Phase Issues?
- Thread starter UnkleSlam
- Start date
Gidge
Lapdance Test Dummy
I stole this explanation from another website:
Phase is a very important and often misunderstood factor in recording. Imagine the complete cycle of a sound wave as being like a wave in water. This wave has a crest, which pushes on your eardrum, and a trough, which pulls on your eardrum.
If two signals are electronically out of phase their waveforms can be mirror images of each other. When this happens, there can be cancellation of all or part of your sound. As the crest of waveform A pushes on your eardrum, the trough of waveform B pulls on your eardrum with the same amount of energy. This results in either no movement of the eardrum (no perceived sound) or reduced movement of the eardrum (altered, inaccurate sound).
If two waveforms are in phase, they crest and trough together. This results in a doubling of the amount of energy from that waveform, or twice the amount of air being moved.
When multiple microphones are used in the same room, sounds can reach the different mics at different times and probably at different points in the cycle of the wave. They combine at the mic out of phase. That's why it’s always best to use as few mics as possible on an instrument or group of instruments in the same. Fewer mics means fewer phase problems.
This theory also pertains to the way speakers operate. If two speakers are in phase and they both receive the identical waveform, both speaker cones move in and out at the same time. If two speakers are out of phase and if they both receive the identical waveform, one speaker cone moves in while the other speaker cone moves out. They don’t work together. They fight each other, and the combined sound they produce is not reliable.
This problem doesn’t show up as much in a stereo mix, but anytime your mix is played in mono or anytime you are combining multiple microphones to a single tape track, this can be the worst problem of all. To hear the effect of combining a sound with itself in and out of phase, listen to the guitar in the following audio examples. First, is the original track playing into one channel of the mixer. Next, the signal is split and run into another channel of the mixer. Notice the volume increase as the two channels are combined. The final example shows the sound difference as the phase is reversed on the second track. When combined, the tracks are obviously thin and reduced in level. Imagine if that happened to the guitar track in a mix as it was played on mono AM radio.
The nature of combining sounds dictates that there is always phase interaction. We wouldn’t want to hinder that because good phase interaction gives our music depth and richness. However, we do want to be particularly aware of phase interactions that can have an adverse effect on the quality of our music.
If your mixer has a phase switch on each channel, it’s probably at the top of the channel by the preamp and attenuator controls. Its purpose is to help compensate for phase interaction problems. For practical use, listen to your mixes in mono. If you notice that too many instruments get softer, disappear or just seem to sound funny in mono, then there’s probably a phase problem between some of the tracks. Change the phase of some of the tracks that might be combining in a problematic way until the mix sounds full and smooth in mono.
Short delay times, chorus and phasing effects can also cause these kinds of problems in mono, so you might also need to change some delay times to help even things out. There will be more about this when we cover mix-down. Once you’ve located and solved the phase problems, your mix will sound just as good in stereo, and you’ll be ready for television or AM radio. It’s a good idea to be checking for phase problems when recording tracks to the multitrack. Some mixers that have phase reversal switches have them operable only on the mic inputs and not on the tape inputs. Therefore, they're unavailable during mix-down.
Phase is a very important and often misunderstood factor in recording. Imagine the complete cycle of a sound wave as being like a wave in water. This wave has a crest, which pushes on your eardrum, and a trough, which pulls on your eardrum.
If two signals are electronically out of phase their waveforms can be mirror images of each other. When this happens, there can be cancellation of all or part of your sound. As the crest of waveform A pushes on your eardrum, the trough of waveform B pulls on your eardrum with the same amount of energy. This results in either no movement of the eardrum (no perceived sound) or reduced movement of the eardrum (altered, inaccurate sound).
If two waveforms are in phase, they crest and trough together. This results in a doubling of the amount of energy from that waveform, or twice the amount of air being moved.
When multiple microphones are used in the same room, sounds can reach the different mics at different times and probably at different points in the cycle of the wave. They combine at the mic out of phase. That's why it’s always best to use as few mics as possible on an instrument or group of instruments in the same. Fewer mics means fewer phase problems.
This theory also pertains to the way speakers operate. If two speakers are in phase and they both receive the identical waveform, both speaker cones move in and out at the same time. If two speakers are out of phase and if they both receive the identical waveform, one speaker cone moves in while the other speaker cone moves out. They don’t work together. They fight each other, and the combined sound they produce is not reliable.
This problem doesn’t show up as much in a stereo mix, but anytime your mix is played in mono or anytime you are combining multiple microphones to a single tape track, this can be the worst problem of all. To hear the effect of combining a sound with itself in and out of phase, listen to the guitar in the following audio examples. First, is the original track playing into one channel of the mixer. Next, the signal is split and run into another channel of the mixer. Notice the volume increase as the two channels are combined. The final example shows the sound difference as the phase is reversed on the second track. When combined, the tracks are obviously thin and reduced in level. Imagine if that happened to the guitar track in a mix as it was played on mono AM radio.
The nature of combining sounds dictates that there is always phase interaction. We wouldn’t want to hinder that because good phase interaction gives our music depth and richness. However, we do want to be particularly aware of phase interactions that can have an adverse effect on the quality of our music.
If your mixer has a phase switch on each channel, it’s probably at the top of the channel by the preamp and attenuator controls. Its purpose is to help compensate for phase interaction problems. For practical use, listen to your mixes in mono. If you notice that too many instruments get softer, disappear or just seem to sound funny in mono, then there’s probably a phase problem between some of the tracks. Change the phase of some of the tracks that might be combining in a problematic way until the mix sounds full and smooth in mono.
Short delay times, chorus and phasing effects can also cause these kinds of problems in mono, so you might also need to change some delay times to help even things out. There will be more about this when we cover mix-down. Once you’ve located and solved the phase problems, your mix will sound just as good in stereo, and you’ll be ready for television or AM radio. It’s a good idea to be checking for phase problems when recording tracks to the multitrack. Some mixers that have phase reversal switches have them operable only on the mic inputs and not on the tape inputs. Therefore, they're unavailable during mix-down.
It is impossible by the laws of physics to have phasing with only one microphone. When you use more than one microphone, it is impossible to completely get rid of phasing. If you solo two channels in mono, you will hear a noticeable reduction in bass frequencies when the signal is 180 degrees out of phase. The only way you will know is to reverse the phase of the signal. If your console doesn’t have a phase reverse button, you can build a mic cable with pins 2 and 3 reversed to accomplish the same thing. Unless the phase is reversed (180 degrees out), you'll just have to try to position your mics where they sound "good".
I always check equipment to make sure pins are wired correctly, before I hook it all up. You’d be amazed at how much stuff comes from the factory wired out of phase from the ISO standard (mics, cables, etc). Aside from signals that are 180 degrees out of phase, you just have to decide what sounds better. I sometimes use phasing on purpose. Try this:
Put 2 57’s (or whatever) on a soundsource. Set one on axis and the other at a 45 degree angle. You can print them to separate tracks or blend them at mixdown, by adjusting their relative balance. This is referred to as “phase eq”. BTW… I don’t believe in doing things like whipping out the measuring tape to set overheads. Sure that’ll get the snare in phase, but if you can’t get a good blend off the toms, or the ride sounds funny, you’re just back to square one. At the end of the day, the best results are obtained using your ears… not the metric system ;-)
Brad Gallagher
http://www.just-for-musicians.com/
I always check equipment to make sure pins are wired correctly, before I hook it all up. You’d be amazed at how much stuff comes from the factory wired out of phase from the ISO standard (mics, cables, etc). Aside from signals that are 180 degrees out of phase, you just have to decide what sounds better. I sometimes use phasing on purpose. Try this:
Put 2 57’s (or whatever) on a soundsource. Set one on axis and the other at a 45 degree angle. You can print them to separate tracks or blend them at mixdown, by adjusting their relative balance. This is referred to as “phase eq”. BTW… I don’t believe in doing things like whipping out the measuring tape to set overheads. Sure that’ll get the snare in phase, but if you can’t get a good blend off the toms, or the ride sounds funny, you’re just back to square one. At the end of the day, the best results are obtained using your ears… not the metric system ;-)
Brad Gallagher
http://www.just-for-musicians.com/
Tom Hicks
Well-known member
with both mics on the grill,it would take waves so short the dogs would howl to get into phase trouble!Seriously,the more common mistake is one mic on the grill and another on the open back of the cab.These signals will be almost exactly 180 degrees out of phase.
I was cruising the cubase web ring for plugins the other day and found a phase switch plugin.I usually monitor in mono to catch that stuff right away.
Tom
I was cruising the cubase web ring for plugins the other day and found a phase switch plugin.I usually monitor in mono to catch that stuff right away.
Tom
Scooter B
New member
RE: Phase issues/Phase cancellation.
I read a neat trick in Bassplayer Magazine on combining direct inputs and mic inputs to reduce phase cancellations. This requires the phase switch to invert the phase OR a reverse wired cable as mentioned above.
While listening to your first track input (direct input or another mic) adjust your second track input (mic input) to the distance from your sound source that causes the "Thinnest sound" this will be the point of maximum phase cancellation... now reverse the phase with your phase switch and you should have the point of minimum or no phase cancellation!
Swapping mic cables (with a reverse wired cable) could be a little tricky if your mic stand is not well secured. From what I have read the small adjustments to get to fullest bass sound (least phase cancellations) when using DI and a mic is harder to pinpoint than finding the weakest or thinnest sound and reversing it.
Also as Xtremedb stated 100% inphase at all frequencies with two mic sources is not physically possible and is sometimes used as an effect. Acoustic guitars with a piezo/bridge pick up and an external (or internal) mic will also run into this.
I read a neat trick in Bassplayer Magazine on combining direct inputs and mic inputs to reduce phase cancellations. This requires the phase switch to invert the phase OR a reverse wired cable as mentioned above.
While listening to your first track input (direct input or another mic) adjust your second track input (mic input) to the distance from your sound source that causes the "Thinnest sound" this will be the point of maximum phase cancellation... now reverse the phase with your phase switch and you should have the point of minimum or no phase cancellation!
Swapping mic cables (with a reverse wired cable) could be a little tricky if your mic stand is not well secured. From what I have read the small adjustments to get to fullest bass sound (least phase cancellations) when using DI and a mic is harder to pinpoint than finding the weakest or thinnest sound and reversing it.
Also as Xtremedb stated 100% inphase at all frequencies with two mic sources is not physically possible and is sometimes used as an effect. Acoustic guitars with a piezo/bridge pick up and an external (or internal) mic will also run into this.
sjoko2
New member
A couple of points.
Phase cancellation between two microphones capturing a same signal occurs only when the mics in question capture a wave both at the same time, but one does so with the wave on the upwards curve, the other one with the wave on the downwards curve.
You don't have to go to the extent of having out-of-phase cables, switches etc. All you need to do is look at your microphone placement. Move one of the 2 microphones away or towards the source by the length of the predominant frequency wave, and your phasing problem will be gone.
Microphone placement is the end all and be all of recording. That is where your phasing problems occur, that is where you should fix them. It is also why you hardly ever hear really well recorded drums, without phasing between, in particular, room and overhead mics.
Unless ---- sometimes its good to flip phase for effect. For example, I often have one in and one out of phase microphone top and bottem of a snare.
Now you know why you sometimes will read a note with advertisements of high end microphones saying "mixed stereo pairs available"., meaning they are capable of providing two microphones with exact the same characteristics, normally at a premium price.
Phase cancellation between two microphones capturing a same signal occurs only when the mics in question capture a wave both at the same time, but one does so with the wave on the upwards curve, the other one with the wave on the downwards curve.
You don't have to go to the extent of having out-of-phase cables, switches etc. All you need to do is look at your microphone placement. Move one of the 2 microphones away or towards the source by the length of the predominant frequency wave, and your phasing problem will be gone.
Microphone placement is the end all and be all of recording. That is where your phasing problems occur, that is where you should fix them. It is also why you hardly ever hear really well recorded drums, without phasing between, in particular, room and overhead mics.
Unless ---- sometimes its good to flip phase for effect. For example, I often have one in and one out of phase microphone top and bottem of a snare.
Now you know why you sometimes will read a note with advertisements of high end microphones saying "mixed stereo pairs available"., meaning they are capable of providing two microphones with exact the same characteristics, normally at a premium price.
Sorry, I’m not buying it. That explanation may work fine in a textbook, but in the real world, it is *never* that easy. For one thing, there are always placement constraints. On the underside of a snare, sometimes, you’re lucky to fit a mic at all, much less have the liberty to measure how far out of phase the wave is and move the mic accordingly. There are lots of similar situations where this is the case. As I mentioned in my previous post, the stuff you buy from the store will often arrive wired out of phase to begin with. Are you supposed to move the mic all over the place, just because they can’t conform to the iso standard?
If you don’t have a phase switch on your console, I admit it makes things a little tougher. If you don’t want to change cables, they build adapters, which are basically metal tubes with out of phase contacts. Just plug it in before the board and listen for the low end. That’s a hell of a lot faster than moving the mics around and guessing. Once you’re at least in the same ballpark, you can work on placement.
If the cable was wired out of phase to begin with and you move the mic to correct for this, you may create another problem. For instance, now you might now really be picking up the ride etc. Where has that gotten you? Nowhere.
BTW reversing the phase on the underside of a snare is *not* done for effect. It is simply good sound engineering. This is a common phase problem, as is reversing the phase on an open back cabinet, when using both front and back mic’ing.
Brad Gallagher
http://www.just-for-musicians.com/
If you don’t have a phase switch on your console, I admit it makes things a little tougher. If you don’t want to change cables, they build adapters, which are basically metal tubes with out of phase contacts. Just plug it in before the board and listen for the low end. That’s a hell of a lot faster than moving the mics around and guessing. Once you’re at least in the same ballpark, you can work on placement.
If the cable was wired out of phase to begin with and you move the mic to correct for this, you may create another problem. For instance, now you might now really be picking up the ride etc. Where has that gotten you? Nowhere.
BTW reversing the phase on the underside of a snare is *not* done for effect. It is simply good sound engineering. This is a common phase problem, as is reversing the phase on an open back cabinet, when using both front and back mic’ing.
Brad Gallagher
http://www.just-for-musicians.com/
Gidge
Lapdance Test Dummy
Oh, I got that book....Audio Recording for Dummies.....
Im always willing to throw my 2 cents in to help but Im always open to the idea that I could be wrong.....so when someone offers another insight on one of my posts I usually shut my mouth and open my ears cause I might just learn something.....
Especially on boards like this...hell, you never know who you are talking to...could be someone in disguise....George Massenberg, Glyn Johns,Eddie Kramer,Puff Daddy,DrDre,Mutt Lange,George Martin,Bob Ezrin,Freddie Haayen,Alan Parsons,Don Was,Desmond Child,Bob Clearmountain,Bruce Fairbairn,Ted Templeman, and the list goes on.....Would you discredit (not necessarily disagree) with one of these guys?.....
Im always willing to throw my 2 cents in to help but Im always open to the idea that I could be wrong.....so when someone offers another insight on one of my posts I usually shut my mouth and open my ears cause I might just learn something.....
Especially on boards like this...hell, you never know who you are talking to...could be someone in disguise....George Massenberg, Glyn Johns,Eddie Kramer,Puff Daddy,DrDre,Mutt Lange,George Martin,Bob Ezrin,Freddie Haayen,Alan Parsons,Don Was,Desmond Child,Bob Clearmountain,Bruce Fairbairn,Ted Templeman, and the list goes on.....Would you discredit (not necessarily disagree) with one of these guys?.....
Sorry if I came across a little harsh. I’m sure the book isn’t crap. The problem is it’s impossible to fit life experience into a book… It would be 5,000 pages long and no one would read it. I know… I’ve been working on a book for live sound and I’ve all but given up. You don’t want to leave anyone behind, but at the same time, you don’t want to bore the hell out of the rest of the people. The experience has taught me a great deal about the way I share information with other people.
My purpose for coming across strongly is to keep people from repeating mistakes I have made in the past. Does that post at least make sense to everyone? I’d hate to think everyone considers me a jerk and on top of that they aren’t learning anything from my rudeness ;-)
Brad Gallagher
http://www.just-for-musicians.com/
My purpose for coming across strongly is to keep people from repeating mistakes I have made in the past. Does that post at least make sense to everyone? I’d hate to think everyone considers me a jerk and on top of that they aren’t learning anything from my rudeness ;-)
Brad Gallagher
http://www.just-for-musicians.com/
Gidge
Lapdance Test Dummy
Aw dont worry, as long as Sonusman is around, you wont be the biggest jerk.....
But speaking of life experiences, I think Sjoko2 finished reading his dummies book and may have done a few practice projects here and there, probably nothing youve heard of though.....
http://www.ngsproductions.com/
But speaking of life experiences, I think Sjoko2 finished reading his dummies book and may have done a few practice projects here and there, probably nothing youve heard of though.....
http://www.ngsproductions.com/
sjoko2
New member
Gidge LOL anyone ever tell you that you are a mischievous little so-and-so??
Damn I've heard about all those people you mention somewhere.
What do they do? See if I can remember.
Freddie, he's from The Hague, Holland. He never finished high school, became the coffee boy at Polydor, or was it the president?
Alen, he's english right? I think he came here a couple of years ago and never left. George, an army green console with round buttons instead of faders. Good teacher. Glyn, Mutt, funny names, must have strange accents.
I'm going to read that book again just before I throw it out. You never know. And then I'm going to set up a trapset in the studio and figure out if I can fit a mic under the snare. I love a challenge!
Damn I've heard about all those people you mention somewhere.
What do they do? See if I can remember.
Freddie, he's from The Hague, Holland. He never finished high school, became the coffee boy at Polydor, or was it the president?
Alen, he's english right? I think he came here a couple of years ago and never left. George, an army green console with round buttons instead of faders. Good teacher. Glyn, Mutt, funny names, must have strange accents.
I'm going to read that book again just before I throw it out. You never know. And then I'm going to set up a trapset in the studio and figure out if I can fit a mic under the snare. I love a challenge!
Gidge… like I said, I don’t want to offend anyone. My sole objective is to share knowledge with others. I am wise enough to know that I am ignorant. However, on the points that I mentioned, I don’t believe there can be much argument. Throw names of bands at me all day long… it still won’t change the laws of physics. If I am wrong, please enlighten me. Re-read my thread and then dispute every point in it. I will objectively read it and learn from my errors.
Studio equipment is wired out of phase *all the time*. If this is where your problems lie, you should fix the problem from the source, rather than frustrate yourself running in circles. I check all of my equipment for phasing problems before I begin any project… whether it is live or recorded. That is simply smart sound engineering. I say this not to make other people look ignorant, but to help others. Nine times out of ten, when you put a second mic to pick up the sound of the snare wires, it will be out of phase. Reversing the phase of that cable is not an effect… it is simply putting that sound into its proper sonic context.
If you disagree with the points I made in my post earlier, please let me know where I was incorrect. I was under the impression that a forum was a platform for the exchange of ideas. If you feel that I was wrong in any of the statements I made earlier, please let me know. I would not want to continue misinforming the people I aim to help.
Brad Gallagher
http://www.just-for-musicians.com/
Studio equipment is wired out of phase *all the time*. If this is where your problems lie, you should fix the problem from the source, rather than frustrate yourself running in circles. I check all of my equipment for phasing problems before I begin any project… whether it is live or recorded. That is simply smart sound engineering. I say this not to make other people look ignorant, but to help others. Nine times out of ten, when you put a second mic to pick up the sound of the snare wires, it will be out of phase. Reversing the phase of that cable is not an effect… it is simply putting that sound into its proper sonic context.
If you disagree with the points I made in my post earlier, please let me know where I was incorrect. I was under the impression that a forum was a platform for the exchange of ideas. If you feel that I was wrong in any of the statements I made earlier, please let me know. I would not want to continue misinforming the people I aim to help.
Brad Gallagher
http://www.just-for-musicians.com/
Blue Bear Sound
New member
OK... let him off the hook...
Er, Brad... they're pokin' a bit of fun 'cos sjoko is a very seasoned pro.... that "book" thing was in jest....
Bruce
Er, Brad... they're pokin' a bit of fun 'cos sjoko is a very seasoned pro.... that "book" thing was in jest....
Bruce