  It has become increasingly important to include one or more individual
flavours of dynamical fermion in lattice QCD simulations. This is due in part
to the advent of QCD+QED calculations, where isospin symmetry breaking means
that the up, down, and strange quarks must be treated separately. These
single-flavour pseudofermions are typically implemented as rational
approximations to the inverse of the fermion matrix, using the technique known
as Rational Hybrid Monte Carlo (RHMC). Over the years, a wide range of methods
have been developed for accelerating simulations of two degenerate flavours of
pseudofermion, while there are comparatively fewer such techniques for
single-flavour pseudofermions. Here, we investigate two different filtering
methods that can be applied to RHMC for simulating single-flavour
pseudofermions, namely polynomial filtering (PF-RHMC), and filtering via
truncations of the ordered product (tRHMC). A novel integration step-size
tuning technique based on the characteristic scale is also introduced. Studies
are performed on two different lattice volumes, demonstrating that one can
achieve significant reductions in the computational cost of single-flavour
simulations with these filtering techniques.
