Comb filter effect

A

Ampguy

Member
Hi guys, I'm wondering if anyone has an answer to a problem I'm experiencing.
When playing live at fairly high volume I get a chorus phasing sound from my rig, which is afx2 into a pair of Db technology Operas, with a mono feed into the PA. The sound is horrible and annoying, I googled combined filter sounds and it pretty much sounds like that.
After a recent gig I tried to find the problem and eventually when I shut down my vocal Mike my sound instantaneously cleaned up!

How to cure this?
Would a phase reversal adapter in the paths to the Operas sort it?

Steve

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As Chris mentions, we need to know how your vocal mic is connected up but bear in mind that introducing a phase reversal to your Db's may not do the trick.

It might not be that the phases are inverted/reversed, it may actually be due to the delay in sound from your Db's reaching your vocal mic and then going through FOH as compared to other audio/signal paths. In other words it is a phase alignment issue (not sure if I explained that very well) - i.e. not 180 degress out of phase but something else...

Does the phasing change depending on the vocal mic location and orientation?

One question though... what type of vocal mic are you using and what is the polar pattern? If your Db's are within the pickup pattern of your mic then this will be a contributory factor.
 
Thanks for your time guys, vocal mike is wired to the desktop (no phase switch I'm afraid) the Operas are aimed at the back of my head and as such straight into the SM58 Beta when my head's not there!

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Shenks said:
As Chris mentions, we need to know how your vocal mic is connected up but bear in mind that introducing a phase reversal to your Db's may not do the trick.

It might not be that the phases are inverted/reversed, it may actually be due to the delay in sound from your Db's reaching your vocal mic and then going through FOH as compared to other audio/signal paths. In other words it is a phase alignment issue (not sure if I explained that very well) - i.e. not 180 degress out of phase but something else...

Does the phasing change depending on the vocal mic location and orientation?

One question though... what type of vocal mic are you using and what is the polar pattern? If your Db's are within the pickup pattern of your mic then this will be a contributory factor.
Click to expand...
It's a sweeping phase change like LFO rather than static.

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Seems ike you're playing loud and the monitors are bleeding into the SM58.
Opera's are wedges, aren't they? How about putting them on the floor before you?
Other solution would be using a gate on your mic signal, to avoid them picking up the guitar signal.
 
Try turning off the monitors and recording your vocal mic.

It might be something about the space / mic / mic channel is the culprit and the monitors are just amplifying the problem and the monitors aren't THE problem.
 
yek said:
Seems ike you're playing loud and the monitors are bleeding into the SM58.
Opera's are wedges, aren't they? How about putting them on the floor before you?
Other solution would be using a gate on your mic signal, to avoid them picking up the guitar signal.
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I'll try this in a rehearsal space, I use iem, but like to hear a backline as well just in case the iem fails.
Operas are 350 W frfr powered speakers, pretty high quality units and they sound great with the guitar on its own. However the sound is thin when in a band situation, reading threads on this forum I am lead to believe that I need to boost the midrange to compensate.

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The SM58 Beta is a supercardioid pickup pattern so that (in theory) should help reduce unwanted bleed from your monitors unless they are pointed directly at your mic. When you are next rehearsing try moving your mic position (and direction) around in relation to your monitors and as yek mentioned try placing the monitors in front of you.

Does it also happen because you are in a very live and reverberant space rather than something more acoustically attenuated? This could also worsen the problem.
 
Shenks said:
The SM58 Beta is a supercardioid pickup pattern so that (in theory) should help reduce unwanted bleed from your monitors unless they are pointed directly at your mic. When you are next rehearsing try moving your mic position (and direction) around in relation to your monitors and as yek mentioned try placing the monitors in front of you.

Does it also happen because you are in a very live and reverberant space rather than something more acoustically attenuated? This could also worsen the problem.
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I will try all of the suggestions at rehearsal next week. Maybe having the backline monitor in front of me but aimed back will help.
Problem is I also run a Roland GR55 through another Opera , so the stage will be littered with at least three wedges just for me!.
Thinking back when I first got the afx2 I used a matrix 1k power amp into a stereo 4x12 Marshall and didn't get this problem, it just didn't sound as good as the Operas do (without any phasing issues)

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Where do you have your high cut in your cab block? Could it be that it's at default 20 kHz or just to high? Did you try to lower it down to 5-6 kHz, max. 12 kHz?
 
Ampguy said:
I will try all of the suggestions at rehearsal next week. Maybe having the backline monitor in front of me but aimed back will help.
Problem is I also run a Roland GR55 through another Opera , so the stage will be littered with at least three wedges just for me!.
Thinking back when I first got the afx2 I used a matrix 1k power amp into a stereo 4x12 Marshall and didn't get this problem, it just didn't sound as good as the Operas do (without any phasing issues)

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Click to expand...

Putting the monitor in front of you will help. But in a rehearsal room or small venue podium, if you put up the volume of your monitor too loud it will happen again. Had it one time when accidentally putting up volume too high (with an FM12, and I confirm it sounds awful. It's not an Axe Fx issue therefore.
 
lauke-lux said:
Putting the monitor in front of you will help. But in a rehearsal room or small venue podium, if you put up the volume of your monitor too loud it will happen again. Had it one time when accidentally putting up volume too high (with an FM12, and I confirm it sounds awful. It's not an Axe Fx issue therefore.
Click to expand...
Thanks for the advice, I'm using more iem than loudspeaker now and the comb effect has gone. Comb effect is a horrible sound, not at all like real chorus or phaser.

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don_joe said:
Where do you have your high cut in your cab block? Could it be that it's at default 20 kHz or just to high? Did you try to lower it down to 5-6 kHz, max. 12 kHz?
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This is the correct answer! Thanks a million!

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don_joe said:
Wow, I'm glad it helped. :)
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The problem is with hifi sound coming from the backline we're fooled into thinking this sounds fantastic , but there's a lot more top and bottom than a real amp gives. This makes the guitar sound thin so we crank it up and the the comb effect occurs, thanks again for your help.[emoji4]

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Ampguy said:
The problem is with hifi sound coming from the backline we're fooled into thinking this sounds fantastic , but there's a lot more top and bottom than a real amp gives. This makes the guitar sound thin so we crank it up and the the comb effect occurs, thanks again for your help.[emoji4]

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Click to expand...
That's a good explanation. Going directly into a DAW for recording and playing live are two different worlds. It takes a while to learn to make a good live preset, it's not easy at all. It's much easier with the cleans but with gain, you can tweak for days and still not be entirely happy with it.

I've read an excellent tip recently from someone here to put the mic type in the cab block to "null" (instead of "none"), it really opens up the sound for playing live, I don't know how I missed that before. Now I'm almost there...
 
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