This paper describes a technique for the measurement of sound velocities to pressures of 100 kbar, utilizing ultrasonic pulse techniques in which variations in transit time together with independent measurements of sample length changes are taken into account. This arrangement permits measurements to be made through and above transformations in samples under pressure and frees the apparatus from stringent parallelism requirements applicable to other interferometry techniques. The accuracy of the velocity measurements at high pressure is 1%. Results obtained in this system on gold are in good agreement with predictions based on low pressure single crystal measurements.