Taperssection.com
Gear / Technical Help => Ask The Tapers => Topic started by: blu666z on January 20, 2004, 06:08:00 PM
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Can someone explain phase shifting to me? I may be using the wrong term, but I am listening to DMB 07.02.97 @ Red Rocks and sounds like the sound source moves around occasionally.
-Kevin
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Great question!! Happens on outdoor tapes esp. big festivals. I'm not sure if that is the right term but I have my ideas. I will stay tuned for a wise one's answer....Is this from the wind moving the PA speakers when they are hanging fro the stage rigging
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It's caused by the wind "shifting" soundwaves in the air. Has a bigger effect on the higher frequencies and seems to cause losses in detail, namely in something like a cymbal crashing. Listening through headphones you can notice it significantly...sounds like the sounds are moving between channels.
My best explaination, if some one has something more scientific, please do post....
:twocents:
RR is a venue that would definately produce this more commonly.
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same sound waves out of phase will cancel each other out. results in loss of certain frequencies - mostly affects the highs. caused by improper mic configurations (too much or too little spacing) and by environmental factors such as wind and air temp (both can interfere with the speed of the sound wave).
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It's caused by the wind "shifting" soundwaves in the air. Has a bigger effect on the higher frequencies and seems to cause losses in detail, namely in something like a cymbal crashing. Listening through headphones you can notice it significantly...sounds like the sounds are moving between channels.
My best explaination, if some one has something more scientific, please do post....
:twocents:
RR is a venue that would definately produce this more commonly.
.....my physics memories aren't that great, but i believe it has something to do with sound waves traveling though a moving fluid (air) affecting the higher frequencies which are more directional than low freq. maybe it's somehow related to Doppler's effect?????
if the PAs are moving, you will hear the same pitch but with phase shift, you actually hear a difference in pitch.
sorry i couldn't explain it better.
marc
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Thanks guys. Any info was more than I had to being with. +Ts all around.
-Kevin
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Red Rocks tapes can sound real bad since it is a venue that is at the base of the foothills which often have strong winds. When there is no wind, the results are amazing though!
There are some omni sources that sound amazing and do not have any major phase shifting from the wind. Omni's at RR are generally not a good idea though since the seating area is sloped rather steeply for an outdoor venue.
Phase shifting is really a difference in the sound waves arriving at different, or unexpected, times, in this case from the wind. Professionally, phasing is looked at how equally the sounds come from or play out of a system.
This is about Phase Shifting: http://www.espace-cubase.org/anglais/page.php?page=level1pp1
Here is a link on digital phasing, which isn't on par, but the phase idea is right on: http://www.earlevel.com/Digital%20Audio/Phase.html
Unfortunately, our hobby is generally overlooked for examples of the differences in time in which the sound waves arrive.
Phil
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why dont we hear this while we are in the venu? why is it only on tape?
is there a optimal config for windy situations?
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why dont we hear this while we are in the venu? why is it only on tape?
is there a optimal config for windy situations?
I hear it at shows all the time (outdoor of course).. it can be really distracting.
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why dont we hear this while we are in the venu? why is it only on tape?
is there a optimal config for windy situations?
I hear it at shows all the time (outdoor of course).. it can be really distracting.
Oh yeah you can hear it at the concert. ;)
It is very noticable on cymbals.
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you can definitely hear it at RedRocks while at the show
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i remember hearing somewhere that this can be corrected in wavelab somehow, but it has to be done on the fly. anyone know how this is done?
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im not sure if this a correctable problem, i know for certain that phase shifting is due to the wind moving direction frequencie's around and in some respects can be minimized by a nice and beefy windscreen, this is why at almost any outdoor festival, tapers are running large windscreens to eliminate or severely minize phase shifting, now rodrocks can be overpowering, and sometimes phase shifting cannot be minized. also there has to be a pretty significant wind to be audible to the human, i.e. why alot of redrocks tapes have these problems
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im not sure if this a correctable problem, i know for certain that phase shifting is due to the wind moving direction frequencie's around and in some respects can be minimized by a nice and beefy windscreen, this is why at almost any outdoor festival, tapers are running large windscreens to eliminate or severely minize phase shifting, now rodrocks can be overpowering, and sometimes phase shifting cannot be minized. also there has to be a pretty significant wind to be audible to the human, i.e. why alot of redrocks tapes have these problems
The only thing windscreens will limit is rumbling noise from the wind. Phase shifting will still be present regardless of windscreen size when using directional mics....
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i remember hearing somewhere that this can be corrected in wavelab somehow, but it has to be done on the fly. anyone know how this is done?
someone on here was convinced that they could effect phase by adjusting volume in wavelab or some such nonsense. Jason B and I spent an afternoon and explained how this was not possible.
so no, you are pretty much stuck with it and windscreens won't help at all with phase shifting.
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i guess i got a lilttle mixed up, yeah, reduce rumble, not phase shifting, thanks fella's
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theres really no way to fix a phase problem, unless youre some sort of magician and you can set up anohter phase, shifting the waves back into position, but that would be impossible...the phase sound is from sound waves of the same frequency and pitch being delayed and knocked out of whack somehow, whether it be wind or an electrical thing, but the phase you hear is the waves themselves not matching up totally. say this is sound. there are three waves of this specific one (usually a lot lot more)
\/\/\/\/\/\/\
\/\/\/\/\/\/\
\/\/\/\/\/\/\
------------>
that is the standard sound right there, where all the waves match up. its moving left to right
now heres a phasularly(made that one up) shifted sound
\/\/\/\/\/\/\
|\/\/\/\/\/\/\
\/\/\/\/\/\/\
------------->
the middle wave doesnt match the others, bringing more high end to some parts, and more low to others. if you were to figure out some way to phase the other two waves without touching the middle one, it would be fixed, but ive never heard of anything like that ever happening...
|\/\/\/\/\/\/\
|\/\/\/\/\/\/\
|\/\/\/\/\/\/\
------------->
but if you do put a phase on top of another, it sounds pretty sweet. mu-tron made a guitar pedal called the bi-phase which ran two on top of eachother. billy corgan used it a bit...sounded sweet if you want it, but it wouldnt do anything for a show. sorry bud, theres nothing you can do
:shocking: b
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havent been in many windy situations I guess.
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why dont we hear this while we are in the venu? why is it only on tape?
is there a optimal config for windy situations?
I have definitely heard it at the Gorge - especially up on the hill.
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ah, b and the magician method... i should try that sometime
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armen - "ah, b and the magician method... i should try that sometime"
mike - "+T Borf,......
Loudest statement ever?"
yep, when something comes along that i actually know about, i gotta run with it, guys
+Ts back
:shocking: b
edit: double quotes are tough :-\
second edit: wow...really tough - i think i got it this time though
triple edit: no...maybe now, without all the technical crap
quadruple edit: i think this is a record...screw the code quotes
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A lot of FOB stealth tapes have phase shifting on them. Especially at the wild concerts where you get caught up in the crowd swaying back and forth and your there with your expensive rig trying to lay the tracks down without getting killed. You gotta love the FOBr's who will take the risk to bring a Tool or the likes show back for us to enjoy!
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A lot of FOB stealth tapes have phase shifting on them. Especially at the wild concerts where you get caught up in the crowd swaying back and forth
Heh, my Primus Chicago recording has some phase shifting in a couple places as I got bumped back from the growing mosh pit.
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and if your interested why this hapens to the high freq's more than low it is becasue low frequencies are a lot stronger. The actual waveforms are larger and they are not effected by the wind. The higher freq's have shorter waveforms that are more suseptable to being "pushed" by the wind.
I would bet that THIS type os phase problem CANNOT be fixed in post, or with gear in line at the recording.
By the way, this is the same reason why you can hear low freq's coming from a car with bass from far away, or if you have a stereo on in another room and close the door, it rolls off all the high end info (can't make it through the door)
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and if your interested why this hapens to the high freq's more than low it is becasue low frequencies are a lot stronger. The actual waveforms are larger and they are not effected by the wind. The higher freq's have shorter waveforms that are more suseptable to being "pushed" by the wind.
I would bet that THIS type os phase problem CANNOT be fixed in post, or with gear in line at the recording.
By the way, this is the same reason why you can hear low freq's coming from a car with bass from far away, or if you have a stereo on in another room and close the door, it rolls off all the high end info (can't make it through the door)
Also, if the mics move whilst recording you will hear a change in Phase relationship, because the diaphrams are now receiving the info slightly differently, the more directional the mic the more you would notice this.
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Cleantone, I don't think that explanation is exactly right. What do you mean by stronger? Assuming equal power (SPL), a higher frequency wave has more energy than a lower one.
As far as phase shifting goes, you are right that the wavelength matters. However, it is because the distance between any two peaks in a higher-frequency wave is less than those of a lower-frequency wave. This means it takes less of a shift to be audible. If you have a 40 Hz wave and a 4000 Hz wave each shifted by the same amount of time, the 4000 Hz wave will be much more out of phase than the 40 Hz wave.
I hope that was easy enough to follow.
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MattD,
I was merely pointing out that lower frequencies have more "force" so to speak. They move further without being disrupted. That is also PART of why only the upper freqs get "phasey" in some of these recording situations.
I do grasp your shifting explanation and agree fully.
The bottom line for this thread is that there is not too much to be done to solve it once it's recorded to 2 track.
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why dont we hear this while we are in the venu? why is it only on tape?
is there a optimal config for windy situations?
Yes there is, XY.
Coincident mic configurations will have zero time arrival differences between the two capsules, which I believe should theoretically eliminate phase shifting.
Happy taping,
Ben
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That would eliminate phase differences between mics, but not phase shifting between source and mics in an outdoor venue.