Real-time ultra-low delay audio coding for wireless transmission

Encoding and decoding delays have become increasingly critical in real-time audio wireless applications. In order to maximize compression and minimize coding delays, this paper presents a two dimensional (2D) fast lifting wavelet technique with boundary effects minimized for very short block processing to achieve ultra low delay for wireless transmission. The 2D spatial-frequency processing of audio input signal fully exploits the correlation for better compression performance. A modified 2D embedded 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 embedded coding offers the error resilience feature that is evaluated using a simulated transmission channel with random errors. In the face of transmission errors, joint source-channel SPIHT coding scheme for unequal error protection thus can be easily designed by varying both source coding bit rate and channel coding redundancy with added complexity and delay depending on the channel error degree. Experimental tests demonstrate that the proposed coder is efficient and has low complexity with less memory requirements in implementation.