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Phase continuum

Discussion in 'Recording' started by jm2, Oct 28, 2008.

  1. jm2

    jm2 Active Member

    I often read about the importance of having tracks or mics in phase, however, what I have never seen discussed is the degree of shall we say in-phaseness. In fact, it is possible that two tracks could exist such that they are neither in phase nor out of phase. Could we call this state phaseless? :wink:

    How much deviation is acceptable?

    If one is a novice, and does not trust thier ears, what is a simple way to determine if two mics are adequately in phase?

    Can phasing issues manifest if a single guitar is recorded by one mic and one direct signal from a pick up?
     
  2. BobRogers

    BobRogers Well-Known Member

    In theory, a phase shift can (and usually does) occur any time the same sound is recorded by two signal paths. A phase shift is simply a time delay between the two signals. You can see it by zooming in on the time domain and comparing two recordings of the same sound. Two signals are rarely perfectly in sync (this is a good thing) but the time shift is usually so small that you don't get any cancellation - where the peaks of one signal align with the troughs of the other.

    Short story is you pretty much have to use your ears. No good way to objectively measure all of the variables and put a number on the effect. It's a complicated subject, and there is no way to explain every detail in a short post. Try to look up details on subjects like phase cancellation and comb filtering.
     
  3. RemyRAD

    RemyRAD Guest

    Basically a recording is a serious combination of different phase distortions over periods of time & space. That is modern-day recordings, recorded with multiple microphones.

    However there is a criteria for establishing whether one microphones is "out of phase"to another. Of course you have the ability with the PAN POT to position each microphone anywhere within the left & right. So, with the microphones in their individual tracks left & right, it may sound great and ultra wide. Then you would take your pan control and turn them both to center. If the microphones are in phase, you should hear a buildup of the signal and plenty of low frequencies. If on the other hand the microphones are out of phase, it will appear lower level, thin sounding and the bass may nearly disappear as it cancels out. So on a lot of our consoles & monitoring systems, you'll find a "mono" button. A convenient way to collapse the stereo mix to mono. It's not really there to enjoy the mix in mono but to check the mix in mono. So usually cancellation of low frequencies indicates you're either out of phase or within a distance ratio of less than 6 feet from each other. At that stage, things are neither in phase nor out of phase but maybe having other frequency phase cancellation issues which causes a clouded sound.

    There are some of us who utilize purposeful phase inversion to specifically cause cancellation or to correct for polarity issues. Such as when you put a microphone on the top of the snare drum. And one on the bottom of the snare drum. You want to invert the phase of the one on the bottom. If it isn't in phase that will make it very thin sounding. If you invert the phase on the bottom microphone, it will correct the polarity in relationship to the top microphone and you'll suddenly get a big fat smackin' snare drum. When I put a bass drum microphone into the bass drum, sometimes I invert phase. And that is to specifically cause certain frequencies to cancel with respect to the overhead microphone pickup. It can give you a tighter sounding less flabby drum set sound. Along with making the bass drum sound much more present & harder hitting. Less flabby. Tastes great. Less filling. Tastes great.

    Now some microphones seem to appear to neither be in phase nor out of phase. I find that most ribbon microphones are at a 90° or 270° phase difference from dynamics or condensers. If microphones are far enough away from each other, phase isn't an issue and time delay is. At some large room studios that might have a 60 foot diameter. The time delay between instruments on each side can be excessive. Anything over 20 ms is completely obnoxious and sounds out of timing. That is unless you want that kind of effect? Think Led Zeppelin. Great drum sound with a couple of microphones 30 feet down the hall and around the corner. And everybody just keeps wondering how he got that sound. Now, it was all the microphones on the drums and the pair that was more than 30 feet away. So everybody needs to put their Mike's on the drums 30 feet away. And just one overhead on the drums at close in.

    So fat bass = in phase.
    Anemic bass = out of phase.

    Remy Ann David= rarely phased
     
  4. jm2

    jm2 Active Member

    Thanks for the replies. My version of Cubase (LE4) does not have a mono switch, but I can obviously pan to the center.

    So, if I my take on the responses is correct, there is a bit of lattitude in phase relationships, and one can achieve acceptable results by getting close to in phase.
     
  5. Clowd

    Clowd Guest

    No worries, just create a mono output bus and only use it when you want to check.
     

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