Audio Transmission

Abstract

Audio with good quality is the essential fundament for all multi-media services. The transmission of audio signals relies on efficient encoding and decoding algorithms (codecs) that enable the reduction of the required channel capacity, but still provide an excellent audio quality, even when transmission errors occur. The most succesfull audio codecs are mp2, mp3, aac and ac3. The codecs employ sophisticated signal processing algorithms imitating properties of hearing. The processing may cause specific artifacts such as high frequency loss, narrow-band noise and pre-echoes. The final quality needs to be verified with statistically valid listening tests. Detailed procedures for conducting reliable speech and audio tests are defined in ITU Recommendations P.800, BS.1116, and BS.1534. Instrumental measurement methods such as BS.1387 replicate subjective tests allowing the estimation of the perceived quality. The ITU Recommendation P.1201 is a recently standardized method for estimating the audio quality of a transmitted signal without the need to have a reference signal available.