PubMed · 5952456
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M Lawrence. 1966-06-06. How we hear.. https://doi.org/10.1001/jama.196.10.931
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Digital filters with conventional lowpass, highpass, bandpass, and band reject frequency response curves are perfectly adequate for many research applications in speech and hearing. However, there are some specialized applications for which these conventional response characteristics are less than ideal. In this paper we describe a simple method for generating digital filters with virtually any amplitude and phase response. The process involves (a) calculating the impulse response of a finite impulse response filter from a text file that specifies the desired magnitude and phase response of the filter, and (b) convolving the impulse response with the input signal. Sample applications of this method are described.
OBJECTIVE: The development of a test of virtual speech intelligibility in noise that enables assessment in typical, everyday listening situations. To eliminate extraneous confounding factors, digital signal processing was incorporated to simulate listening environments and source locations and allow presentation of stimuli via earphones. DESIGN: Source-to-eardrum transfer functions measured on KEMAR for various source locations in anechoic and reverberant environments were used to process monosyllabic words and speech-spectrum noise. Speech intelligibility was measured for three speech and noise configurations in two environments using an adaptive procedure to determine the signal-to-noise (S/N) ratio for 50% intelligibility. RESULTS: Normal-hearing listeners achieved 50% intelligibility of monosyllabic words at significantly lower S/N ratios in a virtual anechoic environment than in a virtual reverberant environment. Speech intelligibility improved significantly in both environments when the speech and noise sources were separated, but the intelligibility gain in the anechoic environment was four times larger than in the reverberant environment. CONCLUSIONS: This test is easy to administer and score, and it provides a means for measuring: 1) the effects of separating speech and noise sources and 2) the effects of reverberation on speech intelligibility in noise while eliminating confounding factors such as calibration.
Speech spectra and Speech Intelligibility Index (SII) transfer functions are presented for the Swedish PB word material (SPB) and for a Swedish sentence material known as Hagerman's Sentences (HS). The transfer function were derived from the normative recognition scores in noise previously obtained from normal-hearing subjects. The transfer function for HS is very similar to a transfer function for familiar English sentences. The function for SPB is more like functions of other monosyllabic word test materials. The slope of the HS transfer function is twice as steep as the slope of the SPB function. The long-term rms spectra of the speech materials and their associated noise signals are presented and recommended to facilitate accurate SII calculations with these speech tests.