Characteristic Maximum-Length Sequences for the Interleaved Sampling Method

摘要

Since the introduction of the maximum-length sequences (MLS, also M-sequences) measuring technology by Schroeder (Schroeder, 1979) and his collaborator (Alrutz and Schroeder, 1983) into acoustics, a number of theoretical and experimental research works on binary MLS for acoustic measurements have frequently been reported about, amongst others in (Borish and Angell, 1983; Chu, 1990; Xiang, 1992). The advanced MLS measuring technology is based on a fast algorithm first termed by Conn and Lempel (Cohn and Lempel, 1977) as fast M-sequences transform (FMT). In a recent research note (Mommertz and Bayer, 1995) Mommeitz and Bayer described an efficient technique using an interleaved sampling method to extend the frequency limit given by the A/D-converter of PC-based systems. They exploit the decimation property of binary MLS (see Golomb, 1967, page 78) which facilitates the interleaved sampling. A binary MLS of D periods is applied to a system under test in terms of D-times interleaved sampling, resulting in one period of same MLS (apart from a phase shift), where D is a decimation (interleave) factor. D must not have a common (prime) divider with the length L of the MLS, D should be at least in form of 2* with A; being a positive integer (see also Golomb, 1967). Applications of the interleaved MLS can be found in a wide range (Mommertz and Bayer, 1995), for instance, room-acoustic scale modelling and ultrasonic measurements where the maximum sampling frequency of the A/D-converter is undesirably limited by the state of art of current PC-based systems.