A review of results on frequency shifts and vowel identification
Peter F. Assmann, Terrance M. Nearey · Canadian acoustics · 2003
Recent studies have shown that speech remains intelligible when the spectrum envelope was shifted up or down along the frequency scale across a fairly wide range. However, intelligibility decline when the shift factor was greater than about 1.5, or less than 0.7. This paper presents evidence from a perceptual experiment and describes a model of vowel identification that accounts for the effects of frequency shifts in terms of listeners' sensitivity to statistical regularities in natural speech.