Bob Cain writes:

Would you technical guys agree that the two tone interaction we are
hypothesizing can be approximated to low order by:

l*sin((wh+wld*sin(wl*t))*t) + h*sin((wl+whd*sin(wh*t))*t)

with h and l related to the amplitudes of the HF and LF components
respectively, wh the frequency of the HF tone, wl the frequency of the
LF tone and wld and whd a measure of the "depth" in Hz

wld and whd would be depths in radians.
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