I shall present the current state of modelling pulsation amplitude ratios between intensity and radial velocity of radial pulsations in the Sun and in other main-sequence stars. The importance of comparing observed, contemporaneous, measurements of photometric and spectroscopic amplitudes of stochastically driven pulsations with model computations is discussed, with emphasis on understanding the physics of the near-surface layers in main-sequence stars. Additional to the amplitude ratios, also the phases between temperature and velocity perturbations can be compared, which put further constraints on our stellar models. The SONG network, together with the recently launched TESS mission, will be capable of providing unprecedented and high-quality measurements of amplitudes and phase shifts.