Flexible Audio Coder

Abstract: As modern communications networks are heterogeneous and, therefore, highly variable, the design of source coders should reflect this network variability. It is desired that source coders are able to adapt instantly to any bit-rate constraint. Source coders that possess this property offer coding flexibility that facilitates optimal utilization of the available communication channel within a heterogeneous network. Flexible coders are able to utilize feedback information and therefore perform an instant re-optimization. This property implies that flexible audio coders are better suited for networks with high variability due to the fact a single configuration of the flexible coder can operate at continuum of bit-rates. The aim of the thesis is to implement a flexible audio coder in a real-time demonstrator (VoIP application) that facilitates instant re-optimization of the flexible coding scheme. The demonstrator provides real-time full-duplex communications over a packet network and the operating bit-rate may be adjusted on the fly. The coding performance of the flexible audio coding scheme should remain comparable to non-flexible schemes optimized at their operating bitrates. The report provides a background for the thesis work and describes the real-time implementation of the demonstrator. Finally, test results are provided. The coder is evaluated by means of a subjective MUSHRA test. The performance of the flexible audio coder is compared to relevant state-of-the-art codecs.