  We study corrections to the power spectra of curvature and tensor
perturbations and the tensor-to-scalar ratio in single field slow roll
inflation due to initial conditions imprinted by a fast-roll stage prior to
slow roll. For a wide range of initial inflaton kinetic energy, this stage
lasts only a few e-folds and merges smoothly with slow-roll leading to
non-Bunch-Davies initial conditions for modes that exit the Hubble radius
during slow roll. We describe a program that yields the dynamics in the
fast-roll stage while matching to the slow roll stage independent of the
inflationary potentials. Corrections to the power spectra are encoded in a
transfer function $\mathcal{T}_\alpha(k)$. We obtain $\mathcal{T}_\alpha(k)$ to
leading order in a Born approximation valid for modes of observational
relevance today. A fit yields $\mathcal{T}_\alpha(k) =1+
A_{\alpha}k^{-p}\cos[2\pi \omega k/H_{sr}+\varphi_\alpha]$, with $1.5 \lesssim
p \lesssim 2$, $\omega \simeq 1$ and $H_{sr}$ the Hubble scale during slow roll
inflation, where curvature and tensor perturbations feature the same $p,\omega$
for a wide range of initial conditions. These corrections lead to both a
suppression of the quadrupole and oscillatory features in both $P_R(k)$ and
$r(k_0)$ with a period of the order of the Hubble scale during slow roll
inflation. The results are independent of the specific inflationary potentials,
depending solely on the ratio of kinetic to potential energy $\kappa$ and the
slow roll parameters to leading order. For a wide range of $\kappa$ and the
values of $\epsilon_V;\eta_V$ corresponding to the upper bounds from Planck, we
find that the low quadrupole is consistent with the results from Planck, and
the oscillations in $r(k_0)$ could be observable if the modes corresponding to
the quadrupole and the pivot scale crossed the Hubble radius a few e-folds
after the onset of slow roll.
