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Nick Gray

 

Nicholas Gray

Nicholas has worked in the Semiconductor industry for over 30 years and has authored a number of published articles about data converters (ADCs and DACs) and signal integrity issues.

 

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  • Nick:  I'm an ancient engineer with a modern-day need for an improved hearing aid.  What I need and what I want to develop is a simpler yet more effective digital hearing aid. All hearing aids leave one  with the  ' I hear but I don't understand'  feeling which is common-place to most hard of hearing (HOH) individuals..  In order to improve on these hearing aids, I want to copy the  design of a digital audio amplifier and add on one more stage.  That stage would take the output voltages from the A to D converter and modify it to a new set of voltages which are more compatible with the HOH  ear.  It has been suggested that I create a look-up table to change the output from say a typical  eight-bit converter (256 bits) to levels of my own choosing.   How do I go about creating a look-up table to do this?

  • in reply to Former Member
    Ken Boyce has given an excellent response. However, I would not use an associative or content addressable memory because they are more expensive than necessary for your application. I believe that an EEPROM is the best solution. For the sake of small size, I would use a serial output ADC and an EEPROM with a serial interface. The output from the ADC is the address of the EEPROM and the data at that address would be the new data to be used. This essentially converts each ADC output word to a new word. Your task is to determine what the relationship between the ADC output and the desired word.

    I am not really into audio, but from what little I know of hearing problems it seems to me that most people suffering from loss have that loss at certain frequencies or range of frequencies. This being the case, I would think that the best solution would be to amplify some frequencies more than others. This would have to be different for each individual, so a tunable filter would be needed that would be adjusted by the doctor or Audiologist for a given individual. My understanding is that such devices are already available, but I am not positive of this.
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  • in reply to Former Member
    Ken Boyce has given an excellent response. However, I would not use an associative or content addressable memory because they are more expensive than necessary for your application. I believe that an EEPROM is the best solution. For the sake of small size, I would use a serial output ADC and an EEPROM with a serial interface. The output from the ADC is the address of the EEPROM and the data at that address would be the new data to be used. This essentially converts each ADC output word to a new word. Your task is to determine what the relationship between the ADC output and the desired word.

    I am not really into audio, but from what little I know of hearing problems it seems to me that most people suffering from loss have that loss at certain frequencies or range of frequencies. This being the case, I would think that the best solution would be to amplify some frequencies more than others. This would have to be different for each individual, so a tunable filter would be needed that would be adjusted by the doctor or Audiologist for a given individual. My understanding is that such devices are already available, but I am not positive of this.
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  • in reply to nickgray
    Hi Nick:  I want to thank you and Ken Boyce for sharing your expertise with me.  I am what might be called an ancient engineer.  It seems that in my educational background I have always been two steps behind the latest technology.   Would you specify the name of an A to D converter and associated serial EPROM that you have suggested that I use.  I will then try to learn enough programming to program according to my own idea for a better hearing aid.  I am looking at the problem from the standpoint of modulation, not frequency. Any other advise would be much appreciated.   Nate Almond
  • in reply to Former Member

    Hi Nate,

     

    One ADC you could look at is the AD9057   ( http://www.analog.com/static/imported-files/data_sheets/AD9057.pdf  ).   Figure 7 shows the evaluation board schematic.  The ENCODE signal would be the clock rate at which you want to convert the analog data.   For voice data, 8KHz sample rate is routinely used, but maybe you want higher resolution, and you could use 16KHz.  The 74ACQ574SJ74ACQ574SJ acts as a temporary data latch between encode cycles.  The output data is 8 bit parallel which could be used as the address to an EPROM such as the AT28C64B from Atmel.  Although it has a 13 bit address (A0 thru A12), you would ignore A8 thru A12 (set to zero).  What ever previously written data you have stored in the EPROM representing the HOH data would be output on its data lines D0 thru D7.

     

    I offer this NOT as a system design, nor a product design, but rather a way for you to test out your theory and an easy way to try out alternative HOH data.

     

    Good Luck

    Ken