Topic: Phase inversion....why/when?

[Nick's Picks]

curious..

most studio level (and some portable) preamps have phase inversion switches.
why ?
when would you want to use this.  I understand what it does, but I dont understand why someone would want to use it.

[Chuck]

When mixing several souces together phase becomes very important.
An example:

Mixing a SBD feed with an audience microphone feed. You may want the phase to be reversed on the microphone feed as the PA signal may be out of phase with your microphones.

[bluegrass_brad]

When doing sound I most often use the phase reversal on the drum kit mics.  Some guys bring in a bunch of mics for their kit, and with that many mics phase can be an issue. I try to keep it simple with a kick, snare, HH, OH, OH, and Tom. But some guys want every little toy mic'ed, so what can you do.  It has also comes in very handy with acoustic instruments that have both an internal mic and a pickup.  Sometimes they will be out of phase.  During sound check I always check phasing on  these types of things.  Sometimes the difference is night and day.  It has also been helpful in a situation where a band is doing a single mic style show, except I like to run xy cards right underneath the LD mic so I can get better coverage.  There have been times when doing this that it sounded much better with the LD out of phase to the SD's down below.

[kskreider]

When mixing several souces together phase becomes very important.
An example:

Mixing a SBD feed with an audience microphone feed. You may want the phase to be reversed on the microphone feed as the PA signal may be out of phase with your microphones.

qft.  I see this a lot.

[BayTaynt3d]

You might need it if you've got a V3 running in front of it, LOL! I kid, I kid...

[anodyne33]

Brad hit it on the head for drums. In my case mixing in a small club I get a TON of bleed from all the instruments on stage through the vocal mics. Sometimes switching the phase on the vocal mics can help keep some of the guitar out of the house. In the studio we'd do two or three mics on a guitar cabinet at one time and flipping the phase on them in different combinations could give wach one different tonal qualities in relation to the others.

[Charlie Miller]

When mixing several souces together phase becomes very important.
An example:

Mixing a SBD feed with an audience microphone feed. You may want the phase to be reversed on the microphone feed as the PA signal may be out of phase with your microphones.

That's the first thing i check when doing my mixes. Adding stage mics can throw phase out of whack very easily. Sometimes you only need to swicth on channel.....sometimes 2....cm

[dunebug81]

how can you tell if youre mixing two sources that they are out of phase from each other?

[kskreider]

how can you tell if youre mixing two sources that they are out of phase from each other?

When you have the waveforms lines up, one wave form has a 'valley' where the other has a 'peak'.

[Chuck]

When mixing several souces together phase becomes very important.
An example:

Mixing a SBD feed with an audience microphone feed. You may want the phase to be reversed on the microphone feed as the PA signal may be out of phase with your microphones.

That's the first thing i check when doing my mixes. Adding stage mics can throw phase out of whack very easily. Sometimes you only need to swicth on channel.....sometimes 2....cm

Yeah, my comment was aimed at what most folks here would use the phase switch for. As Brad and other pointed out it is invaluable when mixing many different microphones/ sources togther in a more complex application. BTW, I suggest to Jon at Naiant.com (the guy that makes the MSH-1O's among others) to include a phase inverter in his product line. Now he does: http://naiant.com/studiostore/cleverdevices.html
The cost per device is $12.

[Nick's Picks]

interesting.
I guess that it wouldn't be anything we would use "in the field" ... for the most part then.  dealing w/just two channels and all.

+T

[Charlie Miller]

how can you tell if youre mixing two sources that they are out of phase from each other?

I always try flipping the phase on one channel to see how it sounds. That's a good way too tell....

also, you would be surprised how many sbd's are out of phase.....

[dunebug81]

how can you tell if youre mixing two sources that they are out of phase from each other?

I always try flipping the phase on one channel to see how it sounds. That's a good way too tell....

also, you would be surprised how many sbd's are out of phase.....

interesting, Ill have it give it a whirl the next time i mix two sources.

[Church-Audio]

interesting.
I guess that it wouldn't be anything we would use "in the field" ... for the most part then.  dealing w/just two channels and all.

+T

As long as you have separate tracks "absolute polarity" people refer to it incorrectly as phase :_) can always be fixed in post. But once you mix the sources to stereo that's it. So if you have more then three mics and they all have there own tracks polarity is not important until you get home and mix it down. Then you can try and reverse things. But if you can do it at the mic input of a preamp that is always the best way. Because sound cards/Digital uses a process that can change the sound. 

This is why good consoles and good mic preamps have Polarity switches because when it is inverted in the input stage of a preamp its absolutely correct with no discrepancies when its done in the digital domain depending on software/hardware sometimes errors in phase are introduced because the signal is not 100% converted to 180 degrees it might be 179.9 this is called phase error, and its not a big deal if its a very very small amount of error, the real problem is when its not so small of an error and all of a sudden your recordings sound like crap. So its always better to do it at the event (polarity) if possible EDIT. But you need a good set of headphones and a good set of ears to hear it sometimes, other times its as plain as black and white..

[RebelRebel]

This is why good consoles and good mic preamps have Polarity switches because when it is inverted in the input stage of a preamp its absolutely correct with no discrepancies when its done in the digital domain depending on software/hardware sometimes errors in phase are introduced because the signal is not 100% converted to 180 degrees it might be 179.9 this is called phase error

http://www.turneraudio.com/tech/phase.html

http://www.sfu.ca/sca/Manuals/ZAAPf/p/phase.html

http://sound.westhost.com/pcmm.htm