New Interpretation of the Stereophonic Effect in Lauridsen's and Similar Binaural Experiments

Abstract

In 1954, H. Lauridsen reported an experiment which gave a remarkable stereophonic effect using a single input signal. The signal was fed to both ears once directly in phase and a second time (delayed by 50–150 milli-seconds) in antiphase. In a recent paper [Akust. Beib. 6, 482–488 (1956)], G. R. Schodder gave an explanation of the resulting stereophonic effect which is based on the analogy between Lauridsen's (and similar) experiments and hearing conditions in rooms. In this paper a different interpretation will be offered. These experiments are recognized as resulting in two different intensity-versus-frequency responses in the paths to the two earn (two interlaced comb-filters in Lauridsen's case). The presence of such different (but indiscriminable by the ear) intensity-versus-frequency responses is postulated as the essential prerequisite that stereophonic effects be obtained from a single input signal. This theory accounts for most of the observed phenomena which could not or not easily be explained by Schodder's interpretation such as his own observation of a strong effect at very high frequencies. To further support this view a number of differential filtering experiments have been conducted. A magnetic tape recording demonstrating some of the results will be played. An earlier view held by this author, namely, that all that is needed to produce a stereophonic effect are two physically different wave forms which would sound alike individually, could not be sustained. Several experiments with pairs of all-pass filters having different phase-versus-frequency characteristics did not give the strong stereophonic illusion observed with differential intensity filtering.