Design Article
Algorithmic delay and synchronization in MPEG audio codecs
Ranjani H G and Ameet Kalagi, Ittiam Systems Pvt Ltd
5/5/2010 2:00 PM EDT
Summary
The knowledge of delay encountered while transmitting audio data is key to designing time critical systems. We have the algorithmic delay encountered in MPEG audio codecs and looked at the modules which contribute to this delay. We have also looked at how to synchronize the parametric coding tools to the core waveform coding algorithms. Table 1 summarizes the algorithmic delay in various codecs discussed.
We observe that achieving a good quality at lower bit rates comes at the cost of delay parameter as in AAC-LC and AAC-LD. AAC-LD being the least delay codec is suited for telephony and conferencing applications while codecs like HE-AAC and MPEG Surround are suited for broadcast and streaming applications due to the advantage they offer in terms of bit rate and audio quality.
The delays of the popular audio codecs are derived, thus serving as a ready reference for designs needing A/V sync, in transcoder applications for broadcast space, conferencing and for other real-time systems which have a delay budget.
References:
1. Lutzky M, G Schuller, et al, "A Guideline to Audio Codec Delay", AES 116th convention, May 2004.
2. M. Bosi and R.E. Goldberg, Introduction to digital audio coding and standards, Kluwer Academic Publishers, Boston, 2003.
3. E. Allamanche, R. Geiger, J. Herre and T. Sporer, "MPEG-4 Low Delay Audio Coding Based on the AAC codec", AES 106th convention, Munich, pp. 1-21, May 1999.
4. P.P.Vaidyanathan, Multirate systems and filterbanks, Prentice Hall, Englewood Cliffs, 1993.
5. ISO/IEC MPEG Audio Codec Specifications.
Related links:
Audio Coding: An Introduction to Data Compression - Part 1: Psychoacoustic model, masking, and MPEG Layer I coding | Part 2: MPEG Layer II coding, MP3 and AAC | Part 3: AAC continued, MPEG-4 AAC, Dolby Digital and other standards
Audio coding for wireless applications
A new standard for surround sound
Error-Resilient Coding for Audio Communication - Part 1: Waveform and CELP Speech Codecs | Part 2: Lapped transform codecs | Part 3: FEC techniques for speech and other coding techniques
Low Bit-Rate Audio Coding in Multi-channel Digital Wireless Microphone Systems
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