Simple first order lpf?

[seyyah]

I'm not famliar with digital filters. I want to implement a simple one to learn. Here is an example:
**broken link removed**

In that, there is a coefficient α, which is obvious, an output, a previous value of the output and an input. I wonder, if i want to apply this how would i decide somethings like;

1-What's the first value of the previous output value?
2-How to decide sampling time or α coefficient in the example?

 

[vadkudr]

>>1-What's the first value of the previous output value?
Of course zero. Imagine you begin process from silence. and after for ex 5 sec of silence you obtain real signal. Zero begin state is commonly used init state


>>2-How to decide sampling time or α coefficient in the example?
You can regard impulse response of this filter (reaction to 1,0,0,0,0,.... sequence)
it will be
1,alpha, alpha^2, alpha^3, and so on
Considering sampling period, you can estimate how long time period covers your filter

 

[haydaa]

you can see at matlab demos more clerly and easyly.