Simple test

Vc = 4.5
Rl = 10 kOhm
RC lowpass directly on Vo (Vd)
R = 10 kOhm, C = 10 uF
Analog Discovery II
Jens is whistling without directly blowing in the mic

Setup

Real life

Analog Discovery II measurements

a title says

Whistling by Jens less than 50 cm away

Whistles without blowing in mic
100 mV pp
no viewable noise
“DC” shift up and down every 10 msec (100 Hz) from 50 Hz 230V installation ???
Should we high pass filter away 100Hz and lower?
Should we build a better mockup ? :-)

Rl = 10 kOhm
AC Rl peak-pek == Id peak-peak = 0.1V/10k = 10^-4 A = 100 uA
Remember Id (10kOhm) DC is 213 mA
AC versus DC is 100 uA / 213mA = 1 to 2000 ! in this case
- remember sound pressure can be much lower and higher

So signal variations is very small compared to static setup

Clapping hands 0.5 m

Vpp 600 mV

50 Hz noise

breadboard is crap.
too much 50 Hz compared to whistle above
conclusion: bad measurememt

No signal
A silent as it can be in my humble office
still weird 50 Hz square wave