Patent Application
20210029451
In hearing aids, such as the contact hearing aids available from Earlens Corporation, sliding bias algorithms may be used to lower the power consumption by, for example, manipulating the DC offset of the audio signal before it is input to a modulator. In these devices, an algorithm is used to vary a bias, including a negative bias, according to the output sound level. By varying the bias amount it is possible to manage the power consumption by the output device, e.g. a laser. A similar design may be used in a class A amplifier, where the bias voltage is lowered when the signal is small, thereby reducing the wasted power. This is particularly beneficial in systems, such as light-driven contact hearing aids, where, as in a class A amplifier, the bias current flows even when there is no output audio signal.
However, the use of sliding bias algorithms may generate artifacts which are audible to the user, such as, for example, saturation artifacts. In prior systems, saturation artifacts may have been reduced or eliminated by using a first output limiter to attenuate signals that would exceed the momentary signal intensity limit, along with a second limiter that similarly attenuates signals that would exceed the digital saturation level.
In devices using the present invention, audible artifacts may be reduced or eliminated by designing the system such that the sliding bias level is fed back to an output limiter so that a single algorithm manages all saturation artifacts. In embodiments of the invention, this feedback loop will eliminate the need for a second output limiter.
The foregoing and other objects, features and advantages of embodiments of the present inventive concepts will be apparent from the more particular description of preferred embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same or like elements. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the preferred embodiments.
In devices utilizing the present invention, such as contact hearing systems, when the signal level changes, specifically, when it increases, the (e.g., negative) bias level needs to increase (e.g., towards 0) in order to handle the larger input signal without saturation. If the bias level does not rise fast enough, the output signal will be distorted. Distortion may include distortion caused by saturation, where the output is clipped. In the present invention, the problem of bias levels that do not rise fast enough is addressed by a system that employs an output limiter that applies brief attenuation to prevent sudden saturation. In embodiments of the invention, the limiting level is controlled by the current bias level. In embodiments of the invention, the output limiter, rather than managing only digital saturation, and therefore employing a fixed limit threshold, precedes the sliding bias in the signal processing pipeline. In embodiments of the invention, the output limiter threshold will vary with the sliding bias. Designs such as those described will mitigate digital saturation. Designs such as those described with also mitigate underflow due to sudden signal onsets and low sliding bias levels.
In embodiments of the invention, the output of sliding bias circuit 502 may be delayed by, for example, delay circuit 506 to provide AGCO circuit 504 with time to react to the feedback from bias circuit without increasing the latency of the system. In embodiments of the invention, the output of sliding bias circuit 502 may be delayed, by, for example, delay circuit 506 to provide AGCO circuit 504 with time to react to the feedback from sliding bias circuit 502 without increasing the latency of the audio path through the system. In embodiments of the invention, the output of bias circuit 502 may be delayed to reduce latency of the system, improving sound quality. In embodiments of the invention, the output of sliding bias circuit 502 may be delayed to provide AGCO circuit 504 with time to react to the feedback from the bias circuit. In embodiments of the invention, the output of bias circuit 506 is always non-positive.
In embodiments of the invention, the input X to sliding bias control circuit 500 may be an audio signal. In embodiments of the invention, the input X to sliding bias control circuit 500 may be an audio signal which is an output of external microphone 310. In embodiments of the invention, the input X to sliding bias control circuit 500 may be an audio signal which is an output of analog to digital converter 320. In embodiments of the invention, external microphone 310 may be connected to an A-to-D converter 320 with the input X as the output of A-to-D converter 320. In embodiments of the invention, the input X to sliding bias control circuit 500 may be an audio signal which is an output of signal processor 330, which may be a digital signal processor. In embodiments of the invention, sliding bias control circuit 504 may include an automatic gain control circuit 504 which may limit the gain applied to the input X. In embodiments of the invention, automatic gain control circuit 504 may attenuate input X if it is too large. In embodiments of the invention, automatic gain control circuit 504 may attenuate input X if it is too large (e.g., in the event that X is an audio signal representing a loud sound).
In embodiments of the invention, sliding bias control circuit 500 may include a sliding bias circuit 502. In embodiments of the invention, automatic gain control circuit 504 may receive an input signal from sliding bias circuit 502 which may be used to, for example, define a threshold beyond which automatic gain control circuit 504 limits the gain applied to input X. In embodiments of the invention, sliding bias circuit 502 may be used to control the level of bias added to the output Y of automatic gain control circuit 504. In embodiments of the invention, sliding bias circuit 504 may shift the bias such that a smaller (e.g., lower or more negative) bias is added to output Y when the input X is a small signal. In embodiments of the invention, sliding bias circuit 504 may shift the bias such that a larger bias is added to output Y when the input X signal is large, to, for example, prevent output Y from being clipped.
In embodiments of the invention, sliding bias control circuit 500 may include delay circuit 506, which may be used to delay the output of sliding bias circuit 502 such that the output of sliding bias circuit 502 reaches summing circuit 510 before the output Y of automatic gain control circuit 504. In embodiments of the invention, the delay introduced by delay circuit 506 is intended to make sure that the AGCO 504 has applied the desired level change before the bias is applied by SB 502. Note that the delay 506 is applied to the control signal and therefore it does not affect the overall latency of the sound signal. In embodiments of the invention, there may be a delay in resetting the threshold value in automatic gain control circuit 504, and the delay introduced by delay circuit 506 may compensate for that delay.
In embodiments of the invention, sliding bias control circuit 500 may include smoothing circuit 508. In embodiments of the invention, smoothing circuit 508 may be used to, for example, integrate the output of sliding bias circuit 502 to smooth out changes in the output of sliding bias circuit 502. In embodiments of the invention, smoothing circuit 508 may be used to ramp the output of sliding bias circuit 502 from one value to another, thus preventing abrupt changes in the value of the output of sliding bias circuit 502 which might be audible to a user.
In embodiments of the invention, sliding bias control circuit 500 may include summing circuit 501. In embodiments of the invention, summing circuit 501 may be used to sum the output of automatic gain control circuit 504 to the output of sliding bias circuit 502 in order to add a bias (which may be a negative bias) to output Y of automatic gain control circuit 504 and generate output Z of sliding bias control circuit 500. In embodiments of the invention, summing circuit 501 may be used to sum the output of automatic gain control circuit 504 to the delayed and smoothed output of sliding bias circuit 502 in order to add a bias (which may be a negative bias) to output Y of automatic gain control circuit 504 and generate output Z of sliding bias control circuit 500.
In embodiments of the invention, the invention may be described by the following equations.
AGCO Gain g(t):
g(Tn-1≤t<Tn)=f(t:g(Tn-1),Gn-1,Gn) s.t. g(Tn)≤Gn(see below)
y
n
=g(Tn-1≤t<Tn)*xn-1
Bias:
z
n
=y
n
+b
n
B
n*=min(Bn,Bn-1)
About f(t: g(Tn-1), Gn-1, Gn):
G
Tgt,n=min(Gn_1,Gn)
if GTgt,n<g(Tn-1)):
else:
Embodiments of the present invention may be directed to a method of controlling a hearing aid circuit including a sliding bias circuit, wherein the method includes the steps of: receiving an audio input signal; adjusting the gain of the input signal; transmitting the gain adjusted input signal to a sliding bias calculator and a summing circuit; wherein the level of gain applied to the input signal is a function of the output of the sliding bias circuit. In methods according to the present invention, the method further includes the step of delaying the output of the sliding bias circuit. In methods according to the present invention, the method further includes the step of adding the delayed output of the sliding bias circuit to the output of the automatic gain control circuit to create an output which is gain controlled and includes a bias component.
Embodiments of the present invention include a contact hearing system including a sliding bias circuit, wherein the sliding bias circuit includes an input; an automatic gain control circuit connected to the input; a sliding bias calculator connected to the output of the automatic gain control circuit; an output of the sliding bias calculator connected to a control input of the automatic gain control circuit such that the output of the automatic gain control circuit is a function of the output of the sliding bias calculator. Embodiments of the present invention may further include a delay circuit connected to the output of the sliding bias calculator. Embodiments of the present invention may further include a summing circuit connected to an output of the delay circuit and the output of the automatic gain control circuit, wherein the output of the summing circuit is a gain modulated audio signal including a bias component.
Audio Processor—A system for receiving and processing audio signals. Audio processors may include one or more microphones adapted to receive audio which reaches the user's ear. The audio processor may include one or more components for processing the received sound. The audio processor may include digital signal processing electronics and software which are adapted to process the received sound. Processing of the received sound may include amplification of the received sound. The output of the audio processor may be a signal suitable for driving a laser located in an ear tip. The output of the audio processor may be a signal suitable for driving an antenna located in an ear tip. The output of the audio processor may be a signal suitable for driving an inductive coil located in an ear tip. Audio processors may also be referred to as behind the ear units or BTEs.
Contact Hearing System—A system including a contact hearing device, an ear tip and an audio processor. Contact hearing systems may also include an external communication device. An example of such system is an Earlens hearing-aid that transmits audio signal by laser to a contact hearing device which is located on or adjacent to the ear drum. The contact hearing system may also be referred to as a smart lens.
Contact Hearing Device—A tiny actuator connected to a customized ring-shaped support platform that floats on the ear canal around the eardrum, where the actuator directly vibrates the eardrum causing energy to be transmitted through the middle and inner ears to stimulate the brain and produce the perception of sound. The contact hearing device may comprise a photodetector, a microactuator connected to the photodetector, and a support structure supporting the photodetector and microactuator. The contact hearing device may comprise an antenna, a microactuator connected to the antenna, and a support structure supporting the antenna and microactuator. The contact hearing device may comprise a coil, a microactuator connected to the coil, and a support structure supporting the coil and microactuator. The contact hearing device may also be referred to as a Tympanic Contact Actuator (TCA), a Tympanic Lens, a Tympanic Membrane Transducer (TMT), or a smart lens.
Ear Tip—A structure designed to be placed into and reside in the ear canal of a user, where the structure is adapted to receive signals from an audio processor and transmit signals to the user's tympanic membrane or to a device positioned on or near the user's tympanic membrane (such as, for example, a contact hearing device). In one embodiment of the invention, the signals may be transmitted by light, using, for example, a laser positioned in the light tip. In one embodiment of the invention, the signals may be transmitted using radio frequency, using, for example, an antenna connected to the Ear Tip. In one embodiment of the invention, the signal may be transmitted using inductive coupling, using, for example, a coil connected to the ear tip. The ear tip may also be referred to as a light tip, magnetic tip, or mag tip.
Light-Driven Hearing Aid System—A contact hearing system wherein signals are transmitted from an ear tip to a contact hearing device using light. In a light driven hearing system, light (e.g. laser light) may be used to transmit information, power, or both information and power to a contact hearing device.
RF-Driven Hearing Aid System—A contact hearing system wherein signals are transmitted from an ear tip to a contact hearing device using radio frequency electromagnetic radiation. In an RF driven hearing system, electromagnetic radiation may be used to transmit information, power, or both information and power from the ear tip to the contact hearing device.
Inductively-Driven Hearing Aid System—A contact hearing system wherein signals are transmitted from an ear tip to a contact hearing device using inductive coupling. In an inductively driven hearing system, magnetic waves may be used to transmit information, power, or both information and power from the ear tip to the contact hearing device.
Light Tip—An ear tip adapted for use in a light driven hearing aid system. A light tip may include a laser.
Mag Tip—An ear tip adapted for use in an inductively driven hearing aid system. The mag tip may include an inductive transmit coil.
While the preferred embodiments of the devices and methods have been described in reference to the environment in which they were developed, they are merely illustrative of the principles of the present inventive concepts. Modification or combinations of the above-described assemblies, other embodiments, configurations, and methods for carrying out the invention, and variations of aspects of the invention that are obvious to those of skill in the art are intended to be within the scope of the claims. In addition, where this application has listed the steps of a method or procedure in a specific order, it may be possible, or even expedient in certain circumstances, to change the order in which some steps are performed, and it is intended that the particular steps of the method or procedure claim set forth herebelow not be construed as being order-specific unless such order specificity is expressly stated in the claim.
This application is a continuation of PCT Application No. PCT/US19/26361, filed Apr. 8, 2019; which claims the benefit of U.S. Provisional Application No. 62/654,822, filed Apr. 9, 2018; the entire contents of which are herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62654822 | Apr 2018 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2019/026361 | Apr 2019 | US |
| Child | 17066345 | US |
