  Stellar oscillations are key to unravelling stars' properties, such as their
mass, radius and age. Amplitudes of acoustic modes in solar-like stars are
intrinsically linked to their convective turbulent excitation source, which in
turn is influenced by magnetism. In the observations of the Sun and stars, the
amplitude of the modes is modulated following their magnetic activity cycles:
the higher the magnetic field, the lower the modes' amplitudes. When the
magnetic field is strong, it can even inhibit the acoustic modes, which are not
detected in a majority of solar-like stars presenting a strong magnetic
activity. Magnetic fields are known to freeze convection when stronger than a
critical value: an "on-off" approach is used in the literature. In this work,
we investigate the impact of magnetic fields on the stochastic excitation of
acoustic modes. First, we generalise the forced wave equation formalism,
including the effects of magnetic fields. Second, we assess how convection is
affected by magnetic fields using results from Magnetic Mixing-Length Theory.
We provide the source terms of stochastic excitation, including a new magnetic
source term and the Reynolds stresses. We provide scaling laws for the
amplitudes of the modes, taking into account both the driving and the damping.
Those scalings are based on the inverse Alfv\'en dimensionless parameter: the
damping increases with the magnetic field and reaches a saturation threshold
when the magnetic field is strong. The driving of the modes diminishes when the
magnetic field becomes stronger, the turbulent convection being weaker. As
expected from the observations, we find that a higher magnetic field diminishes
the resulting modes amplitudes. Evaluating the inverse Alfv\'en number in
stellar models provides a means to estimate the expected amplitudes of acoustic
modes in magnetic active solar-type stars.
