11.   Above this frequency, the attenuation ceases to be negligible and the phase shift ceases to be sufficiently proportional to frequency.

12.   Positive feedback between the open-loop output and noninverting input is provided by the Wien band-pass filter comprising components C and R.

13.   Such positive feedback can occur because the original design was not sufficiently careful or because of additional phase shifts that could not reasonably be foreseen.

14.   Recall that parasitic oscillation takes place if the magnitude of the loop gain is greater than or equal to unity at the frequency at which the phase shift becomes.

15.   The secret is phase shift, a technique that electronically enhances the spatial separation of sounds. . . .