The Modulation Transfer Function for Speech Intelligibility
Figure 1
Component spectrotemporal modulations make up the modulation spectrum.
(A) Spectrogram of a control condition sentence, “The radio was playing too loudly,” reveals the acoustic complexity of speech (Audio S1). All supporting sound files have been compressed as .mp3 files for the purpose of publication; original .wav files were used as stimuli. (B) Example spectrotemporal modulation patterns circled in the sentence (A) can be described as a time-varying weighted sum of component modulations. (C) The MPS shows the spectral and temporal modulation power in 100 sentences. The outer, middle, and inner black contour lines delineate the modulations contained in 95%, 90%, and 85% of the modulation power, respectively. Down-sweeps in frequency appear in the right quadrant, whereas upward drifts in frequency are in the left quadrant. Slower temporal changes lie near zero on the axis, while faster changes result in higher temporal modulations towards the left and right of the graph.