Low pass filtered speech

Improving Low Pass Filtered Speech Intelligibility Usii Nonlinear Frequency Compression with Cepstrum and Spectral Envelope Transformation... 

Keywords— Frequency compression, spectral envelope, low pass filtered speech, speech intelligibility, h h frequency hearing loss. 

The most important control element in the glottal source is of course the rate at which the cycles occur. In Equation 11.30, this is determined by the positions oiN and N2, in Equation 11.32 by Tq, Te and 7b and in Equation 11.31 this is determined by the impulse function u n. In the last case, the glottal volume velocity function can be thought of as a low pass filtering of an impulse stream. From these expressions and empirical measurements, it is known that this low pass filter creates a roll off of about -12dB per octave. It is this, combined with the radiation effect, that gives all speech spectra their characteristic spectral slope. 

As with formant tracking, traditional pitch detection algorithms PDAs often have three stages a pre-processing stage, where for instance the speech is downsampled or low-pass filtered, a bottom up candidate finding step, and a decision making step whereby the best candidates are picked. 

We also conducted informal listening test to evaluate the speech intelligibility of the low pass filtered and frequency compressed output signal. The listening test result showed that the output speech was improved compared to the low pass filtered input signal. This result confirmed that the speech intelligibility has being improved. 

Reed, C.M., et al (1983) Discrimination of speech processed by low-pass filtering and pitch-invariant frequency lowering. J Acoust Soc. America 74(2) 409-419... 

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