Impact of phase inversion by preamp

George Louis the Polarity Pundit debunked himself in our room at CES about 10 years ago. He walked in, claimed our system was out of phase, so I said OK- here its in phase then and clicked the switch. Then he claimed you couldn't hear it on LP, so I said OK, here's the same track on CD. Then he claimed you couldn't hear it if it was an analog tape source and quickly left with us laughing in his wake. Funny thing is the recording is done with minimal mics in true stereo; it was easy to hear which position was right- it was George who could not. Irony is apparently still *in*.

You seem to support my assertion that 50% of all recordings are in absolute polarity. Thus the need for a polarity (phase) switch.

I meant that I marked polarity on the jacket, not that the LP itself was marked.

OK- that makes more sense.

I forget most of the details now, except some discs were inverted polarity relative to others, verified with an oscilloscope.

How did you do that? You had the master tape?

For a long time, LPs were marked as to preferred polarity. They encompassed the full gamut of recorded music from Pop to Opera.

Could you name one? I have a lot of titles in my collection and don't recall ever seeing that. The manual for my lp cutter electronics mentions nothing about it as well.

Nonsense.
I polarity tested and corrected all the microphones.
I verified all the lines and electronics.
I made the recordings.
Some recordings were M-S, X-Y, spaced pair and some multi-mic.
Synthesizers are easily polarity checked with a sawtooth wave.
The tracks were 100% polarity correct.

Keeping in mind the simple fact that we've had a polarity switch on our preamps longer than anyone else in the world:


OK- If you have that sort of control you can pull it off (although the comment about synths is right out- don't go there- synths do all sorts of things with phase, pitch bending and portemento! However:

Added effects do not alter the polarity of a recording any more than an acoustic hall alters the polarity of the instruments on stage. The phase of an effect may differ from the signal, but the polarity remains unless purposefully inverted.

Reverb, phase shifters (think about what a phase shifter does...), EQ and the like can and do invert phase simply out of the design of the circuit, the number of gain stages and so on. If these effects exist on some tracks and not others, absolute polarity is easily lost. Now if you pay attention to those effect devices and compensate for their polarity (excepting phase shifters!), then you can make it happen.


But you are one in a million when it comes to this sort of thing! IOW with effectively all multi-track recordings you can't here absolute phase.

Then I would say that the speakers may not be well aligned. The point of the mentioned test was to determine the audibility of polarity. We used polarity correct recordings of acoustic instruments, 80's pop with all live players recorded with polarity correct mics, analogue reverb [plate and chamber] and 80's pop with drum machines, synths, digital reverb and effects. The polarity correct channel inversion was a side show to demonstrate that identical seldom exists.

This statement is false. In the recording studio there is no guarantee that a certain track is inverted polarity or not. Many mixboards have polarity inversion switches, but they are there for effect, not get assure correct polarity. Some channels go through effects like reverb or phase shifters and no telling what polarity the signal is when exiting that.

In short, with any multi-channel recording all bets are off when it comes to polarity. Its a mixed bag, plain and simple.

Nothing is completely passive. The more revealing the circuitry, the more it exposes component 'flaws'.

Experience with phase flip switches in active and passive balanced hardware often left something to be desired in terms of routing and hence inaudibility.

Making both halves of a balanced circuit identical is EXPENSIVE. Add in tube vagaries and the probability of a sonic delta is fairly certain.

These statements are by no means universal truths :)


'Passive' refers to a component that does not involve a semiconductor or vacuum tube. Switches, sockets, capacitors, resistors, volume controls, transformers, wire and the like are considered *completely* passive.


Our MP-1 preamp was the world's first balanced line preamp for home use. The phase switch has been on it since its inception 30 years ago. Quite simply, operating the phase inversion switch is subtle- on multi-channel recordings you can't hear any effect at all. IMO whatever your experience was, it would seem to have been done with equipment that wasn't thought out all that well.

We use differential circuits for our balanced operation. This is not particularly expensive to do- our preamps are pretty affordable compared to the competition in the same class! It is true that each half of the differential amp is slightly different, but you might be amazed at how well they work- the key is a good constant current source, with which we get Common Mode Rejection Ratios (CMRR) in the neighborhood of 100dB, which is pretty good. In a nutshell, no 'sonic delta' when the inversion switch is used (unless playing a true stereo recording); but even if the differential amp is poorly balanced, its a simple fact that there is no 'sonic delta' anyway; you might want to think about why; hint: it has something to do with differential amplifiers :)

In a balanced preamp the phase switch simply redirects the inverted phase to the non-inverted circuitry and vice versa. Its completely passive.
With many recordings the correct position is inaudible, owing to the recording being multi-tracked and mixed. The phase may be different depending on the instrument playing! So usually you only hear it on true stereo recordings, those done with only 2 or 3 mics (the latter being the Mercury process or Decca stereo tree, that sort of thing). The problem is that 50% of all recordings regardless of the media are not in absolute polarity while the other 50% are. Switching your speaker cables around to deal with this is a pain which is why we included the switch since we were making a balanced line preamp anyway.
You just have to try it and see. I seem to hear it easier with brass instruments.