Restoration Tips & Notes Working with audio media (mostly tape) restoration

2012-01-06

Capturing both directions of a half-track mono tape

Filed under: archival practices,matching head to tape,recording/mastering — Richard L. Hess @ 15:39

It is possible to capture both directions of a two-sided half-track mono tape in one pass.

The critical factors are:

  • Azimuth
  • Direction
  • Polarity

The azimuth of both sides needs to be the same. If the two sides were recorded at different sessions and/or on different machines, then there is no guarantee that azimuth will be the same on both sides. In a large-volume project, this can be addressed by installing two repro heads, one for each direction, and adjusting azimuth separately. This does not work well for stereo tapes with different azimuths because any temporal perturbations in either the recording or reproduce passes will result in severe stereo image shift. If a record head had azimuth scatter between the two channels, it is best to split the difference, if possible without severe high-frequency attenuation.

Obviously, the direction of the playback needs to be reversed in the DAW (Digital Audio Workstation) software, but that happens pretty quickly on a current computer.

Not-so-obviously, the polarity of the signal is also reversed when played backwards. That, too, can be addressed, possibly in the same pass or, worst case, a separate pass in the DAW software.

This is not recommended for any tapes using noise reduction such as Dolby or dbx, nor for the highest quality of music. However, most two-track tapes recorded on both sides are not of this quality.

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