  We study the generation and propagation of gravitational waves in
scalar-tensor gravity using numerical relativity simulations of scalar field
collapses beyond spherical symmetry. This allows us to compare the tensor and
additional massive scalar waves that are excited. As shown in previous work in
spherical symmetry, massive propagating scalar waves decay faster than 1/r and
disperse, resulting in an inverse chirp. These effects obscure the ringdown in
any extracted signal by mixing it with the transient responses of the collapse
during propagation. In this paper we present a simple method to rewind the
extracted signals to horizon formation, which allows us to clearly identify the
ringdown phase and extract the amplitudes of the scalar quasinormal modes,
quantifying their excitation in strong gravity events and verifying the
frequencies to perturbative calculations. The effects studied are relevant to
any theories in which the propagating waves have a dispersion relation,
including the tensor case.
