The effect of amplitude modulation on the structure of the acoustic signal spectrum in marmots [Effet de la modulation d'amplitude sur la structure du spectre du signal acoustique des marmottes].

Résumé

The amplitude modulation (AM) is a temporal change in the signal. The relationship between the AM and the spectrum of the sounds produced is exemplified by the alarm call of three marmot species (Marmota sibirica, M. menzbieri, M. caudata). In the case of AM higher and lower than the carrier frequency (F0) side frequencies are formed (F0 ± ΩI, i = 1, 2, 3...). In signals devoid of AM, side frequencies are absent. In case AM is present only in some part of the signal, the side frequencies, too, are only present in that part of the signal. The interspecies frequency distinctions are accordingly accompanied by interspecies distinctions of the carrier frequency in relation to the modulating oscillation frequency, F0 / Ω. That ratio in M. sibirica is 10 in M. menzbier 18, in M. caudata 34. The lower frequency of the modulating oscillation, the signal spectrum of M. caudata has a greater number of side frequencies. The modulating oscillation is almost periodic. In all cases, the frequencies of the modulating oscillation higher than 1 (Ω2,Ω3...) were almost divisible to the first-order frequency (Ω1). In the signals of M. sibirica and M. caudata the ratio of Ω2, 3.../ Ω1 differed the integer by 0.02-0.08. In the signal of M. menzbier it differed by 0.21-0.25. It is not yet clear whether AM ensures adaptive advantages for the marmots. Potentially, it opens up great opportunities for increase in the jam resistance of the message being transmitted and information encoding, as is the case in radio-engineering.