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Thread: Does PHASE matter on a single source?

  1. #11
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    There is no such thing as phase with a single source. Phase is a relationship between two or more signals. If hitting the button makes a sound difference, you are monitoring at least two things. Either you are changing the phase relationship between the bass and the other instruments in the song, or you are monitoring the bass live and recorded.
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    Quote Originally Posted by ecc83 View Post
    Polarity flips can also be useful to combat feedback in a mic/speaker PA setup.

    Set gain so the systems is just at the ring point then flip the mic phase/polly. The ring should get better or worse. If possible repeat the exercise for the speaker polarity (rarely have the option these days) You can often get up to 6dB more gain before ring with this technique.

    If you cannot decide which is "flipping best" go for the lowest ring note.

    This reminds me. I did some tests with mics a couple of weeks ago and I suspected the Behringer 8500 dynamic was OOP with the rest of my mics? Must check into that.

    Dave.
    This is exactly what i meant.
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    Quote Originally Posted by Gtoboy View Post
    This is exactly what i meant.
    Did you? I thought your question was about RF interference, noise etc? Please amplify Mr G!

    Dave.

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    I remember my old Fender amp had a 'phase' power switch (old amp with a only an ungrounded 2-prong power plug), so it was used to quiet hum, just reversing the + and - connections.
    A phase switch on a DI is to stop feedback, as Dave said. The reason it can make the sound seem different is the signal coming out of the speakers/headphones is now either (almost) perfectly in phase (increasing some frequencies' volumes) with the original sound you are hearing, or out of phase, reducing some of those frequencies due to phase cancellation. Did I mention I hated Wave Physics in college?
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    I would say that a polarity switch on a DI is for whatever use one might need a polarity switch. I would most likely use it to make the DI work with a mic on the amp.
    Last edited by bouldersoundguy; 09-20-2020 at 16:55.

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    I have done the checks and the Behringer is definitely wrong polarity when used against a Sontronics LDC and a Prodipe TT1.
    I then made up a polly flipped XLR-XLR cable and that sorted the XM8500. I shall buy another one soon just to check mine isn't a Friday afternoon lemon.

    Dave.

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    One thing I have experienced concerning phase on a single source occurred on an acoustic/electric Epiphone Guitar with volume, bass, mid-range, and treble sliders on the guitar's body. It also has a "phase" switch which, according to the instructions, can be operated to reduce feedback when the guitar is close to the amp. That switch somehow changes the phase between two pickups or something like that to cancel feedback. It's more complex than simply reversing the polarity or phase on a single pickup, since such a simple reversal would immediately go out to the amp and do us no good for cancellation of feedback. I'm sure that this matter is more involved than I understand, so I will be interested in hearing more about it.

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    Quote Originally Posted by hautbois16 View Post
    I'm sure that this matter is more involved than I understand, so I will be interested in hearing more about it.
    No Iím sure itís far less complicated than youíre trying to make it. Itís the same thing ecc83 talked about above. Flipping polarity might help with gain before feedback, but only kind of accidentally, probably only at certain frequencies, and definitely only until you move either the guitar or the amp.

    I read a thing a while back where Brian May talked about using his pickup phase switches in a kind of interesting way. Now, if youíre playing through just one pickup, the absolute polarity is pretty much arbitrary and doesnít matter. Flip it one way, record, flip it the other way, record, compare the two, hear no meaningful difference. BUT if youíre playing in front of a loud amp, and you hit a note and hold it and it goes off into that self-oscillating feedback thing, and you flip the switch, it might just cause the held note to break to a harmonic. The harmonic mode of an eBow is very similar. The driver is opposite polarity to the sensing coil, so it is kind of driving against itself, which magically causes the first harmonic to jump out.

    Now, if you happen to be pushing an asymmetrical waveform into an asymmetrical limit, the polarity of the input does make some difference. If the higher side of the wave goes one way, it hits the limit sooner than if it goes the other way. Itíll be noticeably more distorted. But if the limits are symmetrical, then it doesnít matter, and if itís not hitting the limit in either direction anyway, then it doesnít matter and wonít be audibly different either.

    But yes sometimes polarity matters between different sources. A kick drum and a bass, or even a bass guitar and a guitar might work better together one way or the other. Itís pretty much accidental again, and if thereís any amount of timing slop, it could be different for each hit, but bass waves are long enough that it could be a matter of degree rather than full reversal from note to note.

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