  Band calculations on HgBa$_2$CuO$_4$ and La$_{(2-x)}$Sr$_x$CuO$_4$ with
phonon and spin-waves within the CuO planes show that partial gaps are created
at various energies depending on wavelengths. Spin and phonon gaps appear at
different energies when the modulations are along [1,1,0], while they are at
the same energy for modulations along [1,0,0].
  It is shown that the ability to form gaps and antiferromagnetic waves is
correlated with the strength of the interaction parameter $\lambda_{sf}$ for
spin fluctuations. Many unusual properties of the high-T$_C$ oxides can be
understood from spin-phonon coupling.
