I need to identify certain features of the audio signal recorded from microphone in stethoscope. These sounds are only samples i've found, but the final signal will be probably a bit noisier (maybe not, i don't know yet). Below are examples of three signals. Normal one and one of the person sick with atrial spatial defect, third one is of person with late aortic stenosis. These two fluctuations are named S1 and S2 respectively and they are my main subject of interest. Depending on a given heart condition S1 may have doubling and there may be some "noisy" sounds (clicks also) between S1 and S2. The length of the whole cycle (S1, S2) may vary depending on the heart rate.
My question is, what kind of processing should i perform to surely extract and recognize those features, i.e. two large fluctuations normally, with slight delay between them and if person is sick it may be either something before S1 or between S1 and S2 or S1 may double a bit. Also normally S1 has a larger amplitude spike than S2 as i understand.
I have very limited knowledge in this field and not sure about what options are available to me. FFT magnitude graphs are showing somewhat recognizable results, but i think there is too much unneeded information there and they are not so distinct.
The samples themselves can be found here: Washington University: Heart sound samples
Normal heart sound: Atrial spatial defect heart sound: Late aortic stenosis: