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Calibrations.md

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Acoustic calibrations for hearing research and audiological assessments

Basic topics

Calibration of stationary sounds (including pure tones)

  • Sound pressure is a local quantity (i.e., varies point-to-point in space, and instance-to-instance in time). What is intensity?
  • Considerations about coupling sound sources to the ear (free-field, circumaural, supra-aural, inserts), and simulating that situation (to match the average human adult or child) on a calibrating instrument (e.g., sound level meter)
  • Linearity and distortions of the sound source
  • Inter-channel interactions (e.g., left-right separation)
  • Calibration of the calibrating instruments using standard sources (e.g., pistonphone), and knowing the microphone frequency response on the calibrating instrument.

RETSPLs for different source-coupler combinations (i.e., headphones), and what dB HL means

  • Standard audiometric headphones + few other RETSPL reports in the literature
  • Brief aside on bone oscillators and RETFLs

Modifications/considerations for the calibration of transient sounds (e.g., clicks, short chirps, tones bursts) and non-stationary sounds (e.g., speech)

  • peSPL etc.
  • RMS for (longer) speech

Brief note about nonlinear and time-variant sources and acknowledge that they are beyond the scope of this document

  • Hearing aid compression
  • Automatic gain control

Advanced topics

Wideband immittance and individualized calibrations

  • What are standing waves and why we need to account for them (especially for inserts). Aside about warble tones in audiometry. Discussion of "uplift" and RECD.
  • Define immittance formally (impedance and admittance, resistance and conductance, absorbance and reflectance; Rosowski et al., 2013)
  • Directly measuring pressure using a probe microphone (aka "real-ear" calibrations)
  • Define FPL and contrast with incident pressure level
  • Considering pressure phase too vs. calibrations of intensity only
  • Performing FPL calibrations in situ as a substitute for real-ear measurements (Scheperle et al., 2011; Souza et al., 2014 and others) using two-port network theory (Thevenin/Norton).
  • Aside about checking for leaks of OAE/immittance probes (Groon et al., paper)
  • Define EPL, and note about measuring OAEs in EPL (Charaziak and Shera paper)
  • Note about wideband MEMR (Keefe et al., 2017; Bharadwaj et al., 2022)

Calibration of OAE microphones

  • Overall sensitivity and frequency response definitions
  • Using probe mic and surrogate "standard" mic in a cylindrical coupler (considerations for sound source high-frequency rolloff (e.g., trim tube)

Near vs. far-field effects (Mostly pointing to references and acknowledging that addressing them are beyond the scope of this document)

  • Wavefronts and divergence
  • Evanescent waves (mention Jon Siegel's homegrown beveled tip trick, and Kren's papers)

Relevant standards

  • Just a table, or perhaps skip altogether
  • IEC 60645-1:2015, ISO 8523-1:2010, ISO 389, Couplers: IEC 318, 711, 60318–1 60318-4 etc.

Useful references

Gøtsche-Rasmussen, K., Poulsen, T., & Elberling, C. (2012). Reference hearing threshold levels for chirp signals delivered by an ER-3A insert earphone. International journal of audiology, 51(11), 794-799.

Rasetshwane, D. M., & Neely, S. T. (2011). Calibration of otoacoustic emission probe microphones. The Journal of the Acoustical Society of America, 130(4), EL238-EL243.

Charaziak, K. K., & Shera, C. A. (2017). Compensating for ear-canal acoustics when measuring otoacoustic emissions. The Journal of the Acoustical Society of America, 141(1), 515-531.

Groon, K. A., Rasetshwane, D. M., Kopun, J. G., Gorga, M. P., & Neely, S. T. (2015). Air-leak effects on ear-canal acoustic absorbance. Ear and hearing, 36(1), 155.

Keefe, D. H., Feeney, M. P., Hunter, L. L., & Fitzpatrick, D. F. (2017). Aural acoustic stapedius-muscle reflex threshold procedures to test human infants and adults. Journal of the Association for Research in Otolaryngology, 18(1), 65-88.

Liu, Y. W., Sanford, C. A., Ellison, J. C., Fitzpatrick, D. F., Gorga, M. P., & Keefe, D. H. (2008). Wideband absorbance tympanometry using pressure sweeps: System development and results on adults with normal hearing. The Journal of the Acoustical Society of America, 124(6), 3708-3719.

Rosowski, J. J., Stenfelt, S., & Lilly, D. (2013). An overview of wideband immittance measurements techniques and terminology: you say absorbance, I say reflectance. Ear and hearing, 34 Suppl 1(0 1), 9S–16S. https://doi.org/10.1097/AUD.0b013e31829d5a14

Scheperle, R. A., Goodman, S. S., & Neely, S. T. (2011). Further assessment of forward pressure level for in situ calibration. The Journal of the Acoustical Society of America, 130(6), 3882-3892.

Souza, N. N., Dhar, S., Neely, S. T., & Siegel, J. H. (2014). Comparison of nine methods to estimate ear-canal stimulus levels. The Journal of the Acoustical Society of America, 136(4), 1768-1787.

Bharadwaj HM, Hustedt-Mai AR, Ginsberg HM, Dougherty KM, Muthaiah VPK, Hagedorn A, Simpson JM, Heinz MG. Cross-Species Experiments Reveal Widespread Cochlear Neural Damage in Normal Hearing. [In Press] Communications Biology. bioRxiv: https://doi.org/10.1101/2021.03.17.435900.

Valente, M., Potts, L. G., Valente, L. M., Vass, W., & Goebel, J. (1994). Intersubject variability of real-ear sound pressure level: Conventional and insert earphones. Journal of the American Academy of Audiology, 5(6).

Munro, K. J., & Davis, J. (2003). Deriving the real-ear SPL of audiometric data using the “coupler to dial difference” and the “real ear to coupler difference”. Ear and Hearing, 24(2), 100-110.

Vencovsky, V., Rund, F., & Slegl, D. (2018). Reference equivalent threshold sound pressure levels for nonaudiometric headphones. Journal of the Audio Engineering Society, 66(3), 167-171.