phantom power and phase

[dr.colossus]

since i DON'T record to computer, and i have NO phase switches on my console or pres, i am going to have to make some "phase reverse" leads... i am fairly certain this is simply done by swapping pin 1 and 2... if i run these with phantom power to my condensor mic, am i likely to do any damage? is phantom power a.c. or d.c.? which pins does the phantom power run through?

fairly elementary questions, probably stuff i should know but have had trouble establishing a definate answer... cheers gents.

 

[DigitMus]

Phantom power (usually) puts +48vdc on pins 2 and 3, the ground is on pin 1. To reverse the polarity (i.e. put the signal 180º out of phase) swap pins 2 and 3 on one end of the cable you're making/modifying. I've done this about half a zillion times in the last 25 years with no ill effects.
Do not swap pins 1 and 2, this could hurt something expensive, or at least make a less than desirable noise.

 

[Flatpicker]

You could take a male and female XLR connecters from an old mic cable and make a "phase" adapter by connecting them with a short piece of cable, crossing pins 2 & 3.

 

[dr.colossus]

your'e right, pins two and three, they were the pins i was thinking, i just got the numbers mixed up. thanks

 

[Enchilada]

This is probably the wrong forum to be asking this but, meh.

What does reversing the phase actually do. Why do you need to do it. I've read that if you have a mic on the top and a mic on the bottom of a snare then you should reverse the phase of the mic on the bottom.
Do mics mess with each other of they are to close together?

 

[Light]

Well, first of all it is not phase, but polarity.

Look HERE.


Light

"Cowards can never be moral."
M.K. Gandhi

 

[dr.colossus]

good link light... just one question, in my situation, once the track hits the pre/mxier its all unbalanced, so in mixdown i may notice a phase issue i missed during tracking, but i'd be working unbalanced so how can you inverse polarity on an unbalanced signal?

 

[Enchilada]

Well, first of all it is not phase, but polarity.

Look HERE.


Light

"Cowards can never be moral."
M.K. Gandhi

What is phase reverse then? I have a phase reverse button on my preamp

 

[boingoman]

What is phase reverse then? I have a phase reverse button on my preamp

It's really polarity reverse. I don't know why manufacturers call it phase reverse, but I think it's because the term has been used so often to describe polarity reverse.

 

[boingoman]

good link light... just one question, in my situation, once the track hits the pre/mxier its all unbalanced, so in mixdown i may notice a phase issue i missed during tracking, but i'd be working unbalanced so how can you inverse polarity on an unbalanced signal?

It works the same way. When you switch polarity in a balanced signal, you are switching + and -. When you switch polarity in an unbalanced signal, you are switching + and -.

 

[Big Kenny]

you guys are talking about phase cancellation when you speak of the double micing thing.....

 

[sile2001]

It's really polarity reverse. I don't know why manufacturers call it phase reverse, but I think it's because the term has been used so often to describe polarity reverse.

Actually phase reverse is a valid name for it. Polarity refers to electrical charge, phase refers to the sonic characteristics of a waveform. Reversing the polarity of an electrical signal causes the phase of the waveform that signal represents to be reversed.

So it's still phase reverse

 

[acorec]

Actually phase reverse is a valid name for it. Polarity refers to electrical charge, phase refers to the sonic characteristics of a waveform. Reversing the polarity of an electrical signal causes the phase of the waveform that signal represents to be reversed.

So it's still phase reverse

You beat me to it. The naming comes from the perspective of what happens to the *waveform* and not the electrical characteristics.

 

[bgavin]

Some of the DI boxes, such as my Countryman Type 85, operate in reverse polarity.

 

[dr.colossus]

It works the same way. When you switch polarity in a balanced signal, you are switching + and -. When you switch polarity in an unbalanced signal, you are switching + and -.

hmmm. i've only had time for a little research but the "monster" cable site mentions something about requiring a "phase splitter"..... besides i always thought of unbalanced as + (hot) and ground, where balanced is + (hot), - (cold) and ground... where the entire waveform passes through just one line with the virtual (x,y?) axis removed, and in order to flip the signal the waveform would first have to be split into + and - across the axis then reversed then back to unbalanced... i guess the real world of electronics isn't as complicated as the one in my head

 

[Light]

Actually phase reverse is a valid name for it. Polarity refers to electrical charge, phase refers to the sonic characteristics of a waveform. Reversing the polarity of an electrical signal causes the phase of the waveform that signal represents to be reversed.

So it's still phase reverse

Nope, phase reverse is an absolutely horse shit name for it, because it does NOTHING to the phase relationships of the signal.

Phase is an issue of time, polarity is an issue of electrical charge. You can not fix an issue with one by using the other. There is no way to "reverse" phase. Phase is TIME based, and unless you have a flux capacitor, and a really good imagination, you can not reverse time. They are completely separate phenomena, and while they can affect one another, they do not do the same thing. Inverting phase does not, and can not, change the time relationships between two signals.

The problem is, when people learn about this stuff, it is always shown using sine waves, which make it very simple. And with a sine wave, 180 degrees out of phase looks an awful lot like reversed polarity. Unfortunately, there is not a naturally occurring sound in the world (nor most synthesized sounds) which acts like a sine wave. They change over time. Add to this the fact that no phase issue are 180 degrees out of phase at any important frequency, and never 180 degrees out at all frequencies (think about it, it is physically impossible).

The fact is that, while the polarity switch may fix an issue at one frequency, it will ALWAYS double the problem at another frequency within the harmonics for the same pitch. The major problem with calling the polarity switch a "phase" switch is that it leads to a major misconception amongst many engineers (both experienced and inexperienced) that it will "fix" phase issues. It will change the relationships, but it will not eliminate the problem. Try it both ways, and see which sounds better, but if you still have a problem, you may have to do some playing with where in time the parts if the track exist, as that is where phase issues come from. I only hope you tracked those multiple mics to separate tracks if you do.


Light

"Cowards can never be moral."
M.K. Gandhi

 

[Light]

i guess the real world of electronics isn't as complicated as the one in my head

No, it is. There is no easy way to invert the polarity of an unbalanced signal. However, if you are going into the mixer with balanced lines, you can simply use polarity reversed adaptor (or cable, or what ever) to invert it before it even enters the desk.

By the way, polarity relationships are very important when mixing, and not just between two similar signals. I frequently find that, if I have a track which is just not fitting in to a mix for some reason, even though the part is good, I can make major improvements by simply inverting the polarity. This is most obvious with similar parts (a guitar part and a high strung double, for instance), but can also be true with very different parts (vocals and bass, for instance). Sometimes a simple change in polarity can make a part "fit" in a way that it did not before. Try it both ways, and see which sounds better.


Light

"Cowards can never be moral."
M.K. Gandhi

 

[Enchilada]

I kind of understand now.
Thanks guys.

 

[dr.colossus]

No, it is. There is no easy way to invert the polarity of an unbalanced signal.

so it isn't just a matter of swapping the pins (for unbalanced). i'm quite interested in inverting the polarity of an unbalanced signal, and since there is no "easy" way, could you spare a moment to explain how it could be done practically (or theoretically), just as a point of reference... i think it would be a useful tool for my mostly unbalanced (there's a pun in there somewhere) studio...

 

[boingoman]

so it isn't just a matter of swapping the pins (for unbalanced). i'm quite interested in inverting the polarity of an unbalanced signal, and since there is no "easy" way, could you spare a moment to explain how it could be done practically (or theoretically), just as a point of reference... i think it would be a useful tool for my mostly unbalanced (there's a pun in there somewhere) studio...

I'm pretty sure it is as simple as switching the leads in an unbalanced cable. After all, if you wire one of a set of speakers in reverse polarity, you get the phase cancellation issues.

In an unbalanced cable, cold and ground are the same wire. Switch the leads, switch the polarity, by definition, I think. At any given instant, the voltage is swinging the opposite direction than an identical circuit wired with correct polarity.

Someone beat me if I'm wrong.