September 22, 2006
Looking at the Wah-wah Effect on the Middle A on the Alto Kalimba

The middle A note (right side middle colored tine) has the most pronounced wah-wah effect on the ALTO kalimba, so we'll start by examining it. This is what the A sounds like when I do a wah-wah, starting closed, then opening: hear wah-wah.

And this is what that note looks like:

First comes the note's attack, then number 1 refers to the first closed phase (i.e., my thumb and fingers are covering the sound holes), number 2 refers to the first open phase, number 3 refers to the second closed phase, and number 4 refers to the second closed phase. On the recording, there are a few more closed and opens, but they are low enough amplitude that you can't see them on the plot.

We now examine the spectrum (i.e., which notes are present) in each of those four regimes.

Shown above is the spectrum of number 1, the first closed phase. Last week we discovered that when we play a note on the side, the other tines that are right next to it also will ring, but they will skip the notes in between which are on the other side of the kalimba. We have a fair amount of B, D, and F#, and significantly more A (the note I actually plucked), then fair amounts of C, E, and G. That A is an overtone, as it is above the highest note on the kalimba.

Shown above is the spectrum of number 2, the first open phase. Compared to the spectrum for number 1, we see there is a lot less B and D, the same amount of F#, way much more A, a bit more C, and less E, G, and the overtone A. Also, there is much less power in the very high frequency overtones.

The spectrum of number 3, the second closed phase, shows the A amplitude is way down, and with it the amplitude of the neightboring tines, F# and C, also went way down. high E and G are way down, as well as all overtones. But D is up.

In number 4, the second open phase, D goes way down, F#, C, and E are about the same, and A is way up - not as high up as it was in the first open phase.

So, what is going on?

For one, as time goes on, the amplitude of the vibrations gets generally weaker, so we need to be aware of that. But when we do a wah-wah, we are making a see-saw in the spectral domain. When we cover the holes, D gets stronger and A gets weaker. When we open the holes, A gets stronger and D gets weaker. We are taking some of that vibrational energy in one note and putting into the other note, back and forth as we cover and uncover the holes.

Next week, we'll take a close-up look at what the low D note does when we do a "wah-wah".