Physiological basis of sound design. Prof. Dr. med. Eckhard Hoffmann Dipl.-Ing. (FH) Steffen Kreikemeier Aalen University of Applied Sciences

Transcription

1 Physiological basis of sound design Prof. Dr. med. Eckhard Hoffmann Dipl.-Ing. (FH) Steffen Kreikemeier Aalen University of Applied Sciences

2 Index of contents Physiological basis of the inner ear Organ of Corti Inner and outer hair cells Otoacoustic emissions (OAE) Types of OAE Results of diploma thesis Influence of visual stimuli on OAE Effects of presbyacusis on sound design

3 Inner ear Physiological basis of the inner ear Outer ear Concha Ear canal Middle ear Eardrum Hammer (Malleus) Anvil (Incus) Stirrup (Stapes) Inner ear Cochlea Equilibrium organ Hammer Equilibrium organ Cochlea Tuba auditiva Eardrum Ear canal Outer, middle and inner ear Source: E. Hoffmann

4 Inner ear Physiological basis of the inner ear Antrum mastoideum Canalis musculotubarius Eardrum Cellulae mastoideae Hypotympanon Silicone cast of the middle ear Source: E. Hoffmann Ossicles compared to a one cent coin Source: E. Hoffmann

5 Inner ear how it works Physiological basis of the inner ear Sound waves reach the eardrum through the ear canal Middle ear works as a impedance converter Traveling wave emerges on basilar membrane of the cochlea Bark scale serves as psychoacoustic scale for tone pitch

6 Organ of Corti Physiological basis of the inner ear Illustration of the organ of Corti Source: E. Hoffmann

7 Organ of Corti Physiological basis of the inner ear Amplification is realized by the organ of Corti, which consists of the basilar membrane, tectorial membrane as well as outer and inner hair cells Active movement of outer hair cells are responsible for a precise frequency adjustment Unlike high levels of sound, low levels are amplyfied up to 60 db SPL High levels of sound lead to a temporary threshold shift (TTS) Active movement of outer hair cells Source: E. Hoffmann

8 Inner ear how it works Physiological basis of the inner ear Traveling waves on basilar membrane Source: E. Hoffmann

9 Hair Cells Physiological basis of the inner ear Approximately hear cells located on the basilar membrane One row of approx inner hear cells are responsible for sensory perception Three rows of overall approx outer hear cells (OHC s) amplify nonlinear and differentiate a sharp traveling wave

10 Hair Cells Physiological basis of the inner ear Scanning Electron Microscopy picture of a one year old rat scale bar: 15 µm Source:

11 Outer Hair Cell Physiological basis of the inner ear Rock Around The Clock Hair Cell Video By Jonathan Ashmore

12 Outer Hair Cell Physiological basis of the inner ear Only OHC s are able to change their length at acoustic frequencies Prestin works as a motor protein It is the only protein of the Gene Family of anion transporter-related proteins that has the ability for electromotility Anions like chlorite move within the cell in case of deor hyperpolarization

13 Types of OAE Otoacoustic Emission OAE Due to the movement, outer hair cells emit sounds These sounds are called otoacoustic emissions (OAE) and can be measured in the ear canal OAE differ in the way they were measured Clinical most important: with acoustic stimulus Because of the non linearity of the ear, the signals f1 and f2 lead distortion products with a frequency of 2f1 -f2

14 Types of OAE Otoacoustic Emission OAE Types of otoacoustic omissions Spontaneous otoacoustic emissions (SOAEs) Transient otoacoustic emissions (TOAEs) Evoked otoacoustic emissions (EOAEs) Sustainedfrequency otoacoustic emissions (SFOAEs) Distortion product otoacoustic emissions (DPOAEs)

15 Influence of visual stimuli on OAE Otoacoustic Emission OAE Influence of visual stimuli is known and important for: Sound Design Hearing Aid Fitting Psychoacoustic Music industry And many more

16 Influence of visual stimuli on OAE Otoacoustic Emission OAE Source: aboutpixel.de / wald des todes Christoph Ruhland

17 Influence of visual stimuli on OAE Otoacoustic Emission OAE Purpose of the diploma thesis: Verify influence of visual stimuli on the acoustic system on the basis of objective procedures. Are effects represented in the inner ear by OAE? Does a different stimulus (video, text etc.) lead to a different result?

18 Influence of visual stimuli on OAE Otoacoustic Emission OAE Methods and procedures 55 Subjects between 21 and 70 years Average threshold between 500 Hz and 6 khz 20 db HL (Hearing Level) DPOAE measurements with and without visual stimuli Tympanogram

19 Influence of visual stimuli on OAE Otoacoustic Emission OAE Screenshot OAE measurements

20 Influence of visual stimuli on OAE Otoacoustic Emission OAE Screenshots testmaterials

21 Influence of visual stimuli on OAE Otoacoustic Emission OAE Example: Gradient with / without visual stimulus 10 5 db (SPL) 0-5 Without visual stimulus With visual stimulus , db (SPL) db (SPL) 0,5 0, ,5 5 rot blau grün türkscih deutsch wiese bw_1_1 bw_1_2 tests säge coyotee optiker damen dunkel normal_ normal_ 3 2 Gradient of calculated level differences of 15 tests

22 Influence of visual stimuli on OAE Otoacoustic Emission OAE Hypothesis: Visual stimuli effect the sensibility of the inner ear Leaded to: Measure the effects on the inner ear via otoacoustic emissions No difference between tests were established Effects are existent, but not realized in the inner ear

23 Effects of presbyacusis on sound design Otoacoustic Emission OAE Most people over 60 years have some hearing loss Primary loss of high frequencies Hearing loss [db HL] Frequency [khz] 0,125 0,25 0,5 1 1, Age Hearing loss in reference to age according ISO 7029 Source: E. Hoffmann

24 Effects of presbyacusis on sound design Otoacoustic Emission OAE People with hearing loss have a different perception of sounds Presbyacusis makes it hard to understand speech in noise Big communities Films with background music Processing of signals has changed and is perhaps slower

25 Effects of presbyacusis on sound design Otoacoustic Emission OAE Helpful for people with presbyacusis would be: Speech louder than music or noise Speech from in front of listener (Surround-Sound) Not helpful would be: Present everything louder incl. music or noise Consequences Sound improvement for older people Include people with hearing loss in sound design Different versions for different consumers (compare homepages for visually impaired people)

26 Physiological basis of sound design Thank you for listening! Any questions?

27 Physiological basis of sound design Prof. Dr. Eckhard Hoffmann Aalen University of Applied Sciences Department of Optometrie and Audiology Phone: +49 (0) Dipl.-Ing. (FH) Steffen Kreikemeier Universitätsklinikum Gießen und Marburg GmbH Department of Audiology Phone: +49 (0)