Help me understand phase problems?

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moffdnb
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2006/07/21 11:36:45 (permalink)

Help me understand phase problems?

Folks,

Hope you can shed some light here. I got a little plug-in that renders a stereo signal to "mono" beneath a chosen freq. I have tested it out on a final mix by "mono-izing" the signal below 250hz and leaving the above freq untouched and in full stereo.

What I have noticed is that my bassline & Kick drum drops very low and both are struggling to be heard within the mix. I also lost some of there seperation.

Would I be correct in assuming this is what "Phase problems" are? If so how can I resolve the issue or at least try and avoid it in future?


Thanks for your time,
Ste
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    Clydewinder
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    RE: Help me understand phase problems? 2006/07/21 11:48:56 (permalink)
    it means the waveforms in your left and right channels are opposite, i.e. when you add them together you get zero or something close to it. if you render to a stereo file and zoom WAY in you can see one channel's waveform goes UP DOWN UP DOWN and the other one goes DOWN UP DOWN UP. it affects all frequency ranges but is sometimes more noticeable in low frequencies because the longer waves can partially cancel out without totally annihilating each other.

    if you are using some STEREOIZING or CHORUS effects on bass guitar or kick drum then sometimes when they sum back to mono this problem presents it self. many stereo wideners are notorious for this problem which is why they are not often used. sounds great in headphones but in a room the bass just nulls itself out.

    The Poodle Chews It.


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    moffdnb
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    RE: Help me understand phase problems? 2006/07/21 13:56:58 (permalink)
    Well explained mate! Appreciated!


    How can I avoid this problem though? I may want to have everything under 250hz in mono as I sometimes make DnB which benefits from this.

    But if I render any of the bass sounds I use (Access virus B synth) I'm gonna have this trouble?
    #3
    tcbetka
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    RE: Help me understand phase problems? 2006/07/21 14:10:22 (permalink)
    There's a great book out there called "Modern Recording Techniques," and they have a website with tutorials:

    http://www.modrec.com/tutorials.html

    Check out the one on "Phase". You can download a .wav file and pop it into Sonar to view the waveforms. You just zoom way in on the tracks and see the actual (pure) wave. You can notice the phase relationships of the waveforms in the adjacent tracks, and this helps reinforce whats going on. Finally, just solo the tracks alone or in combination to hear the actual difference. Basically, two tones exactly in phase are twice as loud as one; and two tracks exactly (180 degrees) out of phase results in silence.

    Check it out--once you do you'll never wonder about phasing again.

    They have a lot of other neat tutorials as well; all are described in the text but are free to download and pretty self-explanatory, so you don't absolutely need the book. But it's a great book.

    TB

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    #4
    Slugbaby
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    RE: Help me understand phase problems? 2006/07/21 14:15:20 (permalink)
    I have a bass guitar that seems to do that exact thing.
    If I turn up both pickups 100%, the volume slightly drops. Is this probably caused by phasing too?

    (sorry for the tangent!)

    http://www.MattSwiftMusic.com
     
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    #5
    moffdnb
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    RE: Help me understand phase problems? 2006/07/21 14:36:27 (permalink)
    Thanks folks for your input but erm... how do I avoid this in my mizes if I'm dead set on a particular sound (that will suffer phase problems if I mono it?
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    Phrauge
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    RE: Help me understand phase problems? 2006/07/21 14:39:54 (permalink)
    Move the clip slightly. HTH.
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    Clydewinder
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    RE: Help me understand phase problems? 2006/07/21 14:45:16 (permalink)
    sometimes a synth will add a chorus or widener effect to "beef" up the sounds... if possible bypass any effects that run inside the synth or just record one side of the output. if you have 2 mono tracks you can flip the phase of one of them and see if that helps. or as phrauge said slide one clip over slightly so the waveforms are complimentary instead of opposite. if you have already recorded a interleaved stereo track you would need to split it into L & R tracks first.

    The Poodle Chews It.


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    tunekicker
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    RE: Help me understand phase problems? 2006/07/21 15:06:16 (permalink)
    Another way to "avoid" this is to start your mixes in Mono. It's easier to hear where instruments are fighting with each other this way, and you can make sure the Mono mix sounds good. Makes you feel really good when you take a rough guess at panning and make the switch to Stereo.

    It might also be possible that the plug you're using isn't the best. When checking phase with drum overheads and deciding when to hit the Polarity switch, the bass frequencies are where you notice it the most. The closer the signals are to being in phase, the fuller the bass frequencies will sound. It might be worth investigating whether your plugin is "linear phase" or not (it may have an option for linear phase operation, too.)

    Time (phase) and frequency are mathematically linked to each other, so it takes a lot of calculation to mess with one and not screw up the other. If you happen to have downloaded PlParEQ3 from Refined Audiometrics while it was free, it has an M/S mode that is linear phase, and works really well for the sort of work you're trying to do. You might try downloading the trial of PlParEQ here and messing around with the M+ S- setting under the M/S column. It's a $1000 plugin you can demo with no strings attached for 30 days!

    Peace,

    - Tunes
    #9
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