An ultrasonic inspection system utilizes a tunable digital filter with 4× interpolation. The system is used for scanning objects to be tested and includes a transmit/receive device to generate a test signal and receive an echo signal. A signal processing circuit processes the echo signal with one or more digital to analog converters for converting an analog version of the echo signal to a digital echo signal in the form of streaming digital data which is stored in a memory. The data is stored at a first data rate and read out at the second, slower data rate. An averaging decimator receives and processes the data from the memory and supplies it to an IIR filter and subsequently to an FIR filter and ultimately to a box car filter to effect processing thereon which increases the perceived resolution of the data by a given factor, preferably by a factor of 4.