Can someone explain about digital filters

[and-sh]

Pt1 low pass filter is simple iir filter
It defined by following equation
out=in * alpha+out * (1-alpha)
At sampling rate 2kHz and bandwidth about 100Hz alpha is about 1/4.

So 1/4 of 'in' is always translated to out.
This means that it can suppress noise only 4 times no matter of it frequency?

[and-sh]

some pictures
white noise source instead one gyro

After all filters

Moving averaging 14pts about 6kHz as aa filter

after all filters

[and-sh]

frequency and step response
red - unfiltered
blue - pt1 100Hz
green - moving average 7pts
pink - biquad 150Hz

pt1 & pt1 + 3 notch