Characteristic strain of EMRIs as a function of the observed frequency. The black line is the LISA sensitivity curve (T. Robson et al. 2019) and the colored lines present contours of the observed source numbers, between 1 and 10⁵, in a logarithmic frequency bin. The dashed lines present an analytical estimation at z ≪ 1 (Equation (40)), scaling as f ^1/60 at low frequencies and f ^−19/60 at high frequencies. The color bar presents the source-frame SMBH mass that corresponds to the average redshift of the observed sources. The purple dotted line depicts the average SMBH mass M _〈z〉 = 10⁵ M _⊙.