a,b) Spectrograms of example sounds from the vocalization (Mexican hairy porcupine, human, and common nightingale) and ambient noise ensembles (wind, vacuum cleaner, rain), with the AMs in nightingale song and rain in the frequency band around 6.5 KHz shown below. c,d) The amplitude distributions of the AMs in the sounds shown in a and b in the carrier frequency band around 6.5 KHz. Colors correspond to the boxes in the upper righthand corner of the spectrograms in a and b. AMs were normalized to have a minimum amplitude of 0 and a maximum amplitude of 1. e,f) The power spectra of the AMs in the sounds shown in a and b in the carrier frequency band around 6.5 KHz, with the gray band denoting the 20–120 Hz frequency range. AMs were normalized as in c and d. g) The parameter values that provided the optimal fits for the average amplitude distribution of the AMs in each sound ensemble for a range of carrier frequencies (exponential distribution for vocalizations, Rayleigh distribution for ambient noises). Each sound ensemble was divided into 10 segments, and the error bars in panel g denote one standard deviation of the distribution of optimal parameter values across these segments. h) The value of *α* that provided the best fit of the function 1/*f*^{α} to the average power spectra of the AMs in each sound ensemble in the 20–120 Hz frequency range for a range of carrier frequencies.

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