Yes, and it's even sometimes very difficult to know if I'm really out of phase... Sometimes the Waves PAZ Position analyser detects a brief out of phase signal, and when I read the same location again, he doesn't see it...

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3singes
I'm finishing the LP mix/mastering. All the low frequencies are in mono under 300 khz. I also removed all the frequencies under 50 hz and above 16 khz.

I still have a little bit work on the phasing, but it's nearly OK. It seems almost impossible no absolutely never be out of phase. It happens very briefly sometimes.

If you are going to press vinyl, then don't bother trying to master it yourself. There is no point in it. Mastering for vinyl involes cutting the disc that gets electroplated to make the stampers the vinyl is pressed from. Go to a pro or let the pressing plant do it, which they have to do anyway in order to press your record. You might end up doing things that they'll have to compensate for and the sound will suffer. Just send them the best mix possible and let the disc cutter worry about all the tweaking. Sometimes it takes a couple of test pressings to get it right.
Self mastering is kind of like being your own attorney, rarely a good idea.

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3singes
Yes, the pressing plant (it will be MPO in France) always does a mastering.
But I think I can't give them a mix full of phase problems for example... This can't be corrected by mastering the stereo track of each song.

The problem of test pressings is that they are very expensive, like 500 euros..

Why would your mix have phasing problems in the first place? If that's the case, then theres a problem with the recording or in the system it was mixed on. Phasing shouldn't be an issue if you mix down several tracks to two track stereo with the bass down the center. It seems to me that by messing with it you're just overprocessing it and creating problems for the mastering engineer.

That's very expensive for test pressings. You could get accetates made instead, much cheaper. Have you looked elsewhere in Europe? Surely eastern Europe is less expensive?

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3singes
There can be phase problem in the first place. For example, the drums have been recorded with a mic on each drum + overheads + a stereo mic above the drumset and another stereo mic in the room. this gives a very great natural sound, but also can create phase problems.

The bass, bassdrum and snare are in the center. The guitars are paned very much to each side.
Reducing the stereo width often helps reducing out of phase signals.
But sound is complex... sometimes everything is OK when you analyse each intrument separately, and when you put everything together, it goes out of phase, because you analyse the total stereo image.

The prices in Eastern Europe (GZ) are the same, I even got cheaper prices here.
I will ask about the accetates.

Any Phase problems caused by microphones need to be caught and corrected at the time of recording. Phasing during mixdown can happen because of excessive bleed from other instruments, but again this should be addressed at the time of recording. Trying to fix it later, you just end up butchering the sound. In my opinion, it is fruitless to analyse each instrument separately, they should be analysed in context. They have to sit well together, so any eq changes should be made with respect to the other instruments.

I'm not trying to tell you how to do this, I realize there are many valid approaches. These are my opinions based on my experience, so forgive me if I come off wrong way or rude. Good luck with your recording, may the audio gods smile upon your project.

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Here's what the Waves PAZ user guide says about anti phase :

"It is a bit tricky to define when a signal is shown by the Stereo Position Display or heard by the ears as “out-of-phase”.
This is not simply when the left and right channels happen to have opposite polarity at any given instant. Such a
situation can happen if independent instruments are panned to different stereo positions, and it just happens,
statistically, that the signal of each channel has opposite polarities. The meter will show a quick spike in the antiphase
area. This can also happen if a stereo delay or reverb is applied to an instrument and the delays arrive to each channel at different times.
In these examples, the ears do not hear a disturbing ‘out-of-phase’ sound. For us to hear an out-of-phase sound,
there generally needs to be a consistent opposite polarity over a period of time, which the meter will show.
The Stereo Position Display analysis takes this into account. Still there will be occasional fast spikes in the antiphase
region, and you can ignore them if they are not consistent, especially if you know you are using stereo delay or
similar effects. You might be really bothered if the energy in the out-of-phase region is consistently significant
compared with the energy of the ‘in-phase’ region."

For example, if you analyse only 2 drumset overheads mics, the PAZ position analyser will show many out of phase signal.

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