Streaming over the Internet with a scalable parametric audio coder

Audio compression has progressively gained higher importance in the Internet thanks to massive amount of multimedia services on it. This new services require coders adapted to that new environment. Therefore, new generation coders use more complex models focused on features which make possible its use for audio streaming over the Internet, mainly low bit rate, scalability and robustness. In our case, a good trade-off between bit rate reduction and audio quality is achieved by using parametric audio coding, and furthermore, this coder has a scalable version, optimized for streaming requirements. This coder avoids differential information between coded audio segments and uses a layered scheme for changing straightforwardly the bit rate. The results reveal our coder as a good candidate for massive distributed audio applications, like music on demand, radio broadcasting or real-time streaming audio. In this article are shown the main features of this coder and their implication on streaming.

1. Introduction

The continuous increase of multimedia services and content over the Internet has encouraged, in the last years, the search of low bit rate coders with good quality. Moreover, wireless media access begun to be usual so services have to be available everywhere to a wide number of users. From this can be derived two objectives: low bit rate-good quality coding and streaming oriented. For the first one, a parametric audio coder has been developed, and for the last, scalability has been added. Parametric coding of audio signals has become a popular tool for representing audio signals at very low bit rates [1] [2] [3]. This high level description or model for audio signals can provide a framework to meet the demands of the Internet streaming audio problem and the increase of wireless access through GSM/GPRS and UMTS. The nature of high level signal models allows large compression rates, scalable compression and flexibility, all required for a suitable deployment over the Internet. The coder uses a three components signal model which assumes the signal to be represented as an addition of sines, transients and noise. Then, using psychoacoustic parameters, each component is divided among layers to provide scalability.