  We describe application of a state-of-the art digital FPGA based Lock-In
amplifier to measurements of ultrasound propagation and attenuation at fixed
frequency in low temperatures and in high static magnetic fields. Our
implementation significantly simplifies electronics required for high
resolution measurements, allows to record the full echo train in single
measurement and extract changes in both phase and amplitude of an arbitrary
number of echa as a function of an external control parameter. The system is
simple in operation requiring very little prior knowledge of electrical
engineering and can bring the technique to a broad range of solid state physics
laboratories. We have tested our setup measuring the magneto-acoustic quantum
oscillations in the Weyl semimetal NbP. The results are directly compared with
previous results obtained using standard instrumentation.
