In this video I want to talk about how to identify a comb filter
and I think the two easiest ways are number one just to look for regular
peaks and dips and number two just move the microphone. So let's walk
through this together. What is a comb filter? Comb filter is just a series of
regular peaks and dips and so to the untrained eye this might look a look
like a pretty strange looking comb, right? These are all different sizes, but
if I press option T to open my transfer function options and I change this graph
setting from a frequency scale of one third octave to linear aha now the
regularity of those peaks and dips is a lot more clear now this looks like a
comb okay so this is where the term comb filter comes from is looking at the
series of peaks and dips on a linear scale which we almost never do right but
that's where the term comes from so are you going to switch your graph to linear
mode to be able to identify this every time you need to do this probably not
what you are gonna do though is you're going to be looking for this pattern of
regularity so not only can I see this in the amplitude but I also see some
regular things happening weird things happening here in the face in the same
thing in the coherence display here right coherence goes to crap coherence
goes the crap coherence goes to crap okay these all these three things are
lining up to tell us this is probably a comb filter there's some reflection
happening here there's something happening in the air over here that I
can't really I shouldn't try to do anything with my EQ I shouldn't try to
fix acoustical problems with electrical solutions
okay so the second thing I mentioned was just moving the microphone right so I'm
gonna leave this on linear for now so this will be really obvious I'm gonna
turn the measurement back on and I'm gonna move the microphone over a little
bit
you
all right that's interesting right I move the microphone over four or five
inches and all of a sudden our dips are peaks and our Peaks are dips so so this
is the second indication for me that I've got a comb filter everything
changes when I move the microphone over a little bit just to be sure let's move
it one more time
you
all right again our Peaks have shifted around a little bit right and now
they're not so bad this time I move the microphone away from the wall so the
distance from the peaks and dips have shrunk a little bit and they're in
slightly different places again okay so let me change this back by the way so
you can see change this back to 1/3 octave
okay so the practice here is to be able to with our normal 1/3 octave display
here be able to identify this regular series and just to recap the way I do
that is by looking for these regular series of peaks and dips and also if I
just move the microphone a little bit does the whole thing change and that's
how you identify a cone filter now in the next video let's talk about how to
avoid a queuing a cone filter sound design