1. A physiologically motivated gammachirp auditory filterbank Toshio Irino (NTT Communication Sciences. Lab. Japan) Masashi Unoki (CNBH, Univ. Cambridge/JAIST) Roy D. Patterson (CNBH, Univ. Cambridge) Sept. 2000 – August 2001

2. Early History Human Masking Data Roex filterGammachirp filter Schofield and Cooke, 1985 Irino and Patterson, 1997 Mag. Spectrum Gammatone AF Well-defined impulse response

3. Recent Developments (1) Physiological Data de Boer and de Jongh (1978) de Boer and Nuttall (1997) Gammachirp Gamma tone chirp

4. Recent Developments (2) Chirp in Carney’s Revcor data (1999) »level-independent Chirp in BMM observed post-mortem at high SPL (Recio et al. 1998). »chirp is a property of passive BM response Compressive gain in membrane motion »also in human masking data »on frequency but not off frequency Disp. Input Level Compressive

5. Chirp in Revcor data (Carney et al., 1999) Zero crossings chirp Not level dependent Noise Level Waveform Instant. Freq.

6. Where is level dependency? Analytic gammachirp (Irino and Patterson, 1997) Decomposition type (Irino and Unoki, 1999) Physiological gammachirp (Irino and Patterson, 2000) GTAsymmetric func. GTLP-ACHP-AC Level dependent shape Level independent shape Level dependent cf GTLP-ACHP-AC

7. Analytic gammachirp Gammachirp is a gammatone times an asymmetric function

8. Decompose asymmetric function a fixed lowpass AF and a variable highpass AF Passive BM

9. Physiological Gammachirp Fitted to human masking data of Rosen and Baker (1994), at 2 kHz Vary centre frequency of highpass, asymmetric function with level tails must converge tails converge Passive BM Gain change

10. Physiological gammachirp Fitted to revcor data of Carney et al. (1999)

11. Filterbank structure (A) Linear Gammatone Filterbank (D) Parameter Controller (c) Linear Gammachirp Filterbank Output (d) Gammachirp Filterbank Output (C) Asymmetric Compensation Filterbank (B) Linear Asymmetric Compensation Filterbank (b) Linear Gammatone Filterbank Output IIR gammatone （ Slaney, 1993 ） IIR Asymmetric Compensation Filter (Irino & Unoki, 1999) (a) Signal Input

12. Current work (1) Cross frequency parameter constraints in the gammachirp filterbank 500, 2k, 4k Fitted to human masking data of Rosen, Baker and Darling (1998) Left tails are a little high. It is possible to reduce the rms error. Note: 250, 1k, 3k, and 6kHz data omitted for clarity

13. Current work (2) Constructing a parameter controller (A) Linear Gammatone Filterbank (D) Parameter Controller (B), (C) Asymmetric Compensation Filterbank (C) Asymmetric Compensation Filterbank (A) Linear Gammatone Filterbank (D) Parameter Controller (B) Linear Asymmetric Compensation Filterbank Analytical type (Irino & Unoki, 1999) Physiological type LI Weighting Σ Convert Activity to Para- meter K-th Parameter Control Unit Varying Param. c Varying center freq. from adjacent channels k-th

14. Summary Physiological gammachirp filter »Consistent with physiological data –Level-independent chirp »Excellent fit to human masking data –Level-dependent gain and filter shape A physiological gammachirp filterbank »Enable us to simulate an active BM

15. Mathematical presentation Physiological Gammachirp Peak Frequency Passive gammachirpAsymmetric function Level-independent Level-dependent Center Frequency

16. IIR Asymmetric Compensation Filter 4 cascaded 2nd order IIR filter: Symmetrically placed poles and zeros, smaller than 1

17. Good Approximation ー Original Gammachirp -- IIR Gammachirp rms error: 0.68 dB (90 data pairs) ー Asymmetric function -- IIR Asymmetric Compensation filter

18. ポスターの構成 A3X15(1.6mX1.6m) Title (p.1) History (p.2-5) Physiological Gammachirp (p.6-10) Filterbank (p.11) Mathematical Presentation (p.15) (or p.15-17) Future work (p.12-14) ここをメインに