. Also, I will be using electret microphones with breakout board (MAX4466) which has op amp if I'm not mistaken
I'm working on a proposal project about digital stethoscope
I'm not sure why noise reduction is necessary. A regular acoustic stethoscope doesn't have noise reduction.
Regular high-pass, low-pass, or notch filtering can work if the noise has an identifiable frequency. This can work especially well if the noise is outside of the signal-frequency range. For example, a low-pass filter can remove 50/60 Hz power line noise from a voice recording without affecting the voice.
So with Band-Pass filter, can I remove the ambient sound and heart sounds?
but do I need to implement Noise Reduction so that the data can be analyzed by the AI?
I would suggest you look for at least a 6th order filter here
Note if the background noise is in the same frequency range as your wanted signal this will do no good at all.
If you are not using your data to train an AI system but a standard data base then implementing a filter or noise canceling algorithm is going to produce better results than not doing anything.
I am assuming you have an oscilloscope, it would be fruitless to attempt a project of this nature without one.
Get as much as possible working the easiest way you can, with large known-good shields or breakout boards, before you dive into shrinking the size or designing sensitive analog circuitry.
If using such a breakout board or shield which already has all the analog circuitry done and delivers digital data, I can't understand why a 'scope would be used at all.
If you use a board and library with I2S support, you might consider a microphone with all-digital I2S output.
Why is an oscilloscope needed?
Sure, you can see the signal
The ideal tool is a dynamic signal analyzer (aka FFT analyzer) or audio analyzer,
Can I just run an FFT algorithm to see the frequency wave?