Digital audio restoration
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Digital Audio Restoration. Simon Godsill Signal Processing Group University of Cambridge www-sigproc.eng.cam.ac.uk/~sjg. Overview. Audio Restoration - motivation Audio Restoration in Cambridge 1984-2003 Review of core technologies Audio restoration - principles Advanced topics

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Digital Audio Restoration

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Digital audio restoration

Digital Audio Restoration

Simon Godsill

Signal Processing Group

University of Cambridge

www-sigproc.eng.cam.ac.uk/~sjg


Overview

Overview

  • Audio Restoration - motivation

  • Audio Restoration in Cambridge 1984-2003

  • Review of core technologies

  • Audio restoration - principles

  • Advanced topics

  • Emerging techniques


Audio restoration motivation

Audio Restoration - motivation

  • Requirement to enhance material from

    • Sound Archives:

    • Historical disk remastering:

    • `Recent’ Magnetic Tape recordings:

    • Forensic recordings, …


Audio restoration in cambridge

Audio Restoration in Cambridge

  • 1984-88 - British Library fundsresearch into restoration of archived gramophone recordings at Signal Processing Group with Prof. Peter Rayner.

  • 1988 Cambridge company spun-out: CEDAR Audio. First real-time de-hiss and de-click in 1990, using DSP hardware on a PC platform.

  • 1990 -- Research into advanced audio processing at Cambridge University - Godsill, Rayner, Wolfe, Fong, …


Core technologies

Core Technologies

  • De-click, de-crackle

  • De-hiss

  • Resonant noise pulse removal


Digital audio restoration

De-click/de-crackle


De click de crackle

De-click/de-crackle

  • Time domain models for clicks and audio

  • Optimal detection and estimation of corrupted samples

  • Use fully Bayesian methods where time permits


De hiss

De-hiss

*

*

  • Frequency-domain methods predominate

  • Non-linear processing of spectral information to incorporate local temporal and frequency dependence

  • Time-domain model-based methods also developed (joint click/hiss removal)

* Courtesy Patrick Wolfe – see

www-sigproc.eng.cam.ac.uk/~pjw47


Resonant noise pulses

Resonant noise pulses

  • Tone-arm resonance in the presence of breakages or other severe damage to gramophone disk grooves

  • Simplest methods subtract an averaged template for the transient

  • More sophisticated methods apply a stochastic model for the resonant system


Digital audio restoration

Low frequency noise pulse removal, contd.


Advanced topics

Advanced Topics

  • Bayesian statistical models

  • De-clipping/de-quantizing

  • Pitch variation defects (Wow)


Future directions

Future Directions


Resources

Resources

  • `Digital Audio Restoration - a statistical model-based approach’ by Simon Godsill and Peter Rayner, Springer-Verlag 1998

  • See www-sigproc.eng.cam.ac.uk/~sjg for extracts, publications and sound examples


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