[AudioI] Advice for low-frequency project

[John McManigle]

Hello all,

I am working on a project to record/analyze low-frequency noise with a Pi Zero. Currently early in the prototyping stage, so want to see whether this plan seems feasible:

ICS-40300 analog MEMS microphone (which has extended low-frequency response), planning to use the pre-fab test board (https://www.mouser.com/ProductDetail/410-EV_ICS-40300-FX <https://www.mouser.com/ProductDetail/410-EV_ICS-40300-FX>) during prototyping.
	which would connect to...
I guess would need a custom op-amp circuit to go from mic level to line level (looks like that mic outputs at 0.355 Vrms at 200Ω impedance; not sure how close that is to line-readable).
	which would feed...
The line input on a Audio Injector Zero Sound Card. (Planning to use line in even if it needs amp rather than mic input because future versions might require two channels.)

I am pretty comfortable with basic digital work and programming, but this is one of my first forays into the analog world. So my questions are:

1. Does this seem like a reasonable approach overall?
2. Does anyone know of a MEMS microphone with extended low-frequency response that outputs I2S or otherwise digital, as that would save some design headache obviously? (My target sounds are 20-150 Hz.)
3. Is there a built-in highpass filter in the Audio Injector Zero card that would limit input performance in the 20-150 Hz range?
4. Any recommendations on the mic-to-line amp circuit? I was planning on approximately following https://www.st.com/resource/en/application_note/an4598-preamplifying-the-analog-output-of-a-mems-microphone-stmicroelectronics.pdf <https://www.st.com/resource/en/application_note/an4598-preamplifying-the-analog-output-of-a-mems-microphone-stmicroelectronics.pdf>
5. Other general advice?

Thanks very much,

John


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