ADMP441, SSM2529 Speech transmission

I am constructing a hearing aid for my bachelor degree project. This hearing aid will consist of a microphone with a Nordic Semiconductor nRF2460 2.4 GHz transmitter, and a receiver of samë model with a speaker. This device should filter out any unwanted frequencies outside of speech, that is anything outside of 1-5 kHz. We want to sample at 12 kHz. I and my group are designing the PCB's and power supply ourselves. For simplicity we want mostly digital signals on our PCB's. Therefore we want to use the ADMP441 which has an ADC included with an I2S interface. Our transmitter and receiver (which are the same IC), support 16 bit I2S. The SSM2529 will be our DAC and amplifier stage, and also the filter stage.

The question is, can I use the ADMP441, which supports 24 bit, to send a 16 bit signal to my 16 bit compatible transmitter?

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  • The ADMP441 will always output 24-bit audio data. This may be compatible, though, with your transmitter's I2S input. The transmitter may be able to just use 16 of the 24 bits that it receives from the microphone. I looked at the nRF2460 data sheet to see if there were any issues with this interface and I wasn't able to find all of the information that I needed about it's I2S input. In I2S mode, the nRF2460 will be compatible with the ADMP441 as long as it is generating an SCK signal that is always 64x the rate of WS (sampling frequency). The nRF2460 data sheet is not clear on what the rate of its CLK pin is in master mode. If you determine that it will output a CLK at 64x fs, then the ADMP441 will work fine for your application.

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  • The ADMP441 will always output 24-bit audio data. This may be compatible, though, with your transmitter's I2S input. The transmitter may be able to just use 16 of the 24 bits that it receives from the microphone. I looked at the nRF2460 data sheet to see if there were any issues with this interface and I wasn't able to find all of the information that I needed about it's I2S input. In I2S mode, the nRF2460 will be compatible with the ADMP441 as long as it is generating an SCK signal that is always 64x the rate of WS (sampling frequency). The nRF2460 data sheet is not clear on what the rate of its CLK pin is in master mode. If you determine that it will output a CLK at 64x fs, then the ADMP441 will work fine for your application.

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