Reversed Polarity

[TripleM]

I hear people talk about how, "Your polarity is reversed." Could someone explain to me what it is, what causes it, and maybe even what it sounds like?

Thanks.

[mixsit]

Oo, oo! ok, I know this one.

The sound waves swing positive and negitive voltages, the rate is the frequency. If two of the same sounds (or similar sounds, as in two mics from different distances on the same sound) are combine in phase, they add together. If one goes pos. while the other goes neg., they cancle out. If the are a little out of phase (as in the two mics above) they cancel some freguencies and add others.
Inverting the phase of one signal fixes the problem if they are exactly out of phase, but shifts the canceled/added frequencies if they are partly out of phase. Moving one track's position in 'time', is a way to adjust for partial phase differences.
...I hope

[tvaillan]

let's say your right speaker was plugged in wrong

i.e. the red wire was in the black hole and the balck wire in the red hole.

now let's say your left speaker is fine.

play the music and you get 180 phase shift on the right speaker.


anybody can comment on this?

is it a good explanation? or am i full of shit?

[Sennheiser]

" Everybody needs reverse polarity"

[littledog]

Originally posted by tvaillan
let's say your right speaker was plugged in wrong

i.e. the red wire was in the black hole and the balck wire in the red hole.

now let's say your left speaker is fine.

play the music and you get 180 phase shift on the right speaker.


anybody can comment on this?

is it a good explanation? or am i full of shit?

You were doing fine until you got to the "phase shift" part. That's where a lot of people get confused.

Phase shift is caused when a given sound is recorded or played back through two (or more) sources in such a way that one of them is shifted in time. If the timing is such that the waves are arriving 180 degrees out of phase with eachother (so that a positive peak on one signal is arriving at the same time as a negative peak) the resulting cancellations can very much resemble reversed polarity, and as such, can be "fixed" to some extent by flipping the polarity of one side.

But polarity has nothing to do with timing or phase. Polarity is when you create a mirror image of the wave form, which is often done accidently by miswiring one side of an input or output somewhere in the audio chain. (Could be the speakers, but could be anywhere else as well).

[TripleM]

Originally posted by littledog


Phase shift is caused when a given sound is recorded or played back through two (or more) sources in such a way that one of them is shifted in time.

Thanks dog. Maybe my question was really about phase shifting.

If possible can you describe how a "bad case" of phase shift sounds? How would I know it when I hear it?

Again - many thanks.

[martello]

Originally posted by littledog


You were doing fine until you got to the "phase shift" part. That's where a lot of people get confused.

Phase shift is caused when a given sound is recorded or played back through two (or more) sources in such a way that one of them is shifted in time. If the timing is such that the waves are arriving 180 degrees out of phase with eachother (so that a positive peak on one signal is arriving at the same time as a negative peak) the resulting cancellations can very much resemble reversed polarity, and as such, can be "fixed" to some extent by flipping the polarity of one side.

But polarity has nothing to do with timing or phase. Polarity is when you create a mirror image of the wave form, which is often done accidently by miswiring one side of an input or output somewhere in the audio chain. (Could be the speakers, but could be anywhere else as well).

I've heard of problems of phase when using 2 mics on the snare for example (1 top head 1 bottom head), but I don't understand how is it possible to create and to avoid these phase problems.
Thanx

[Tom Hicks]

The 2:1 rule says that two mics need to be minimum twice as far apart as the distance from the mics to the sound source in order to avoid phase problems.As in overheads.

[participant]

I thought that was 3:1; is there also a 2:1 rule?




Chad

[littledog]

The 3:1 rule is to avoid drastic phase artifacts.

The 2:1 rule is how you choose which college you should attend (at least two women to every man...)

We've all heard the kind of sound intentional extreme phasing can make if you've ever had one of those little phase shifter stomp boxes.

In recording situations, the result is usually a comb filtering kind of sound where some frequencies get notched whil e others get boosted resulting in a strangely hollow or otherwise un-natural timbre.

Any time a sound from a source is hitting two or more mics that are placed at different distances from the source, the potential for phase artifacts is there. That's why so many people here hate recording vocalists who want to sing while playing acoustic guitar. It's also a good reason to try using just one mic carefully placed to capture both.

[ambi]

hmm, so how would you knwo if you had phase reversal going on?> or the mics being outa phase or whatever it is that causes problems?
for instance, if my brother was playing guitar, and i miced his guitar with a shure sm57, and his voice with a condensor, say an apex 410. Would there be a possibility of phase problems? And could they be fixed? the phase reversal switch?

[littledog]

Originally posted by ambi
hmm, so how would you knwo if you had phase reversal going on?> or the mics being outa phase or whatever it is that causes problems?
for instance, if my brother was playing guitar, and i miced his guitar with a shure sm57, and his voice with a condensor, say an apex 410. Would there be a possibility of phase problems? And could they be fixed? the phase reversal switch?

Tsk, tsk, Ambi... you have not been paying attention in class! Repeat after me: POLARITY can be reversed, not phase. In your example you might very well have problems with your brother's voice being picked up by the guitar mic, which when mixed with the vocal mic makes his voice sound much worse than hearing the vocal mic alone.

If you go back and reread the discussion, you'll find two answers to your questions:

1) The polarity switch can be used to (sometimes) alleviate phase problems. If you are not sure if you are having those problems, a simple test is to flip the polarity switch on and off on one of the mics, and see which way sounds better.

2) Use the 3-1 rule when using two mics on one source whenever possible. This means having the mics at least 3x the distance from eachother as they are from the source. (Example: 6" from source means 18" from eachother). The important exceptions to this rule are when doing specific stereo mic'ing techniques like MS, XY coincident pair, decca tree, etc. If you don't know what those things are, then just stick to the 3:1 rule to be safe!

3) Consider using just one mic in some cases.

[destorctr]

polarity can be fixed by connecting cancelled sorces to a common ground

[TexRoadkill]

Originally posted by destorctr
polarity can be fixed by connecting cancelled sorces to a common ground

[destorctr]

it was ment as a question i forgot the ? i thought that if polarity of a mic was reversed and thus canceling out another mic that if you attached the mic cords to a common ground there would be no problem ? yes no ?

[regebro]

No.