology for digital audio wireless products is data compression. For real time wireless transmission, very low encoding and decoding delay has become an essential prerequisite. In live productions, the tolerable total delay time is less than a few milliseconds. Current audio coding schemes like MPEG standards or wavelet techniques can hardly reach such a threshold by using overlapping frames of input signal with psychoacoustic model. This paper presents a two dimensional (2D) spatial-frequency processing based audio coder with ultra low delay for real time wireless applications using non-overlapping short block processing and embedded coding. 2D fast lifting wavelet transform with boundary effects minimized is developed for further exploring the correlation of the audio signal. A modified 2D SPIHT (set partitioning in hierarchical trees) algorithm with more bits used to encode the wavelet coefficients and transmitting fewer bits in the sorting pass, is implemented to reduce the correlation between the coefficients at different decomposition levels and inside each band at scalable bit rates. The experiment shows the proposed coder is efficient and has low complexity with less memory requirements in implementation.