Qdmc2

QDesign Music A quick analysis by Benjamin Larsson e-mail: banan@student.luth.se Version 1.2 14th January 2004 Contents 1 Abstract 3 2 Introduction 3 3 Test of QDM2 3 4 Assumptions 3 5 Facts 7 5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.2 Blocktable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.3 Packet table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.4 Bitstream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.4.1 Checksum calculation routine . . . . . . . . . . . . . . . . 8 5.4.2 Structure decoding . . . . . . . . . . . . . . . . . . . . . . 9 5.4.3 Bitstream terminator . . . . . . . . . . . . . . . . . . . . 9 5.5 Sound resynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5.6 Decoding procedure . . . . . . . . . . . . . . . . . . . . . . . . . 9 6 Further Progress 10 7 Comments 10 8 Version History 10 9 References 10 10 Hexdump of packets 10 10.1 11025 Hz 24 kbit mono white noise . . . . . . . . . . . . . . . . . 11 10.2 11025 Hz 24 kbit mono silence . . . . . . . . . . . . . . . . . . . 11 2 1 Abstract This is an initial analysis of QDesigns audiocodecs QDMC and QDM2 (QDM aka QDesign Music). The goal is to eventually understand the structure of the codecs and finally be able to decode it. 2 Introduction QDMC is an audio compression-codec from QDesign. It is mainly used in Quick- time [2] from Apple. So far very little is(was) known about this codec. It seams to originally come from Dmitry Shmunk’s LB codec. (Low bitrate codec). He was abit active on usenet 96-97, he made the LBpack/LBplay media player. From the history in one of the version of his mediaplayer [4], there is a note of using a Radix-4 FFT implementaion in the player. No other useful information could be found about the technique used for the codec. The only other source of information seams to be from QDesign themself from their pressreleases [1]. The only valuable information from those is that QDMC is a perceptual co- dec. That indicating a propritary psycoacoustics implementation. Although the pressrelease for QDMC says it is fundamentally different f…