  It has been established in Schwarzschild spacetime (and more generally in
Kerr spacetime) that pairs of geometrically different timelike geodesics with
the same radial and azimuthal frequencies exist in the strong field regime. The
occurrence of this socalled isofrequency pairing is of relevance in view of
gravitational-wave observations. In this paper we generalize the results on
isofrequency pairing in two directions. Firstly, we allow for a (positive)
cosmological constant, i.e., we replace the Schwarzschild spacetime with the
Schwarzschild-de Sitter spacetime. Secondly, we consider not only spinless
test-particles (i.e., timelike geodesics) but also test-particles with spin. In
the latter case we restrict to the case that the motion is in the equatorial
plane with the spin perpendicular to this plane. We find that the cosmological
constant as well as the spin have distinct impacts on the description of bound
motion in the frequency domain.
