Communication acoustics Ch 9: Basic function of hearing

Transcription

1 Communication acoustics Ch 9: Basic function of hearing Ville Pulkki and Matti Karjalainen Department of Signal Processing and Acoustics Aalto University, Finland February 20, 2015

2 This chapter Effective hearing area Spectral masking Temporal masking Frequency selectivity of hearing

3 Effective hearing area Dynamic range of hearing Sound pressure μpa Jet engine (25 m) Rock band Heavy truck Normal discussion Library Quiet sleeping room SPL db Jet plane takeoff (100 m) Jackhammer Street noise Busy office Living room Quiet forest Hearing threshold

4 Effective hearing area Equal loudness contours Sound pressure level [db] Hearing threshold (MAF) Loudness level [phon] k 2k 4k 8k 16k Frequency [Hz]

5 Sound level and frequency weighting curves Weighting filters for sound level measurement (A most common) Measured pressure level should match the loudness perceived by the listener 20 Relative sound pressure level [db] D C A C,B D B A k 2k 5k 10k 20k Frequency [Hz]

6 Masking effect A loud sound makes a weaker sound imperceptible Categories and aspects of masking Frequency masking Temporal masking Time-frequency masking Frequency selectivity of the auditory system Psychophysical tuning curves Critical band Bark bandwidth ERB bandwidth

7 Frequency masking Masking by white noise Test tone SPL [db] Frequency [khz] L WN = 50 db db 30 db 20 db 10 db 20 0 db 10 db ERB scale Adapted from Fastl and Zwicker (2007)

8 Frequency masking Masking by narrow-band noise Test tone SPL [db] Frequency [khz] f c = 250 Hz 50 f c = 1 khz f c = 4 khz ERB scale Adapted from Fastl and Zwicker (2007)

9 Frequency masking Masking as function of the level of masker Frequency [khz] L = 100 db CB Test tone SPL [db] db db db 20 db ERB scale Adapted from Fastl and Zwicker (2007)

10 Frequency masking Frequency masking by lowpass and highpass noise Frequency [khz] Test tone SPL [db] 20 L WN = db L WN = 20 db L WN = 0 db ERB scale Adapted from Fastl and Zwicker (2007)

11 Frequency masking Frequency masking by 1kHz tone Frequency [khz] mixture of tones beating mixture of tones beating mixture of tones beating Magnitude of secondary tone [db] primary, secondary & difference tone primary & secondary tone primary tone primary, secondary primary, secondary & difference tone & difference tone primary & diffe rence tone primary tone only ERB scale Adapted from Wegel and Lane (1924)

12 Frequency masking Frequency masking by harmonic tone complex Test tone SPL [db] Frequency [khz] db 50 db ERB scale Adapted from Fastl and Zwicker (2007)

13 Temporal masking Masking before and after a noise signal Forward masking (noise masks sounds forward in time) / backward masking 80 test tone level [db] backward masking forward masking (postmasking) threshold of test tone without masking time [ms]

14 Temporal masking Peak level of test tone [db] Forward masking with different masking levels L WN = 80 db Delay t d [ms] 0,5s t d t Adapted from Fastl and Zwicker (2007)

15 Temporal masking Level of test tone [db] Forward masking with different lengths of masking noise ms 5 5 ms 200 ms f T = 2 khz Delay t d [ms] t d 5 t Adapted from Fastl and Zwicker (2007)

16 Temporal masking Masking by an impulse relative level of probe impulse [db] hearing threshold of probe impulse a single masker impulse position of probe impulse [ms] Adapted from Feth and O Malley (1977)

17 Frequency selectivity of hearing When sinusoids are far from each other in frequency, they are perceived as two static sinusoids When the frequencies are enough near, sinusoids interact Frequency masking has strongest effect to nearby frequencies Humans have a certain frequency selectivity All frequency components inside "critical band" are merged together, not accessible separately

18 Frequency selectivity of hearing Psychophysical tuning curves Masking threshold - low-level sinusoid as signal and narrowband noise as masker 80 Frequency [khz] Test tone SPL [db] ERB scale Adapted from Vogten (1974)

19 Measuring the width of critical bands Experiment: loudness vs. bandwidth of noise power spectral density Δf = 200Hz 1Hz 100Hz frequency [khz]

20 Measuring the width of critical bands Loudness increases when the banwidth increases the critical bandwidth 80 loudness level [phon] 75 Mid frequency = 1 khz Sound pressure level L p = db (constant) bandwidth [Hz]

21 Measuring the width of critical bands Masking threshold of the signal is measured as function of the width of passband Equivalent rectangular bandwidth scale (ERB scale) Δf Δf magnitude [db] noise band auditory filter signal noise band linear frequency scale

22 Width of critical bands Bark and ERB dependence on frequency 12 Auditory bandwidth f [Hz] f ERB f Bark Q = f c / f /6 1/3 1/2 Bandwidth in octaves Frequency [Hz] Frequency [Hz]

23 Auditory frequency scales Stack ERB and Bark bandwidths starting from a low frequency 35 Auditory scale ERB scale z ERB Bark scale z Bark Frequency [Hz]

24 References These slides follow corresponding chapter in: Pulkki, V. and Karjalainen, M. Communication Acoustics: An Introduction to Speech, Audio and Psychoacoustics. John Wiley & Sons, 2015, where also a more complete list of references can be found. References used in figures: Fastl, H. and Zwicker, E. (2007) Psychoacoustics Facts and Models. Springer. Feth, L.L. and O Malley, H. (1977) Influence of temporal masking on click-pair discriminability. Percep. Psychophys., 22(5), Vogten, L. (1974) Pure-tone masking: A new result from a new method Facts and Models In Hearing, Springer. pp Wegel, R. and Lane, C. (1924) The auditory masking of one pure tone by another and its probable relation to the dynamics of the inner ear. Phys. Rev. 23(2), Basic function of hearing 24/24 Pulkki February 20, 2015 Dept Signal Processing and Acoustics