Title: Play it again — Recovering analog audio from degraded tapes using X-ray magnetic dichroism
Speaker:  Dr Sebastian Gliga, Scientist at Paul Scherrer Institute PSI
Moderator: Prof. Susana Cardoso, INESC MN
When: July 18, 2024, 14h30 p.m. @ INESC Lx Auditorium (room #9)

ABSTRACT:
A significant fraction of twentieth century audio-visual heritage is stored on magnetic tape. Between the 1940s and the late 2000s, audio and video recordings were predominantly made on tape. However, magnetic tapes deteriorate over time from wear and chemical degradation. This can prevent their playback using conventional equipment, where the read head is in physical contact with the tensioned tape. Today, millions of unique recordings are ‘at risk’ due to chemical decay and are becoming irrecoverable. Compounding the issue of tape degradation, original playback machines and spare parts are becoming significantly harder to find. This equipment obsolescence means that it will no longer be possible to play back an increasing number of tape formats.

At the Swiss Light Source, we use synchrotron X-rays to investigate magnetic materials. Based on X-ray spectroscopy, we are developing a non-destructive technique for the recovery of the audio signal from heavily damaged magnetic tapes in a contactless way, minimizing the risk of further damaging the tape. We have performed proof-of-concept measurements using circularly polarized X-rays by exploiting the X-ray magnetic circular dichroism effect at the Swiss Light Source and at the SOLEIL synchrotron. Beyond being contactless, our technique allows us to access information throughout the thickness of the tape and measure the magnetic state itself, rather than stray fields, which can be complex in damaged tapes. In collaboration with the Swiss National Sound Archives, we have demonstrated the feasibility of reading analog signals from ¼-inch tape. Furthermore, we successfully recovered signals from artificially aged and damaged tape, as well as from chemically degraded tape. 

We believe that our approach has the potential to enable the recovery of tapes damaged or decayed beyond the reach of other traditional digitization technologies. Further development of the technique will allow the recovery of entire tapes with high resolution in various multitrack formats using the same setup, thus eliminating the need for original readout equipment.