Vinyl mastering is more art-form than science, it's a strange mix of psycho-acoustics, physical engineering and high-end electronics... here's a brief explanation of
some of the forces, issues and solutions.
PHASE CORRELATION A stylus reads stereo information (two channels of audio) out of one groove. The left channel audio is reproduced when the stylus moves in one direction whilst right channel information is transferred in a perpendicular direction.
The problems arise when a track is required to be cut loud, like most electronic music. In this case, out-of-phase low or high frequencies above a certain amplitude, can actually cause the stylus to get 'pinched' (jump out of the groove), or alternately, make it end up losing contact with one or both sides of the too-wide groove (resulting in distortion and general badness). The Mastering Engineeer dealing with a track that has badly uncorrelated audio will have to use a Vertical Amplitude Limiter, which sums frequencies below a variable crossover point to mono when they go over a set amplitude threshold, or an Elliptical Equalizer, which sums all bass frequencies below a specific crossover point.This, like any phase altering procedure, can have the effect of diminishing the stereo-field of the audio, which menas it won't sound quite right. Of course the other option is to just cut the record at a quieter level and leave the majority of the stereo image untouched. If these phase issues are addressed at the production level then a much more authentic record can be achieved on vinyl.To check if your mix may have such phase issues you can simply use your waveform editor; Select one channel (left or right), invert/flip that channels waveform and then mix both channels into a single mono soundfile. All the audio that was similar between both channels (mon0) has now cancelled itself out and what you hear is any out-of-phase contingents in your track. You can run a spectrum analysis if you want to see exactly which frequencies are present, but it should be plainly obvious if there are any really loud bass frequencies or some high-end problems present. |
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