Method of processing a signal in a hearing instrument, and hearing instrument
A method of estimating an acoustic transfer quantity representative of a sound pressure transfer to the eardrum includes the steps of measuring, by an ear canal microphone of the hearing instrument, an acoustic signal in the ear canal when a sound signal is emitted into the ear canal by a receiver of the hearing instrument, the ear canal microphone being in acoustic communication with the ear canal, determining, from the acoustic signal and from a frequency dependent reference characteristics of the hearing instrument, an ear canal impedance, and, calculating, from the ear canal impedance, an estimate of the acoustic transfer quantity.
1. A method of estimating an acoustic transfer quantity representative of a sound pressure transfer to the eardrum of an ear, when a hearing instrument is coupled to the ear, the method comprising the steps of
measuring, by an ear canal microphone of the hearing instrument, an acoustic signal in the ear canal when a sound signal is emitted into the ear canal by a receiver of the hearing instrument, the ear canal microphone being in acoustic communication with the ear canal;
determining, from the acoustic signal and from a frequency dependent ear independent reference characteristics of the hearing instrument, an ear canal impedance; and
calculating, from the ear canal impedance, an estimate of the acoustic transfer quantity.
2. The method according to claim 1 , wherein the ear independent reference characteristics are reference characteristics of an acoustic quantity of the hearing instrument coupled to a standard acoustic coupler.
3. The method according to claim 1 , further comprising, prior to the step of determining the ear canal impedance, the steps of
coupling the hearing instrument to a standard acoustic coupler,
emitting, by the receiver of the hearing instrument, a sound signal into the standard acoustic coupler,
measuring a standard coupler acoustic signal by the ear canal microphone coupled to the standard coupler, and
obtaining the reference characteristics from the standard coupler acoustic signal.
4. The method according to claim 3 , wherein the standard acoustic coupler is chosen to have a custom manufactured interface with a shape adapted to the shape of a custom manufactured shell of the hearing instrument.
5. The method according to claim 1 , comprising, prior to calculating an estimate of the acoustic transfer quantity, at least one of the steps of:
a. estimating a physical property of the ear canal; and
b. estimating a leak impedance of sound leaking through a hearing instrument vent and/or through a leaky shell,
wherein, in the step of calculating the estimate, the result of estimating the physical property and/or the leak impedance, respectively, is used as a further input quantity in addition to the ear canal impedance.
6. The method according to claim 5 , wherein the physical property of the ear canal is chosen to comprise a geometrical quantity characteristic of the ear canal.
7. The method according to claim 6 , wherein the physical property is chosen to comprise a distance between a sound emission plane and the eardrum.
8. The method according to claim 7 , wherein the step of estimating the distance comprises performing a frequency analysis of the acoustic signal, identifying a frequency at which the signal is at a local extreme and calculating the distance to correspond to a quarter wavelength corresponding to the identified frequency.
9. The method according to claim 1 , wherein the transfer quantity is a Real-Ear-to-Coupler difference (RECD) or a Real Ear Occluded Gain (REOG).
10. The method according to claim 1 further comprising the step of adjusting a hearing instrument signal processing parameter dependent on the results of the estimate of the transfer quantity.
11. The method according to claim 1 , wherein in the calculation of the ear canal impedance, no measurement data obtained by any separate probe introduced in the ear are used.
12. A hearing instrument comprising at least one input microphone, at least one signal processor, at least one receiver, and at least one ear canal microphone, the receiver and the ear canal microphone being arranged to be in direct communication with a volume defined between an earpiece of the hearing instrument and the eardrum, the signal processor being configured to carry out the method according to claim 1 .
13. The hearing instrument according to claim 12 , wherein a receiver sound opening at which the signal emitted by the receiver exits into the volume and an ear canal microphone sound opening at which the ear canal microphone or a tubing connected to it connects to the remaining volume define a plane that is approximately perpendicular to an ear canal axis.