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MPEG-4 AUDIO OVERVIEW

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MPEG-4 AUDIO OVERVIEW

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  1. MPEG-4 AUDIO OVERVIEW Roberta Eklund Consultant

  2. MPEG-4 Audio Overview • Natural Audio • T/F • CELP • PARA • Structured Audio • SAOL • SASL • SASBF • MIDI-DLS-version 2 • TTS • Cross Tool(Algorithm) Functionality • Pitch/tempo change • Bitrate scalability • Computation complexity scalability • Error robustness • Audio related effects • Acoustic virtualization

  3. Different Tools for Bitrates/Application

  4. MPEG-4 Audio Tools PROFILES • Object Profile - defines the syntax of the bitstream for one single Object, that can represent a meaningful entity in the Audio or Visual scene. Elementary bitstream • Composition Profile - defines which different Object Profiles can be combined in the Audio or Visual scene. Combinations of Elementary bitstreams.

  5. OBJECT PROFILES

  6. Combination Profiles

  7. MPEG-4 Encoder Structure

  8. MPEG-4 T/FEncoderConfiguration

  9. MPEG-4 T/F DecoderConfiguration

  10. Block Diagram of CELP Encoder

  11. Block Diagram of CELP Decoder • Excitation signal generator: • codebook • regular pulse excitation (RPE) • multi-pulse excitation (MPE)

  12. Block Diagram of PARA Encoder

  13. Block Diagram of PARA Decoder

  14. PARA is Two Codecs in One Two operating modes • harmonic and noise components (HVXC) • for speech coding at 2...4 kbps • harm. & indiv. sinusoidal comp. + noise (HILN) • for coding of music signals with low complexity content (e.g. single instruments) at 4...16 kbps • combination of both modes • support by syntax, defined transition • automatic mode selector • cross fade from one signal to another one

  15. Text-to-Speech • Phonemic (language-independent) syntax • Prosody, timing cues • Language, dialect, gender, age parameters • Automatic synchronization with FBA • Exact TTS synthesis non-normative; only interface is specified

  16. Structured Audio • Structured Audio - Sound coding using structured descriptions • Structured Audio decoder - music and sound-effect synthesis • MMA, Microsoft, EMU now collaborating on MIDI DLS-version 2 in MPEG4

  17. SAOL • Downloadable BNF synthesis grammar • Header contains description of several synthesizers and effects processors control algorithms and routing instructions for audio flow of control • SAOL has 100 primitive processing instructions, signal generators and operators which fill wavetables with data.

  18. SASL and MIDI • New format for describing control parameters - Basically a scheduler of audio events - Designed to interface well with SAOL - New Control Language Similar to MIDI • MIDI (Musical Instrument Digital Interface) • Simpler format for describing control • Included as alternate control method • Leverages existing authoring tools • Gives “backwards compatibility” to SA

  19. DLS Level 2 • Aims at consistent synthetic audio playback across wide range of platforms • Defines a simple wavetable synthesizer • Bitstream includes sound samples • Score expressed in MIDI • Growing support from both software and hardware developers • DLS Part of DirectMusic in Microsoft’s DirectX 6.0

  20. DLS-2 synthesizer model • Simple yet powerful structure much alike to many existing synthesizers in the market (eg in PC soundcards) • Uses loopable samples as sound sources (wavetable) • variable routing of control sources • 2 envelopes for amplitude control • 2 low frequency oscillators • 1-pole dynamic low-pass filter • Standardized response to MIDI controllers

  21. Audio Bifs Synchronization with Visual! BIFSstuff AudioMix AudioMix HRTF AudioFX AudioFX AudioFX AudioDelay AudioSource AudioSource AudioSource Finger snaps (Parametric) Bass (SA) Piano (SA) Audiochannels

  22. Demo Audio BIFS

  23. Conclusion • MPEG-4 Audio attempts to offer solutions to all spectra of sound. • Some of the tools are more stable, while others are still in Research and Development. • MPEG2-AAC is the best multi-channel lossy audio compression standard to date.

  24. Acknowledgements I would like to thank the authors from the references for providing the material presented here today.

  25. Definitions • T/F Time/Frequency (MDCT transform) • AAC Advanced Audio Coding • PARA Parametric • CELP Code Excited Linear Prediction • SA Structured Audio • PNS Perceptual Noise Substitution • HVXC Harmonic Vector eXcitation Coding • HILN Harmonic and Individual Line + Noise • SAOL Structured Audio Orchestra Language • SASL Structured Audio Score Language • MIDI Musical Instrument Digital Interface • TTS Text to Speech

  26. More Definitions • CD Committee Draft • IS13818-7 Advanced Audio Coding • LC Low Complexity • BSAC Bit Sliced Arithmetic Coding • SSR Scalable Sample Rate • PNS Perceptual Noise Substitution • VBR Variable Bit Rate • TLSS Tools for Large Step Scalability • SNHC Synthetic/Natural Hybrid Coding • DLS Downloadable Samples

  27. Natural Audio Complexity

  28. AAC Decoder ComplexityEvaluation MPEG AAC Decoder Complexity 2-channel Main Profile 40% of 133 MHz Pentium 2-channel Low Complexity 25% of 133 MHz Pentium 5-channel Main Profile 90 sq. mm die, 0.5 micron CMOS 5-channel Low Complexity 60 sq.mm die, 0.5 micron CMOS

  29. AAC Test Results • Test at BBC and NHK according to ITU-R BS.1116 • triple-stimulus/hidden-reference/double-blind • ITU-R 5-point impairment scale • 95% Confidence Intervals • MPEG AAC provides “indistinguishable” quality at 320 kb/s per five channels • MPEG AAC at 320 kb/s outperforms MPEG BC Layer II at 640 kb/s per five channels • Recent Stereo Tests at NHK Showed MPEG AAC provides “indistinguishable” quality at 128 kb/s per two channels

  30. References • M. Bosi, E. Schrierer, B. Edler, Peter G. Schreiner MPEG-4 Seminar, Fribourg, Switzerland 1997 • S. Quackenbush, “Coding of Natural Audio in MPEG-4”, Proc IEEE ICASSP, Seattle, 1998 • B. Grill, B. Edler, I. Kaneko, Y. Lee, M. Nishiguichi, E. Scheirer, and M. Väänänen (Eds). ISO 14496-4(MPEG-4 Audio) Committee Draft. MPEG document N1903 • E. Schrier, “The MPEG-4 Structured Audio Standard”, Proc IEEE ICASSP, Seattle, 1998 • Juergen Herre, “Updated Description for Perceptual Noise Substitution Tool”, MPEG Document M2692 • E. Scheirer, R. Väänänen, J. Huopaniemi, “AudioBIFS: The MPEG-4 Standard for Effects Processing”, AES, SF, 1998 • Overview: http://www.cselt.it/mpeg/standards/mpeg-4/mpeg-4.htm