You like old parts, don't you?
The old DS1669 digital pot is linear. A volume control is supposed to be logarithmic.
Maxim-IC have some logarithmic digital volume controls.
What will the speech filter do? Remove the very important high audio frequencies of consonants and remove realistic low frequencies?
We can hear from 20Hz to 20kHz. Our hearing doen't make everything sound like a 300Hz to 3kHz telephone.
Modern hearing aids are programmable to fit the frequency response of the wearers ear. Could be a tiny DSP.
Wonder why the OP is building one? You'll never be able to make one as small as a professional aid. Why a digital volume control?
What will the speech filter do? Remove the very important high audio frequencies of consonants and remove realistic low frequencies?
We can hear from 20Hz to 20kHz. Our hearing doen't make everything sound like a 300Hz to 3kHz telephone.
The purpose of my speech filter(idea) is to eliminate noise from signal containing speech and noise.I assume that the user doesnt want to hear background noise,and he/she activate the filter.It just a random idea sir.Correct me if im wrong.
Modern hearing aids are programmable to fit the frequency response of the wearers ear. Could be a tiny DSP.
Wonder why the OP is building one? You'll never be able to make one as small as a professional aid. Why a digital volume control?
Im intend to designing a low cost,effective and high performance hearing aid system.Programmable hearing aid is very expensive which cost the patient around $900-$3000,depending on it technology and brand.
This is a project which i need to study the cases of hearing impaired and hardware design is a part of my project.
The design and analysis part is the most challenging part for me.
The purpose of the digital volume is to replace mechanical volume control.Actually I had design a hearing aid system early in my project(I design the hearing aid just using LM 386 and uni directional ECM but it just a demo kit which allow me to understand more the concept.
Im also looking for software to do analysis for my design in near future.Does MATLAB or Pspice are suitable for this?
The frequency equalization require me to implement dsp chip,i guess.Im designing a high performance analog circuit.However, i found a journal which they design a hybrid analog digital hearing aid.They using a micro controller to control the analog circuit.Unfortunately,im just understand the concept but failed to catch the design.
You can make an analog equalizer. One parametric adjustable frequency with adjustable Q for its bandwidth and adjustable boost should work pretty well.
A simple treble frequencies boost circuit will also work pretty well.
A second-order Sallen and Key lowpass filter with its Q set too high boosts the high audio frequencies peaking at a frequency close to its cutoff frequency.
You can use any opamp that is low noise and has the power supply voltage range that you want.
A second order Sallen and Key filter can have equal component values and has a flat response then sharp cutoff (Butterworth) when its gain is 1.6 times. When its gain is greater than 3 then it oscillates. When its gain is between 1.6 and 3 then it has a peak near its cutoff frequency. The peak is equalization. The cutoff reduces noise (and important high audio frequencies which are the consonants of speech).
Why are you building this? Is it a school project?
Even with modern small ICs and other components it will be about the size of a cell phone (if your skilled)
Why are you building this? Is it a school project?
Even with modern small ICs and other components it will be about the size of a cell phone (if your skilled)