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Phase cancellation

Discussion in 'Recording' started by gtarist3587, Jan 23, 2005.

  1. gtarist3587

    gtarist3587 Guest

    What are phase problems/cancellation? I haveh eard about it being when two or more mics are "out of phase". i would love to know what this is/how to fix it/how to tell if it's happening. thanks.
  2. gtarist3587

    gtarist3587 Guest

    Can anybody help me out on this? please
  3. DaveRunyan

    DaveRunyan Active Member

    Dec 13, 2004
  4. Roey

    Roey Guest

    When two identical signals are delayed in relation to one another, and then summed - some frequencies might cancel.

    So if two mics are not at the same distance from the source (let us say a snare), such a phenomenon might occur when the two mics are mixed. It can be recognised in various ways - drop in level, 'phasing sound', loss of frequencies etc.

    You can try it out yourself: take one channel and duplicate it, make sure both channels are panned to the centre, then nudge the duplicate by 3ms, and again and again and again... You should hear the sound changing in more than one way.
  5. Dave62

    Dave62 Guest

    For a more extreme example duplicate and invert an audio region in your daw and put both regions at the start of the timeline. When panned left and right it will sound odd, and if you pan them both center, all sound output should stop (100% cancellation) yet the track meters in your daw will show signal. Nudge it only 1 sample and you will start to hear the material. Real world drum recording phase issues can be done with your ears but is far easier with a daw and a stick klik. Line up all mics before the session and put them in record and make a loud noise. Then inspect them in your daw, the initial wavefront should all point the same way (usually up), if not invert the phase on the standout mikes. Older EV mics (308 etc.) were built out of phase when compared to Sennheiser and Shure and one nevers knows when a cable has had pin 2&3 crossed so you have to check. Hope this helps
  6. jdsdj98

    jdsdj98 Active Member

    Jun 8, 2002
    Denver, CO
    There are lots of ways to describe and demonstrate the symptoms of phase issues. In fact, you'll probably get a different answer/explanation from each person that responds here.

    My girlfriend moved recently. When she hooked up her stereo, she connected one of her speakers backward. She had no idea what I was talking about when I tried to explain what she had done. So, improvising in the moment, I made her sit down between the speakers and told her to close her eyes. I played an acoustic guitar track and, while her eyes were closed, told her to point to the guitar. She couldn't do it. 'Cause in an out of phase (180 degrees, the symptom of a backward wired speaker) stereo field, all sense of sonic placement is destroyed. Once that point was made, I reversed (corrected) the speaker connection and repeated the test, and she immediately pointed dead center. I gave her a cookie. True story. She understood phase.

    Do this test with your home stereo, or your studio setup. I'm assuming that you currently have your speakers correctly wired. Red connects to red. Black connects to black. Simply reverse those connections on one end of one of the speaker wires. Listen carefully to what you hear. Attempt to locate specific instruments sonically. You will have trouble doing so. If you hear the same things happening in a correctly wired environment, you have a 180 degree phase shift (cancellation) somewhere.

    This is simply the most drastic, the most obvious, the easiest to hear, phase shift/phase problem. The trick for you will be to learn to hear less dramatic phase issues and identify them as problems, and learn how to address them. The easiest way to describe a slight phase shift (problem) is to say that it will sound like a source is coming at your ears through a tube, or a tunnel. Vague description, I know, but it becomes easier to hear the more you learn what to listen for.

    Phase problems are, generally speaking, a result of one of two things being wrong:

    1. time relationships
    2. electrical flow

    Start with the test above. It's a great basic start to understanding how to hear phase problems. Also, understand that the concept of phase is what allows us to sonically locate objects/events in the real world. If you're standing on a street corner tomorrow, and step off the curb, a car coming from your left will honk its horn. You will immediately turn your head and look to the left because your left ear heard that horn slightly before your right ear, because the car is closer to your left ear than the right. Your brain recognized that, and the difference in the time that your left and right ears heard the horn is referred to as phase. You can understand how important these concepts and considerations are when approached from an audio or recording standpoint. Think about microphone placement when using 2 or more microphones on a single source. Lots to consider.

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