Photometric amplitude ratios as indicators of companion stars. First three panels from left to right: photometric-to-RV amplitude ratios from Gaia DR3 and VELOCE against the logarithmic pulsation period, with wavelength of the photometric band increasing from left to right. Right panel: ratio of Gaia photometric amplitudes in G_Bp to G_Rp. Filled circles show SB1 Cepheids reported in VELOCE. Other single-mode Cepheids observed by VELOCE are shown as open circles. There is no clear difference between SB1 Cepheids and all others in any of the amplitudes considered, nor a dependence of such a difference on log P_puls.