 |
A more extreme effect used with distorted electric guitars is amplifier feedback. In this case, the amplified guitar waveforms couple back to the strings with some gain and delay, as depicted schematically in Fig.9.4 [492].
The Amplifier Feedback Delay in the figure can be adjusted to
emphasize certain partial overtones over others. If the loop gain,
controllable via the Amplifier Feedback Gain, is greater than 1 at any
frequency, a sustained ``feedback howl'' will be
produced. Note that in commercial devices, the Pre-distortion gain
and Post-distortion gain are frequency-dependent, i.e., they are
implemented as pre- and post-equalizers (typically only a few
bands, such as three). Another simple choice is an integrator
for the pre-distortion gain, and a differentiator
for the post-distortion gain.
Faust software implementing electric-guitar amplifier feedback may be found in [456].
