On 5/6/2015 9:51 AM, Pete Tinker wrote:
> Please forgive this uneducated question. Much of the discussion on this
> topic has focused on the "phase" of different transfers. I'm not a
> signal processing guy, but to me "phase" involves the frequency of the
> signal, so changing the phase is a temporal shift in the signal (a
> lateral shift along the time axis) by a fraction of some wavelength. At
> times in this discussion, it seems that the intention of changing the
> phase is a reversal of the amplitude of the digital signal (mirroring it
> across the time axis), for which frequency is irrelevant.
> If I have a stereo signal from a hill 'n' dale source, it seems the
> preferred next step is to invert the phase of one channel and then
> combine (add) the two channels prior to any digital noise reduction.
> What is the meaning of "phase" in this context?
This is a linguistic issue, more than anything else. In the last 20
years, the word "phase" has come to be used where "polarity" would
really be a more accurate description, and that'd hoe the word's being
used in this context. A hill-and-dale (vertical) recording has the
signal impressed on the groove vertically (duh), and when played back
with a conventional stereo cartridge it will deliver signals from the
two channels that are of opposite polarity. Combine the signals as-is
and the desired material (music) will cancel, leaving only noise.
Reverse the polarity of one channel, then combine them, and the desired
signal will remain while the noise (ideally) cancels.
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