The speech scale
Srinivasan Umesh, Leon W. Cohen, D.J. Nelson · Acoustics Research Letters Online · 2002
We report experimental results indicating a universal commonality among speakers when enunciating phonetically similar sounds. Using real speech data, we have numerically computed a frequency-warping function, such that in the warped domain, spectra from different speakers are similar except for a translation factor. We refer to this frequency-warping function as the “speech scale.”