How do I reverse phase a microphone if I have no reverse phase switch?

N

Nigie

New member
Question about reverse phasing microphones:

I'm on the verge of buying a hoontech c-port which has a pair of built in mic preamps in the outboard analogue/digital converter box.

If I use these preamps to record from one mic placed infront of my guitar speaker and one mic placed behind the speaker and I want to reverse phase one of the mics how is this possible on a preamp such as c-port's that doesn't have a phase reverse switch?

Is there an easy way round this? The c-port also has regular line inputs without preamps which I can use if this is relevant.

Thankyou to anyone who knows this basic stuff. This is a great forum!!!

Nige
 
why don't you just record it ??? in my humble experience you can't phase reverse a microphone, you can't phase reverse a mono signal.
bizz
 
I have the c-port also but there is not a "phase reversal switch" on it.If your software supports vst plugins I found a Phase reversal plugin this past summer on the cubase webring.Sorry I don't recall the name but I can assure such a thing is out there if you go looking for it.

Tom
 
Make very short cable (like 10cm) and wire it out of phase.
Now when you need phase reversal you just add that it into the chain. Voila! Instant phase reverse. This way you don't have to change the cable when you have already positioned the mic but need phase reversal.

Keijo
 
Sorry for my ignorance in my last post - of course you can phase reverse a microphone *DOH* - but the only situation I know of that you use it is when you make a ms recording, doesn't seem like that is what you wanna do, so please enlighten me - what do you gain from phase reversing one mic in the set up you described
regards
bizz
 
Bizarre - I'm about to expand your knowledge for you again...

You use phase reversal when using multiple mics for close-miking situations such as drums... anytime 2 or more mics are placed on the same source within a short distance of each other, there is a good possibility that there will be comb-filtering between the 2 mics -- flipping one of the mics out-of-phase (technically, not phase, but polarity, but everyone mis-uses the term "phase" so I'll jump in) will help minimize the filtering effects.

Bruce
 
Thanks Blue Bear
In situations where I've used several mics, I've delayed them. I'm gonna try that phase thing next time I'll get the chance.
bizz
 
Can using phase shift on a mic (in a 2 mic recording setup of, say, a guitar amp) adversely affect the recording if was not actually necessary? Does it matter which mic is reversed?
 
Bruce is right. A 'phase-reversal' switch or a cable you make to switch the 'phase' really is reversing the polarity. However, when you switch the polarity of one mic in a two mic setup, you are changing the phase relationship between the two signals, so the two are closely related.

Bizarre - using delay is probably a better way to deal with phase interference in a multiple mic setup. Its not like signals from two mics are either in phase or out of phase. There is the whole gamut in between and due to the fact that different frequencies travel at different speeds, the phase relationship between the two signals is different for every frequency you are recording.

Vurt- Yes, it can hurt. If your mics are in phase (you successful followed the 3:1 rule or just got lucky) switching the phase can cause comb filtering or loss of bass frequencies.

---------------------
You know, just thinking about this topic makes me wonder if it would be possible to develop software that would allow you to apply different length delays to different frequencies - a multiband delay I guess? Might be a useful tool. You could couple it with a spectral analyser of sorts that would tell you the phase relationship between two signals at any specified frequency so you could apply the appropriate delay. :confused: Does this already exist?
 
Yes, they do exist, but not in the typical price range familiar with Studio equipment. The programmable signal processors used in airborne RADAR (not to be confused with a hardisk recorder) can actually phase shift individual frequencies and even switch the polarization real time from 0 thru 360 degrees. How does a few hundred grand sit with ya, you would probably need DOD approval as well. So the answer is Yes, but tecnically here is why they are expensive. Each frequency is extracted thru a series of filters that strip and puts frequencies into bins or temporary folders, then you process each frequency independently, lots of compute cycles and lots of cards more than 15 cards, equal to having 20 PC's with dual processors, these puppies weigh anywhere from 55 lbs and up. The software really isnt where you costs are incurred but its the amount of A/D converters and amount of memory. Anyhow as usual Ive typed long enough.

Peace,
Dennis
 
out of phase mic wiring

I understand why one would wire a mic chord out of phase, however, could some one please refresh my old memory on just exactly how to do it. Thank you very much.

Rdparo
 
You are right atomictoyz. Couple of things:

- Phase reversal should not be seen as an effect, its a tool which allows you to put things IN phase, to avoid frequency cancellation.
For those of you unfamiliar with exactly what shiftin a phase does, just grab a speaker from your home stereo, and put it opposite the other speaker. If your low end disappears, one of the speakers is out-of-phase. Reverse a cable, the low end will appear - and the signal is in phase.
Wow, thats back to basics.

- There are much easier ways to accomplish phase reversal as an effect. This could be accomplished, for instance, by having a track and copying that track on a new one. Now use an EQ to isolate a certain frequency you would like to phase-reverse and play it back with the original track. If you have the right tools you could even sweep accross a certain spectrum. However, always consider that the effect will only work in multi-channel play-back, it will lead to cancellation in mono. In a more complex form, using logarithms, this can create a "virtual surround" room placement of a signal.
I have used such an effect on one of Uru's demos, a song called You Know, at http://www.mp3.com/uru If you listen to it in stereo, you will hear a strange placement of the voice, it appears to come from inside your head, rather than left / right speakers. Switch to mono and the voice volume will deminish severely, the effect will be gone, due to frequency cancellations.
It is audible on MP3, unfortunately the encoding has made the effect much less than normal red book format.
 
You must log in or register to reply here.
Back
Top