0
$\begingroup$

I am new to DSP, I'm trying to implement a low pass filter in a microcontroller and I'm looking for examples on the internet.

One of the simplest low pass filter (as its title says) is this. But I don't understand how is this a low pass filter? All that I see is just an equation

y = 2x - 1

I made a simple example on google sheets and it gave me the same triangle signal with just higher amplitude. What am I missing?

enter image description here

$\endgroup$
2
$\begingroup$

The equation you probably refer to is

$$y[n]=x[n]+x[n-1]\tag{1}$$

(which is not equivalent to $y[n]=x[n]+x[n]-1$).

The integer $n$ is the time index, so from in Eq. $(1)$ the output is computed as the sum of the current and the previous input values. This is, up to scaling, equivalent to a two-point averaging operation. This low pass filter is really quite simple but it also doesn't really do much.

Another very simple but better low pass filter is

$$y[n]=\alpha x[n]+(1-\alpha)y[n-1]\tag{2}$$

which is called an exponentially weighted moving average filter. There are a lot of questions about that type of filter on this site, e.g. here, here, here, and here.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.