Impulse response measurement using Golay codes

This paper describes a digital processing technique for measuring the impulse response of a system. The method utilizes "complementary" codes as described by Golay in 1961 and has been employed by designers of radar, communications and other equipment. This paper discusses the implementation of the technique in a device that measures the impulse response of audio bandwidth systems. The paper begins by describing the general problem of impulse response measurement using digital methods. This leads to a "unit pulse" response sequence that completely characterizes a bandlimited, linear and time-invariant system. Next, Schroeder\´s (1979) method of probing the system with pseudo-random noise and correlating the result to obtain an estimate of this response is discussed. Our method is a variation on this scheme wherein the system is probed twice using sequences chosen from among the Golay codes. These codes have the remarkable property that their autocorrelation functions have complementary side-lobes. Finally, the response of a speaker/microphone pair is measured using the proposed method.