This describes how the frequency response of a guitar pickup to an individual string can be modified by a process I call "shading".
Sometimes the top string of a guitar such as a stratocaster can be too shrill or lack the meat desired for certain types of music. Turning down the tone control corrects this but at the expense of the desired edge on the tone of the rest of the strings.
A low pass filter just for the one pole can be constructed by shading the pole with a copper shim placed between it and the strings. The impedance of the pickup and its basic response are barely affected by this. The diagram below shows the effect of a 0.8mm copper shim. It represents the difference between the unshaded and shaded responses. The effect is as a low pass filter with -3dB just below 2kHz.
Note how the phase shift starts to return to zero at high frequencies. This is because, with this particular setup, the attenuation bottoms out at -12dB. The shim is thinner than the maximum pole projection on a staggered pole pickup and so doesn't interfere with picking.
© 2020 Arthur M Quinn
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