How does it work?

Using methods derived from our work on instrumentation for particle physics we have investigated the problem of audio reconstruction from mechanical recordings. The idea was to acquire digital maps of the surface of the media, without contact, and then apply image analysis methods to recover the audio data and reduce noise. This work has been described in two papers which have been published in the Journal of the Audio Engineering Society: Journal of Audio Engineering Society, Vol. 51, No. 12, pp.1172-1185 (2003 Dec.), and Journal of Audio Engineering Society, Vol. 53, no.6, pp.485-508 (2005 June).

The preservation challenge for mechanical recording media revolves around its fragility and pre-existing wear or damage. The access challenge is to find an efficient way to massively transfer hundreds of thousands of discs, or other media, to digital form. Both these challenges can be addressed by applying non-contact optical technologies and data analysis methods to the digitization and restoration of historical recordings. Optical methods protect the samples from further damage and can circumvent many aspects of pre-existing damage. These methods are readily automated and allow the offloading of many aspects of the transfer process to software. This can represent a viable mass digitization strategy.

The basic idea of the optical approach is to create a high resolution digital map of the surface of the sound carrier (disc record, wax cylinder, etc.). Given this map, image processing methods can be applied to overcome the effects of wear or damage, and the stylus motion can be digitally emulated. By calculating the motion of a virtual stylus moving through the map the audio content can be reproduced.

The IRENE technology makes use of the following methods, some of which are also evolving dramatically, as they are important for many other applications, both commercial and academic.

  • Electronic Imaging:the use of photo-sensitive electronic sensors to acquire images and make them available to a digital computer.
  • Image and Signal Processing: the use of computers to mathematically analyze and alter images and waveforms represented in digital form.
  • Optical Metrology: the use of electronic imaging, image processing, and precision motion control to derive quantitative information about the size and shape of physical objects.
  • Machine Vision: a set of processes utilizing electronic imaging, processing, and metrology methods to recognize, classify, and analyze the geometry of real objects.

The advantages and key attributes of the optical recovery process can be summarized as follows:

  • Delicate samples can be played without further damage.
  • Effects of damage and debris (noise sources) can be reduced through image processing since they can be objectively recognized as not matching the known shape of the groove. Thus, these discrete noise sources are resolved in the “spatial domain” where they originate and need not be considered as random effects in an audio waveform.
  • Scratched regions can be interpolated.
  • Dynamic effects of damage (skips, ringing) are absent.
  • The method is largely independent of record material and format – wax, metal, shellac, lacquer etc. can be measured with the same procedures.
  • Classic distortions and systematic errors (wow, flutter, tracing and tracking errors, pinch effects etc.) are absent or removed as geometrical corrections.
  • No mechanical method is needed to follow the groove.
  • Certain broken samples can re-assembled and played back.
  • The acquired image data can be used to analyze the physical condition and characteristics of the sample such as groove width, defect rate, and other statistical quantities.
  • Optically scanned data can be analyzed and archived as simple digital sound files (.wav etc) just as in any normal audio transfer process. In addition, the high resolution digital images can be archived as standard image data (TIFF etc) for future re-analysis. No special formats or media are required.

Dr. Carl Haber, Senior Physicist
Lawrence Berkeley National Laboratory

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Want to know more?

University of California at Berkeley Library Online Exhibition entitled “Project IRENE” is a wonderful way to understand more about IRENE technology!