  Spectro-temporal processing is essential in reaching ultimate per-photon
information capacity in optical communication and metrology. In contrast to the
spatial domain, complex multimode processing in the time-frequency domain is
however challenging. Here we propose a protocol for spectrum-to-position
conversion using spatial spin wave modulation technique in gradient echo
quantum memory. This way we link the two domains and allow the processing to be
performed purely on the spatial modes using conventional optics. We present the
characterization of our interface as well as the frequency estimation
uncertainty discussion including the comparison with Cram\'er-Rao bound. The
experimental results are backed up by numerical numerical simulations. The
measurements were performed on a single-photon level demonstrating low added
noise and proving applicability in a photon-starved regime. Our results hold
prospects for ultra-precise spectroscopy and present an opportunity to enhance
many protocols in quantum and classical communication, sensing, and computing.
