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40 MPEG Digital Audio Coding Standards

Typical audio signal classes are telephone speech, wideband speech, and wideband audio, all of which differ in bandwidth, dynamic range, and in listener expectation of offered quality. The quality of telephone-bandwidth speech is acceptable for telephony and for some videotelephony and video-conferencing services. | Peter Noll. MPEG Digital Audio Coding Standards. 2000 CRC Press LLC. http www.engnetbase.com . MPEG Digital Audio Coding Standards Peter Noll Technical University of Berlin 40.1 Introduction 40.2 Key Technologies in Audio Coding Auditory Masking and Perceptual Coding Frequency Domain Coding Window Switching Dynamic Bit Allocation 40.3 MPEG-1 Audio Coding The Basics Layers I and II Layer III Frame and Multiplex Structure Subjective Quality 40.4 MPEG-2 Audio Multichannel Coding MPEG-2 Audio Multichannel Coding Backward-Compatible BC MPEG-2 Audio Coding Advanced MPEG-2 Audio Coding AAC Simulcast Transmission Subjective Tests 40.5 MPEG-4 Audio Coding 40.6 Applications 40.7 Conclusions References 40.1 Introduction PCM Bit Rates Typical audio signal classes are telephone speech wideband speech and wideband audio all of which differ in bandwidth dynamic range and in listener expectation of offered quality. The quality of telephone-bandwidth speech is acceptable for telephony and for some videotelephony and video-conferencing services. Higher bandwidths 7 kHz for wideband speech may be necessary to improve the intelligibility and naturalness of speech. Wideband high fidelity audio representation including multichannel audio needs bandwidths of at least 15 kHz. The conventional digital format for these signals is PCM with sampling rates and amplitude resolutions PCM bits per sample as given in Table 40.1. The compact disc CD is today s de facto standard of digital audio representation. On a CD with its 44.1 kHz sampling rate the resulting stereo net bit rate is 2 x 44.1 x 16 x 1000 1.41 Mb s see Table 40.2 . However the CD needs a significant overhead for a runlength-limited line code which maps 8 information bits into 14 bits for synchronization and for error correction resulting in a 49-bit representation of each 16-bit audio sample. Hence the total stereo bit rate is 1.41 x 49 16 4.32Mb s. Table 40.2 compares bit rates of the compact disc and the digital audio tape DAT .