Re:[Harp-L] Low and High Pass Filter to fight feeback?

[Richard Hunter <turtlehill@xxxxxxxxxxxxx>]

Mike Fugazzi wrote:
<Anyone ever use these?  If so, at what frequencies?  I am assuming a
<decent amount of bass and high end feedback rings at frequencies that
<actually don't matter to the sound of the harmonica.  In otherwords,
<when played, the harmonica doesn't even reach that low or high of a
<sound.

"Filter" is another name for "EQ."  A low pass filter cuts out frequencies ABOVE a certain point (thus allowing  low frequencies to "pass" through), a high pass filter cuts out frequencies BELOW a certain point.

Harmonica puts out a LOT of energy in the frequencies from 8 kHz and up, and it's usually useful to cut those frequencies back with whatever EQ you've got in order to reduce high-frequency content that will make the audience's ears bleed, even if the mic isn't feeding back.  (I have killed a lot of small animals in my time with high notes that were well below the feedback threshhold.)  But if you're using a bullet mic and a tube amp, you don't need to worry about it, because a bullet mic and tube amp combo produces a very steep dropoff in energy after 6 kHz. 

Below 100 hZ, most harmonicas are putting out breathing noise and not much else.  However, cutting EQ at 100 hZ on a typical mixer may also reduce surrounding frequencies in the 200-250 hZ range that contribute a lot to the tone of an amped harp.  

Another poster wrote that he gets feedback issues mostly at 800 hZ, and that makes sense to me.  When I check the tones I get from my Digitech amp modelers on a frequency analyzer, I see a LOT of energy in the 600-1000 hZ range.  It's easier to deal with that kind of thing with a graphic EQ, as opposed to a high or low pass filter.  I suppose you could use a band pass filter (an EQ that reduces frequencies on either side of a specific range), but why bother?  You'll sound like you're playing through a telephone, which is cool sometimes but far from always, and most feedback tends to originate in very specific, relatively narrow frequency bands, which is exactly the problem that a graphic EQ addresses.

Regards, Richard Hunter




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