>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?
Phase is almost completely meaningless in this context.
BTW, it is the polarity that is switched among the two channels in a stereo cartridge to get correct replay for lateral or hill & dale, vertically cut records.
Phase has nothing do do with this at all.
Nominally, the cartridge should respond with the exact same frequency response for vertical modulation as for lateral modulation.
But there is always slight differences between lateral and vertical modes when this is actually measured using a test disk contaning a frequency sweep twice, first in lateral mode then in vertical mode.
Generally such differences that do occur gives rise to less than 45° phase shift at around 20 kHz.
Most of the time it is below 30°.
Such small amounts of phase shift will not make any big problems when the two channels is connected in polarity, L+R, for lateral cut disks or inverted polarity, L-R, for vertically cut disks.
If anyone is trying to correct for this type of error then you will find that the error changes with the test disk so a perfect fit on one test disk gives a totally different result on another test disk at those high frequencies.
So not feasible to do and is best forgotten.
What is important is to make sure that the two channels are connected together with the same volume as this will reject most of the unwanted signal.
The use of passive summing using an Y cable should be strongly discouraged as a moving magnet phono cartridge must see the proper 47KOhm loading and some amount of capacitive loading for the flattest possible frequency response.
Connecting both channels from such a cartridge passively using an Y cable will load the cartridge wrongly that will upset the frequency response.
Each channel should see the proper loading, 47 KOhm, given by a dedicated phono preamplifier and the polarity summing L+R for horizontal cut records or L-R for vertically cut records should happen electronically inside the preamplifier.
Finally, people seems to be totally confused about the fact that channels should ALWAYS be connected either L+R or L-R BEFORE doing any digital declick, decrackle, or hiss reduction.
Simple vector analysis learned in school tells that this is so no matter what anyone thinks here.
You always, without fail, gets rid of most of the unwanted noise by doing so including most of the audible distortion.
Signal, which is correlated between tracks adds +6 dB when summed while the noise which is uncorrelated between channels increases ONLY +3 dB giving you a net gain of +3 dB of the wanted music signal.
NO EXCEPTIONS whatever to how this works.
On lateral cut disks you remove ALL the pinch effect distortion too including ALL the vertical rumble component.
As has already been stated the vertical component on lateral cut disks has ONLY distortion and clicks. There is ZERO musical content here which means that disks SHOULD ALWAYS be replayed L+R for the best result.
Also for vertically disks then the music is ONLY in the vertical direction so MUST be replayed using L-R summing in the preamp used since the lateral signal has NO music at all.
Simple vector analysis proves this ALWAYS with NO EXCEPTIONS whatsoever.
The Mastering Room AB
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