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The aim of the study was to discover whether there are perceptual constancies between classes of complex sounds, even though the acoustic information is very different. Listeners were asked to identify sounds consisting of vowels, musical instrument tones and meaningless buzz sounds, presented at three different fundamental frequencies (octave shifts), and at three signal-to-noise differentials. The sounds were numbered but not named. The vowels had voice-like quality in mid-octave (110 Hz); the musical tones sounded music-like at the highest octave (220 Hz); at the lowest octave (55 Hz) both music and vowels were physically meaningless; the meaningless buzz sounds had no greater relevance in one octave than any other. These buzz sounds could be distinguished from each other by differing harmonic patterns. It was found that, in the absence of masking noise, the vowels were better identified in mid-octave than were the musical and meaningless sounds. The musical sounds were not better identified than the others in high octave. The meaningless sounds were unexpectedly easier to identify in the low octave. They generally withstood thermal noise masking well, but not buzz masking, compared with the musical and vowel sounds. It was more difficult to identify musical and vowel sounds during thermal noise masking than during buzz masking. It would seem the fixed-ratio hypothesis is not applicable to vowel (formant) sounds within the octaves tested. It may be used, however, to explain the constancy of identification for sounds which depend on harmonic patterning.