  Gravitational wave timbre, the relative amplitude and phase of the different
harmonics, can change due to interactions with low-mass halos. We focus on
binaries in the LISA range and find that the integrated lens effect of cold
dark matter structures can be used to probe the existence of $M_{\rm v}\lesssim
10\, M_{\odot}$ halos if a single binary with eccentricity $e=0.3-0.6$ is
detected with a signal-to-noise ratio $100-10^4$.
