Conditioning ADMP404 output for ADC

Hi Raj,

Am I correct that you're looking to add 52 dB of gain to the microphone's output so that an 80 dB SPL signal is amplified to 0 dBV (1 Vrms)? Even if you're only intending to capture voice in the typical speech range (60-80 dB SPL), I don't think that you'll want to amplify the signal so that all inputs above 80 dB SPL will be clipped. Even for speech signals with an rms level of 60-80 dB SPL, they may have a crest factor (difference between the rms level and peak level) of 20 dB. This would mean that the peaks of the speech signal could reach 80-100 dB SPL. If you still want to match the peaks of the acoustic signal to 0 dBV, then you'll just need 32 dB of gain. On top of that, if you assume that someone using your design may speak right into the microphone, the input signal could be at an even higher SPL. You may want to configure your design to account for that by using even less gain.

It does look like the SSM2167 would be a good device to pair with the ADMP404. We have a Circuit from the Lab describing exactly this setup (CN-0262). In a voice capture application, the compression and noise gating that the SSM2167 offers may make your captured sound more intelligible by reducing the dynamic range while still applying a reasonable gain. If you just want to use an op amp in a straight amplification circuit, then either the AD8542 or AD8506 should work fine.

Could you explain more about what exactly you're looking for with "noise cancelling"? Are you trying to do acoustic noise cancellation, or are you just looking for a "noise cancelling" microphone with a figure-8 pickup pattern?

Hi Raj,

Am I correct that you're looking to add 52 dB of gain to the microphone's output so that an 80 dB SPL signal is amplified to 0 dBV (1 Vrms)? Even if you're only intending to capture voice in the typical speech range (60-80 dB SPL), I don't think that you'll want to amplify the signal so that all inputs above 80 dB SPL will be clipped. Even for speech signals with an rms level of 60-80 dB SPL, they may have a crest factor (difference between the rms level and peak level) of 20 dB. This would mean that the peaks of the speech signal could reach 80-100 dB SPL. If you still want to match the peaks of the acoustic signal to 0 dBV, then you'll just need 32 dB of gain. On top of that, if you assume that someone using your design may speak right into the microphone, the input signal could be at an even higher SPL. You may want to configure your design to account for that by using even less gain.

It does look like the SSM2167 would be a good device to pair with the ADMP404. We have a Circuit from the Lab describing exactly this setup (CN-0262). In a voice capture application, the compression and noise gating that the SSM2167 offers may make your captured sound more intelligible by reducing the dynamic range while still applying a reasonable gain. If you just want to use an op amp in a straight amplification circuit, then either the AD8542 or AD8506 should work fine.

Could you explain more about what exactly you're looking for with "noise cancelling"? Are you trying to do acoustic noise cancellation, or are you just looking for a "noise cancelling" microphone with a figure-8 pickup pattern?