  We show that the generalized slow-roll approach for calculating the power
spectrum where the inflationary slow roll parameters are neither small nor
slowly varying can be readily extended to models with non-canonical kinetic
terms in the inflaton action. For example, rapid sound speed variations can
arise in DBI models with features in the warp factor leading to features in the
power spectrum. Nonetheless there remains a single source function for
deviations that is simply related to the power spectrum. Empirical constraints
on this source function can be readily interpreted in the context of features
in the inflaton potential or sound speed.
