[78-L] Sound Remaster and Restoration

[Chris Zwarg]

>    I record all recordings in stereo, so I can use the best track
>later for restoral. 

For mono disc recordings (78 and microgroove) played with a stereo cartridge, a 1:1 mix of both channels will usually give the best sound, as the (identical) signals add up and reinforce each other, while the (random) noise doesn't, so you gain about 3dB signal-to-noise ratio. Spurious vertical stylus movement caused by a rough or bumpy record surface or by over-recorded loud passages will cancel itself out completely, reducing rumble problems and end-of-side distortion. Only with a badly worn copy or a defective original recording, one channel can occasionally be so much worse than the other that it is advisable to work with the "good" channel only. Even in such a case, adding the poorer channel at lower volume or with reduced treble can give at least part of the described benefits without carrying the defects audibly into the result.

Mixing the two channels should always be done AFTER declicking (as smaller clicks will often appear in one channel only, and it makes more sense to remove such clicks from the offending channel only rather than from the mix), but BEFORE denoising (as part of the noise will cancel out anyway by mixing both channels, so the digital denoiser has less work to do afterwards and will correspondingly cause less unpleasant side-effects).

Note however that dual-mono analogue tapes (i.e. mono signal recorded onto a two-channel "stereo" tape, as on a standard compact cassette) MUST NOT be mixed-down, as tape - and especially cassette - channels are never 100% in phase with each other because of the mechanical frailties of the system, so a mixdown would cause audible "phasing" effects and a drastic loss of treble and clarity. With such tape recordings, the poorer channel should simply be discarded. BTW: Manually adjusting the playback head with a small screwdriver for maximum treble response will make a BIG difference when transferring cassettes!

Chris Zwarg