Restoring 78 rpm shellac recordings of Arthur Paredes

Arthur Paredes - Pioneirismo, genialidade e modernidade is Tradisom's 316-page book on the Coimbra guitarist, with six CDs of music, much of it never released before. Our part was the transfer and restoration of 78 rpm shellac discs from the collection of João Pedro Almeida Rocha.

Before the stylus touches the disc

Every disc was assessed before playback: surface condition, cracks, warping, residue and label information. Discs were then cleaned and handled with gloves throughout, so that what reached the stylus was the groove, not decades of dirt.

Finding the original pitch

Early discs were rarely recorded at exactly 78 rpm, and recording speeds varied between studios and sessions. Played at the nominal speed, a disc can sound sharp or flat. That shifts the tempo, the timbre of the guitar and the pitch of the singing voice, so a singer can end up sounding in a different key, or even like a different person. For most of these recordings the original pitch was recovered with a custom analysis tool rather than by ear alone.

Archive copy and service copy

The work follows the conservation approach set out by Peter Copeland in the British Library's Manual of Analogue Sound Restoration Techniques. The unprocessed transfer is kept as the archive copy, a "warts-and-all" record of the disc as it sounds today.

A separate service copy is then made for listening. It corrects the known faults of the recording and playback chain (speed, equalisation, clicks, crackle and surface noise) while respecting, as far as possible, the sound the musicians and engineers intended. The archive copy is never altered, so any future restoration can start again from the source.