Digital Audio Restoration
Simon Godsill
Signal Processing Group
University of Cambridge
www-sigproc.eng.cam.ac.uk/~sjg
Overview
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Audio Restoration - motivation
Audio Restoration in Cambridge 1984-2003
Review of core technologies
Audio restoration - principles
Advanced topics
Emerging techniques
Audio Restoration - motivation
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Requirement to enhance material from
– Sound Archives:
– Historical disk remastering:
– `Recent’ Magnetic Tape recordings:
– Forensic recordings, …
Audio Restoration in Cambridge
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1984-88 - British Library funds research into restoration of archived
gramophone recordings at Signal Processing Group with Prof. Peter
Rayner.
1988 Cambridge company spun-out: CEDAR Audio. First real-time dehiss 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
De-click, de-crackle
 De-hiss
 Resonant noise pulse removal
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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
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De-hiss
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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)
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* Courtesy Patrick Wolfe – see
www-sigproc.eng.cam.ac.uk/~pjw47
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
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Low frequency noise pulse removal, contd.
Advanced Topics
Bayesian statistical models
 De-clipping/de-quantizing
 Pitch variation defects (Wow)
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Future Directions
Resources
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`Digital Audio Restoration - a statistical
model-based approach’ by Simon
Godsill and Peter Rayner, SpringerVerlag 1998
 See www-sigproc.eng.cam.ac.uk/~sjg
for extracts, publications and sound
examples