Topic: Phasing and wind.

[KLowe]

Is it caused by the wind disrupting the pressure waves?

I have a few shows from langerado this year that sound like the cymbal crashes are "swirling" around. 

I wiki searched phasing and kindof understand it.  Does anyone have a total n00b explanation of phasing etc, etc for me to read/understand?

Thanks

-DSatz...where you at? 

[Roving Sign]

You pretty much got it!

Sound is moving air...if the air is moved by something other than sound - it will affect the sound too...

I think some directional patterns may emphasize the swirl...

Rare cases I've seen the speaker rigging sway in the wind causing a similar effect...

[Patrick]

Think about it....You have a speaker and a microphone.

  The speaker cone moves the air in front of it, and that pressure created by the speaker travels all the way back to your microphone.  When there is wind in between the speaker cone and your microphone, it will disrupt the travel of the sound pressure.  When you're running a stereo recording rig, the sound from the speakers do not hit your microphones at the same time, due to the disruption by the wind.  The left/right microphones will record the sound at different times and this is what causes unwanted phasing noises.

Any stereo pattern is going to be affected by wind, however I'm sure that certain patterns are better than others.  More coincident patterns probably handle this better.  Also, certain polar patterns handle wind noise better; Omni's and subcards perform well in the wind, while shotguns and hypers are a little more sensitive to wind noise.

Hope this helps!

[Roving Sign]

I think higher frequencies might also diffuse quicker after leaving the speaker...thus making them more susceptible to the swish...

[Church-Audio]

Is it caused by the wind disrupting the pressure waves?

I have a few shows from langerado this year that sound like the cymbal crashes are "swirling" around. 

I wiki searched phasing and kindof understand it.  Does anyone have a total n00b explanation of phasing etc, etc for me to read/understand?

Thanks

-DSatz...where you at? 

Wind has a huge effect on sound waves coming from a PA system. There is no way to avoid this its part of doing sound out doors. The louder the PA is the less likely you would hear it. But with a lower output level and a strong wind the sound wave front from the PA system gets bent. This bending causes phase distortion because it changes the arrival time of the sound and also changes the space that the sound once occupied. Its kind of like bending a note on a guitar. But the guitar is always in phase with it self because its a single note coming at you in a single direction. With a large outdoor pa its coming at you from many directions and therefor its easy to hear the phase shift especially if you can also hear the sound coming from the stage.

Chris

[Church-Audio]

I think higher frequencies might also diffuse quicker after leaving the speaker...thus making them more susceptible to the swish...

The higher the frequency the shorter the waveform the more wind can effect it. Lower frequencies tend to be stronger and more omnidirectional less susceptible to the influences of wind on there proportional characteristics.

 

[heyitsmejess]

Rare cases I've seen the speaker rigging sway in the wind causing a similar effect...

phish 9-20-00.

the stacks under the pavillion were swaying at least 4' side to side....worse storm ive ever been outdoors for.

i was in the middle of the pavillion, and STILL got wet from the rain (was blowing in from the sides).

[rocksuitcase]

Is it caused by the wind disrupting the pressure waves?

I have a few shows from langerado this year that sound like the cymbal crashes are "swirling" around. 

I wiki searched phasing and kindof understand it.  Does anyone have a total n00b explanation of phasing etc, etc for me to read/understand?

Thanks

-DSatz...where you at? 

Wind has a huge effect on sound waves coming from a PA system. There is no way to avoid this its part of doing sound out doors. The louder the PA is the less likely you would hear it. But with a lower output level and a strong wind the sound wave front from the PA system gets bent. This bending causes phase distortion because it changes the arrival time of the sound and also changes the space that the sound once occupied. Its kind of like bending a note on a guitar. But the guitar is always in phase with it self because its a single note coming at you in a single direction. With a large outdoor pa its coming at you from many directions and therefor its easy to hear the phase shift especially if you can also hear the sound coming from the stage.

Chris

Since all these explanations are fairly accurate, I will just add some scientific terms you can look up.  The acoustic effect the wind has on stereo microphonics is called "comb-filtering".  When you look it up, you will see it used in electronics design more often than in room acoustics.  BUt in room acoustics, comb filtering is the "swirl" that you are hearing in your windy recordings.  As some on else stated, it is due to the arrival of the sound waves being "pushed" or "squeezed" out of place because the wind shifts the sound pressure just enough to make the same frequency hit the mics at different arrival times.  The difference in arrival times is what people are hearing when they use the term "phasing" or "out of phase".

Bruel and Kjaer write some amazingly thorough technical literature on these things especially relating to their Dual channel FFT analyzers ( which acousticians use to analyze room acoustics)
http://www.bkhome.com/

[SmokinJoe]

This has been bugging the hell out of me too (just came back from a windy Mountain Jam).

I hypothesize that most of this occurs when the wind blows you stand so you mics are bobbing around in space like the tip of a fishing rod, then all the distances and angles are changing.  I suspect if you had you mics attached some sort of solid object it would be much less noticable.

If I'm right on this, I'm about to invest in a 20pound steel stand... from my "Strengths of Materials" class I took 20 years ago I remember that steel weighs about 3 times as much as aluminum, but you will get 1/3 the deflection too.

[taper420]

I noticed this in my mountain jam recordings too. I got rid of most of it by applying a filter called wideness, in CDSpindoctor. The wideness does just what it says. Widens the soundstage of the recording. This is presumably done by some kind of manipulation of phase over different frequencies, based on the same science as noise canceling headphones. It definitely widened the soundstage, but also had the beneficial effect of reducing the phasing issues caused by the wind. It does sound better with headphones than on a stereo though.

[danlynch]

+t and thanks for the tip 420!  This is an especially pertinent topic as the outdoor taping season approaches.

Other than the phasing, there is also the "noise" caused by the wind -- the actual force of the wind against the mics that causes level spikes.  Screens can filter this for the most part, but not completely.  Does the "wideness" manipulation have any effect on this phenomenon?

[Gutbucket]

Chris knows what he's talking about, this is one of his areas of expertice (FOH sound). I'm lead to believe the wind/air interaction itself is most of it. The comb-filtering aspects due to the stand moving and/or any mic separation contribute somewhat of course, but you can hear the same effect if you plug one ear and stand still at an outdoor show, which eliminates those variables.  There may be some comb-filtering from the two stack sources reaching your single ear at slightly varying times die to wind modulating the arrival times of the two separate sound sources (especially with a mono mix) or swinging the hanging arrays, but there is also the modulation of the sound waves themselves in the air.  My point basically is that if you had a single rigidly mounted speaker and a rigidly mounted mono mic, you'd still hear the swirly sound effect at distance with big gusty winds.

Hey Chris, you have an email from me.

[run_run_run]

lots of good stuff here, learned allot. Joe's steal stand is going to be the next big thing

[taper420]

The wideness does not get rid of wind noise... only reduces phasing issues caused by it.

In fact it may make it worse, because instead of everything being cluttered and mixed together at the center, frequencies get separated out over the soundstage, so you can hear each instrument more clearly.... which has the effect of hearing the wind more clearly. Some of this can be reduced with a low end cut, but I tend to just leave it because a low end cut will effect some quality in the bass... and I just look at it as something that comes with the experience..... just like crowd noise. If the music is loud enough, and your in a good spot, it should overpower the wind anyway. Or you could spend a few hundred on some good wind jammers, or choose sub-card/omnis when it's really windy.

FWIW CDspindoctor is an accessory program for Toast, available for the mac. Anybody know of similar features or plug-ins for other software?

[Church-Audio]

Chris knows what he's talking about, this is one of his areas of expertice (FOH sound). I'm lead to believe the wind/air interaction itself is most of it. The comb-filtering aspects due to the stand moving and/or any mic separation contribute somewhat of course, but you can hear the same effect if you plug one ear and stand still at an outdoor show, which eliminates those variables.  There may be some comb-filtering from the two stack sources reaching your single ear at slightly varying times die to wind modulating the arrival times of the two separate sound sources (especially with a mono mix) or swinging the hanging arrays, but there is also the modulation of the sound waves themselves in the air.  My point basically is that if you had a single rigidly mounted speaker and a rigidly mounted mono mic, you'd still hear the swirly sound effect at distance with big gusty winds.

Hey Chris, you have an email from me.

Humm wonder how they came up with the Lesley speaker

[Gutbucket]

...My point basically is that if you had a single rigidly mounted speaker and a rigidly mounted mono mic, you'd still hear the swirly sound effect at distance with big gusty winds.

Humm wonder how they came up with the Lesley speaker

Yeah! Do the opposite and get some super-cool swirlyness by not rigidly mounting the speaker but spinning it around on purpose. 

Back in my Beetle-infused 4-track cassette days I once set up 4 mics and the batt powered cassette recorder on one of those old playground push merry-go-rounds with the mics along the edge, one at each quadrant, recorder at the center, everything taped down good to stay put.  We'd spin the thing and our four piece band would play, one of us on each side, for a crazy psychedelic effect. 

[KLowe]

The wideness does not get rid of wind noise... only reduces phasing issues caused by it.

In fact it may make it worse, because instead of everything being cluttered and mixed together at the center, frequencies get separated out over the soundstage, so you can hear each instrument more clearly.... which has the effect of hearing the wind more clearly. Some of this can be reduced with a low end cut, but I tend to just leave it because a low end cut will effect some quality in the bass... and I just look at it as something that comes with the experience..... just like crowd noise. If the music is loud enough, and your in a good spot, it should overpower the wind anyway. Or you could spend a few hundred on some good wind jammers, or choose sub-card/omnis when it's really windy.

FWIW CDspindoctor is an accessory program for Toast, available for the mac. Anybody know of similar features or plug-ins for other software?

so.  would panning "wide" with a normal pan function do the same thing?

[SparkE!]

Here' my attempt at boiling it down into the bare essentials:

Sound travels in air at some well-defined velocity (which is constant throughout the listening space) that depends on atmospheric pressure and temperature.  When you add wind to the situtation, sound still travels at the same velocity relative to the air, but the wind is moving the air so the actual velocity that the sound travels is that of speed of sound plus the local speed of the wind (which probably is not constant throughout the listening space).  If sound travels by two paths, one of which is assisted by the wind and the other of which is not as assisted by the wind, and they recombine elsewhere with one of them arriving a half wavelength sooner, then they will recombine destructively and the combined volume will be reduced.  When the wind changes and doesn't give the wind assisted path that extra 1/2 wavelength of extra distance traveled, then sound arriving through those two paths recombines constructively and the combined volume will be increased.

Boiled down even further:  Wind simply blows the air around while it carries sound on its way to your ears. The resulting sound that you hear gets to your ears by different paths each time the wind changes.

Boiled down even further: Wind blows the sound around and makes it sound all swirly.

[danlynch]

FWIW CDspindoctor is an accessory program for Toast, available for the mac. Anybody know of similar features or plug-ins for other software?

Soundforge has an application called "pan/expand".

[Gutbucket]

Excellent boil, Spark.

[spyder9]

I noticed this in my mountain jam recordings too. I got rid of most of it by applying a filter called wideness, in CDSpindoctor. The wideness does just what it says. Widens the soundstage of the recording. This is presumably done by some kind of manipulation of phase over different frequencies, based on the same science as noise canceling headphones. It definitely widened the soundstage, but also had the beneficial effect of reducing the phasing issues caused by the wind. It does sound better with headphones than on a stereo though.

Under Adobe Audtion 3.0, its under:

Effects > Filter and EQ > FFT Filter Process > Mastering Heavy and Wide

+T on this find.  Made a big difference.  Thanks!   

[mblindsey]

While I've been unsuccessful in using it for wind blown recordings with phase issues, there is a very cool stereo plugin called 'JS:StereoField' in the uber-cheap DAW, Reaper (http://www.reaper.fm/).  The DAW and the "rotate stereo this-way, that-way" plugin are very cool.  There are a ton of other handy plugins too.  It's hard to beat for $50.  I use it for most of my *.wav operations these days....

--Michael