INTERNATIONAL ORGANISATION FOR STANDARDISATION
ORGANISATION INTERNATIONALE DE NORMALISATION
ISO/IEC JTC1/SC29/WG11
CODING OF MOVING PICTURES AND
AUDIO
ISO/IEC JTC1/SC29/WG11
N7706
MPEG2005/
October 2005, Nice, FR
Source: Audio Subgroup
Status: Approved
Title: MPEG Technologies:
Audio Lossless Coding
Author: T. Liebchen
Audio Lossless Coding (ALS) is a lossless audio coding algorithm that provides state of the art lossless compression for audio signals.
ALS offers flexibility in terms of compression-complexity tradeoff, ranging from very low-complexity implementations to maximum compression modes, thus adapting to different requirements.
The ALS standardization effort was focused on providing a highly efficient and fast lossless audio compression scheme for both professional and consumer applications.
It is anticipated that a global standard will facilitate interoperability between different hardware and software platforms, thus promoting long-lasting multivendor support.
The basic ALS algorithm essentially uses forward-adaptive linear predictive coding (LPC). The prediction residual is transmitted along with quantized filter coefficients. The decoder applies the inverse prediction filter in order to achieve lossless reconstruction. The following figure shows a block diagram of the basic ALS encoder.
Additional tools, which can be switched on to improve compression, comprise long-term prediction (LTP) and multi-channel prediction (MCC). Alternatively, a backward-adaptive predictor (RLS-LMS) can be used instead of the forward-adaptive predictor.
ALS is aimed at applications that require unimpaired quality at reduced data rates, including audio compression in studio operations, preservation and archival systems, as well as delivery by physical media and over computer networks.