Detection of random amplitude modulation

The main objective of this study was to determine the detection thresholds of random amplitude modulation (RAM) as a function of modulation and carrie r frequency (f(c)). The RAM was obtained by amplitude modulation (AM) of pu re-tone carriers by specially generated sample functions (modulators). The experiment concerned the detection thresholds of AM stimuli for random ampl itude changes at constant modulation frequency (f(m)) and simultaneous rand om changes in amplitude and modulation frequency. The data showed that, the detection thresholds for random amplitude modulation at constant modulatio n frequency [RAM(f(m) const)] tend to be, in a limited range of f(m), 8-14 dB lower than those for sinusoidal amplitude modulation (SAM). The detectio n thresholds for random amplitude and modulation frequency [RAM(f(m) random )] were 3-6 dB lower than the RAM(f(m) const) thresholds for high f(c) and f(m). An analysis of the responses of a set of bandpass filters (channels) stimulated by the RAM and SAM signals showed that for the middle and high c arrier frequencies, there was a good correspondence between the responses o f a set of bandpass filters used and the RAM and SAM detection thresholds.