Spectral modification introduced by differentiation (solid line) and by formant equalization (dashed line). z-transforms used for differentiation and for formant equalization are given in the Appendix. The figure also shows the handset “send” (dash-dot line) and “receive” (dash-triple dot line) frequency response masks for wideband telephone (TIA/EIA-920, 2002).
Average spectrum of speech babble used as masker (solid line). The babble shows a high-frequency noise floor about 25 dB below the peak at 2 kHz. Average spectra for unprocessed speech from the two talkers used in experiment 1 (dashed lines). Note that the spectrum for babble, representing masking generated locally, is band limited to 8 kHz, while spectra for the two talkers, representing speech received over a wideband telephone system, are band limited to 7 kHz.
Intelligibility (probability of a correct response) versus spectral conditioning for the average of the two talkers (AV), for the female talker (F), and for the male talker (M). UN: unprocessed. FE: formant equalization. DIFF: differentiation. Results averaged over four experimental subjects. Vertical bars give 90% confidence intervals. Babble masker at 70 dB SPL and speech at −6 dB SNR.
Listener preference for speech processed by formant equalization over unprocessed speech (dashed line), speech processed by differentiation over unprocessed speech (dash-dot line), and speech processed by formant equalization over speech processed by differentiation (solid line). Babble masker at 70 dB SPL.
Similar to Fig. 4 except that results are shown for speech rich in glides and nasals (upper panel) and for speech rich in fricatives (lower panel). Babble masker at 70 dB SPL.
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