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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.

Peace,
Paul

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