Acoustic Impedance Characteristics of Artificial Ears For Telephonometric Use. Gaëtan Lorho, Nokia Corporation

Transcription

1 ITU-T Workshop on "From Speech to Audio: bandwidth extension, binaural perception" Acoustic Impedance Characteristics of Artificial Ears For Telephonometric Use Gaëtan Lorho, Nokia Corporation Union

2 Overview Artificial ears for telephonometry Measurement campaign Acoustic impedance testing Impedance measurement results: Human ears Artificial ears Human vs. artificial ears Conclusions Paper available on the ITU-T workshop page ( Union 2

3 Artificial Ears for Telephonometry Analog of human ear for objective acoustic measurement Efficient and repeatable way of predicting acoustic performance of a handset in final usage case Standardization within industry: ITU-T Rec. P.57: Artificial Ears Ears should provide [ ] an overall acoustic impedance similar to that of the average human ear over a given frequency band Union 3

4 Artificial Ears for Telephonometry ITU-T Rec. P.57 Type 3.3 and 3.4 become industry de facto Primarily for use with a HATS ITU-T Rec. P.58 Head and torso simulator for telephonometry Type 3 - IEC occluded ear simulator with canal extension terminated in a: Type 3.3 pinna simulator (anatomically shaped) Type 3.4 pinna simulator (simplified) Union 4

5 Measurement Campaign ITU-T SG12 responsible for development of Rec. P.57 Recent effort to benchmark Type 3 ears against the average acoustic impedance of human ears Specific focus on: Mobile phone in hand-portable mode Measurement for a large number and range of human users Wide-band frequency range Round-robin campaign (multiple industry participants) Union 5

6 Acoustic Impedance Testing Mobile phone-like impedance probe provided by Brüel & Kjær Frequencydependent impedance measure close to the ECRP Union 6

7 Acoustic Impedance Testing Human measures: 5 contributing (independent) laboratories Subject gender and age demographic considered 106 subjects total measured 2 separate handset application force measures made per subject Normal application force (inferred from placement in silent condition) Firm application force (inferred from placement in lab. simulated noise field) Impedance measure at each ISO R40 1/12th oct. between 0.2-8kHz for each test case Union 7

8 Acoustic Impedance Testing Artificial ear measures: Commercially available artificial ears tested with same probe by each manufacturer Brüel & Kjær Type 3.3 ear HEAD acoustics Type 3.4 ear Measurement on HATS at standard position Application forces between 2 and 18N increasing by 2N steps Impedance measure at each ISO R40 1/12th oct. between 0.2-8kHz for each test case Union 8

9 Testing Results: Human Ears Statistical analysis for each individual 1/12th octave band All human measurements - "Firm" application force Human meas. - Firm ap. force - conf int. & stand dev Union 9

10 Testing Results: Human Ears Illustration of the two most important factors: Application force and Gender Average of human meas. - Normal versus Firm ap. force Average of human meas. per gender Blue: Normal application force Red: Firm application force Black: Male Blue: Female Union 10

11 Testing Results: Human Ears Detection of impedance response extrema Structural modeling of measures Impedance extrema of human meas. - Normal appl. force Three first maxima of human responses 3 individual Two first minima human responses of human responses 160 Structural description of human meas. - Normal appl. force Mean of extrema and ellipse covering 95% of the individual extrema Structural mean Union 11

12 Testing Results: Human Ears Comparative analysis of structural means Structural model of human meas. - Normal appl. force 95% confidence ellipse of the extremum mean Structural mean Structural model of hum. meas. - Norm. vs. firm appl. force Arithmetic mean and 95% conf. interv. Normal appl. force Blue: Normal application force Red: Firm application force Union 12

13 Testing Results: Artificial Ears Individual 1/12th oct. response for each artificial ear type per application force B&K - HATS meas. - type pressure levels HA - HATS meas. - type pressure levels From low (2N) to high pressure (18N) From low (2N) to high pressure (18N) Union 13

14 Human vs. artificial ears Human individual 1/12th octave band CI95% vs. artificial ears types Average of hum. meas. at Norm. and Firm force versus 3.3 Average of hum. meas. at Norm. and Firm force versus 3.4 From low (2N) to high pressure (18N) From low (2N) to high pressure (18N) Blue: Normal application force Red: Firm application force 160 Blue: Normal application force Red: Firm application force 160 Union 14

15 Human vs. artificial ears Human structural mean vs. artificial ears types Structural model of hum. meas. at Firm force versus 3.3 Mean of extrema and ellipse covering 95% of the individual extrema Structural mean Firm appl. force Structural model of hum. meas. at Firm force versus 3.4 Mean of extrema and ellipse covering 95% of the individual extrema Structural mean Firm appl. force From low (2N) to high pressure (18N) From low (2N) to high pressure (18N) Union 15

16 Conclusions The work highlighted the challenges of developing, using and interpreting artificial ears to predict the acoustic performance of mobile phones in the hand-held position Even more apparent when extending measurement beyond the typical narrowband frequencies The multiple statistical analysis methods described here give more perspectives on what the average human impedance response target is Discussion ongoing within ITU-T SG12 to make use of these results for current and future recommendations Union 16

17 Thank You Acknowledgements Nokia would like to thank the fellow contributors to the measurements presented herein, which included: Brüel & Kjær (Denmark) HEAD acoustics (Germany) Motorola (USA) Uniden (USA) Union 17