Singing return loss is the return loss in the bands of frequencies both below and above the ERL (echo return loss) band. The bands Lo and Hi, measured separately, give an indication of the system's tendency to oscillate or "sing". SRL-Lo is measured like ERL, except the energy resides mainly in the band from 260 to 500 hertz. SRL-Hi is a counterpart to SRL-Lo in the 2200 to 2400 hertz band.

Test sets for measuring ERL, SRL-Lo and SRL-Hi are more complex than single frequency bridges due to the noise shaping circuits employed, but they provide with a single number a more comprehensive return loss measurement. See Figure 1.