For measuring attenuation by the ultrasonic pulse‐echo method, a selected echo—obtained by pulse modulating a very stable CW carrier—is directly heterodyned to produce a video signal with a beat frequency of a few hertz. This signal is then sampled at the repetition rate and filtered to give a low‐frequency CW output with a signal‐to‐noise ratio some 30 dB greater than for the selected echo. Phase shift at the wave frequency produces an equal phase shift at the beat frequency, and can be measured with a phase meter. The detection system is sensitive for weak signals and is linear. Readout of amplitude and phase can be made on standard recorders. In a second arrangement, the selected echo is added algebraically to a reference signal having a slightly different frequency. with the CW beat frequency resulting processed as before. Because of the good phase stability, this method can be used at frequencies in the high megahertz range.