AFS Wizard
Dr. J
Posts: 209
This topic was sort of talked about in another thread where Dra was explaning to a guy how he uses the "Speech" filter and then a couple of the other "Fixed" & "Live" filters in the AFS. I use the AFS before every show (Monitors and FOH) and it seems to do a decent job but I thought I would bring up some observations and maybe get some others in on the discussion. First, I will list from the manual the "Types" of filters you can use:
Apparently these types refer to the "Q"
1. Speech - Bandwidth = 1/5 octave & Q= 7.25
2. Music Low - Bandwidth = 1/10 octave & Q= 14.5
3. Music medium- Bandwidth = 1/20 octave & Q= 29
4. Music High - Bandwidth = 1/80 octave & Q= 116
I set my filters @ "Music High" 6 Fixed and 6 Live BUT I still get feedback at times. Now I can use something with a smaller "Q" or I could actually use more Fixed than live filters but I was wondering what you all use to handle this? What is the Q on a 1/3 octave GEQ? Dra - you probably know this. The Q has to be pretty low in comparison to some of these others and just by doing the math in my head it would probably be somewhere around a Q of 4. I feel that using the Music High is almost too specific (1/80 octave & a Q of 116! Sheesh) because there are so many right by it. For example: Running the feedback wizard while having Smaart up and running -- the first feedback is at 3.57k (For my system), the second one is at 3.??, the third one is at 4.?? then 6.75K... it just keeps going but if we grab a 3.15k & 4K on the GEQ it gets rid of it in a hurry but then we lose some of the life out of the system. I know Dennis uses Smaart along with his GEQ and does just fine. Maybe the cuts on the GEQ don't have to be major cuts. Anyway -- I just brought this topic up because I noticed the "Q" settings the wizard uses and wanted to know what the 1/3 octave GEQ "Q" was just to show in the comparison. It seems that the "Speech" or even "Music Low" would be pretty decent if a guy was gonna use the AFS. It is still much narrower of a bandwidth than a GEQ. I got to find a way to use as little as possible or my sound guy (father-in-law) will get on the GEQ and cut it to death!
Apparently these types refer to the "Q"
1. Speech - Bandwidth = 1/5 octave & Q= 7.25
2. Music Low - Bandwidth = 1/10 octave & Q= 14.5
3. Music medium- Bandwidth = 1/20 octave & Q= 29
4. Music High - Bandwidth = 1/80 octave & Q= 116
I set my filters @ "Music High" 6 Fixed and 6 Live BUT I still get feedback at times. Now I can use something with a smaller "Q" or I could actually use more Fixed than live filters but I was wondering what you all use to handle this? What is the Q on a 1/3 octave GEQ? Dra - you probably know this. The Q has to be pretty low in comparison to some of these others and just by doing the math in my head it would probably be somewhere around a Q of 4. I feel that using the Music High is almost too specific (1/80 octave & a Q of 116! Sheesh) because there are so many right by it. For example: Running the feedback wizard while having Smaart up and running -- the first feedback is at 3.57k (For my system), the second one is at 3.??, the third one is at 4.?? then 6.75K... it just keeps going but if we grab a 3.15k & 4K on the GEQ it gets rid of it in a hurry but then we lose some of the life out of the system. I know Dennis uses Smaart along with his GEQ and does just fine. Maybe the cuts on the GEQ don't have to be major cuts. Anyway -- I just brought this topic up because I noticed the "Q" settings the wizard uses and wanted to know what the 1/3 octave GEQ "Q" was just to show in the comparison. It seems that the "Speech" or even "Music Low" would be pretty decent if a guy was gonna use the AFS. It is still much narrower of a bandwidth than a GEQ. I got to find a way to use as little as possible or my sound guy (father-in-law) will get on the GEQ and cut it to death!
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Comments
You are correct that if your speakers have a peak bell that covers 4k - 6k that is +4db, you could have feed back at 4k. An EQ can get that freq reasonably well, but in doing so affects 1/3 of an octive with a reverse bell. It will pull from about 3.5k to 4.5k. 1 octive is "do, ra, me, fa, so, la, te, do". If feedback is at "fa", a 31 band (or 28) will also affect 1/2 of "me" and 1/2 of "so". And that is if the feedback is right on top of ISO center. On center you might only need a 3db cut, but if the feedback occurs half way between "fa" and "so" then you may have to pull 6db from one or the other, or 3db from both to get the "edge" of the bell to reach over and fix it.
In the driverack you get 28 shots at hitting the the feedback dead on, and what's the odds of that. Even then it is 1/3 of an octive. With AFS you get parts of a hertz as the center, so you don't alter "me" or "so" when "fa" feeds back. So even at 1/5 (speech) there is a 50% improvement over the GEQ. 300% (M-low), 600% (M-med), 2400% (M-hi).
Having said that, if the number of fixed filters still give feedback, you have 2 options...
increase the # of fixed, or
step down a Q level.
I usually start at MH. If that doesn't work, try MM, and so on. The most important thing is to do a flattening session and permanately fixed your speakers with the PEQ's, then the QEG and AFS are used soley to work on room resonances.
Not sure if that helps or if that is what you were after.
DRA
PS - Oh! I forgot. Since the first feedbacks are the most excitable, I will mix-n-match filters, starting wider and working narrower. On the 260 you can see the freq and the grouping. On the DRPA you can't, but if you could see them and your are using 4 filters on Music-High, all really close to each other, then clearing and starting over with a single wider filter. Then you can go back to the more narrow ones and more filters available. Listen closer to the squeals and if they sound really similar....
DRA
Maybe Gadget can get Mike to clear some of this up.
DRA
http://www.sengpielaudio.com/calculator-bandwidth.htm
I guess a 1/3 octave would have a "Q" of 4.32