[Harp-L] Wahs of sorts

["Jonathan R. Ross" <jross38@xxxxxxxxxxx>]

A pure volume pedal is fairly easy to find.  Here are a few:

http://www.zzounds.com/cat--Guitar-Volume-Pedals--2636

I've never used one so can't comment on these particular ones.

But, to the much more interesting subject of wah, in all its various
states.  First off, let's discuss what "wah" actually is.  Whether it be
a "wah-wah" pedal or an "auto-wah" device, what is "wah" is actually a
filter-based effect.  You are sending the signal through a filter and
sweeping that filter's frequency up or down.  Now, to understand that,
you need to know what a filter is, what the various types do and what it
means to change the frequency of a filter as well as what resonance is
in terms of filters.  

In the field of electronic musical devices, a filter does what it's name
implies: it filters out certain frequencies from the signal sent through
it.  There are two primary types: low-pass, which only lets the signals
below the set frequency go through (pass); high-pass, which only lets
the signals below the determined frequency through.  By combining these
in various ways you can get other, more complex types of filters:
band-pass, which lets a select set of frequencies around the determined
frequency through; notch-pass, which is the reverse of band-pass,
letting a certain amount of high and low frequencies through; comb
filter, a very complex type which is used in making phasers, choruses
and such.

All this time I've been talking about setting a frequency.  Wah-wah
pedals use the pedal to set the frequency, and when you move the pedal
up and down you are changing what frequencies are being let through, you
are controlling the frequency manually (pedally, in this instant, but
the idea is the same).  The other way is to use a modifier of some sort
sending a control signal which changes the frequency for you.  The main
modifiers used for filter frequency are envelope generators.  These can
be thought of as sending a signal which electronically sweeps the
filter's frequency up or down according to the voltage being sent--the
signal is doing what your foot does on the wah-wah pedal.  Most
auto-wahs use a type of envelope generator called an "envelope
follower", which creates an electronic signal corresponding to the
volume of the incoming signal (there are pitch-followers, but these are
a different beast than auto-wahs).  Play louder and the filter is opened
up (more frequencies get through) softer and it closes or vice-versa.
Thus the auto-wah responds to you're playing in a more nuanced manner,
while the wah-wah pedal is more directly controlled--it is similar to
conscious and subconscious thought in many ways.

Now, another factor in a filter is what is called resonance.  This is
how much the signal is strengthened (via a form of feedback) around the
set frequency.  A large resonance adds harmonics to the incoming signal,
and indeed many filters can be set into oscillation via resonance, at
which point they are actually generating a sound themselves.  Usually,
though resonance settings are lower and tend to be audible as forms of
squeekiness in a way (it's hard to describe, easy to demonstrate)--high
resonance can easily kill speakers.  Most wah devices tend to change the
resonance level along with the frequency.  This is doable in most
resonant filter designs because you can set the resonance level via an
amplitude type control.  Besides all this, there is also the question of
the filter's slope.  This relates to how sharp the cut-off of
frequencies is.  On a filter with a soft slope (traditionally expressed
in "poles", such as a 2-pole filter which has a soft slope or a 4-pole
filter with a hard slope) the frequencies which are being filter are not
immediately stopped, but seep through to a degree.  A filter with a hard
slope cuts off the frequencies in a much more definite manner, creating
a sharper sounding filter effect.  I think most wahs are 2-pole designs,
but I'm not sure.

So, what does all this have to do with harmonica?  Simple, we're talking
about filtering out frequencies from the original signal.  The richer
the harmonic content of the signal the more noticeable the filter effect
will be.  A signal high in harmonic content such as a fed-back laden
guitar or a saw-wave on a synthesizer will undergo a very noticeable
change tonally when swept by a filter.  A signal with a low harmonic
content will have a much more subtle effect.  Thus, if you feed a
sine-wave (with no harmonics, theoretically) into a filter you don't
really get much of a change from what you had before.  The harmonica,
even the amplified Chicago type sound has a fairly low harmonic content,
thus wah effects tend to be somewhat disappointing if you're expecting
guitar-type results (for some reason harmonica players often seem to
think their instrument will behave in similar ways to guitars, despite
the fact that the two have next to nothing in common in terms of the
creation of their sound).

I like wah effects, and like Richard tend to prefer auto-wahs, though I
use pedals as well.  I don't have any dedicated auto-wahs or wah-wah
pedals (I don't need such, as my modular synthesizer can do the trick
and then some), but when I use the effect I tend to add a little
something extra in to increase the harmonic content of the harmonica
signal.  Running the harp through a ring-modulator is a nice way to
spice things up, as you can mix the affected and unaffected signals to
emphasize the harmonica's original signal while adding in enough extra
harmonics to make the filter effect stand out.  A phaser can be another
way of doing this, though they tend to be more subtle.  Distortion tends
not to work as well on harmonica signals, but there are exceptions (I've
got some digital/analog distortion hybrid types which can really make
weird things happen) and I'd recommend experimenting with these to add
content to the original signal to better enable the filter effect.
Chorus and flanger pedals can also work well for fattening up the signal
before going into a filter--again, I like to mix in a bit of the chorus
or flange with more of the original signal to emphasize the harmonica
aspect of things, but that's when I'm being conservative--sometimes I
prefer to basically abandon the original harmonica signal as much as
possible into the sea of effects, thus creating a sort of hybrid
harmonica-controlled electronic sound.

Hope this helps.




 oo    JR "Bulldogge" Ross
()()   & Snuffy, too:)
`--'