noise on analog inputs.

simonb

Hi,
I have wired up some Phototransistors to my Bela mini analog inputs I am getting some predictable good results but quite a few spikes. See the screenshot below. low light should give me 0.00123 etc. High light 0.1 ++ Thats great when it works, but I get crazy spikes of 5, 6 7 etc. So I guess my question is.. do you always need to software filter to get rid of these. I noticed a C++ example where you do this.

I was actually trying to use SuperCollider and getting the same results as this PD example and finding it pretty hard to filter it.

Any tips would be really welcome.

Many thanks

Simon

simonb

Amazingly, In a strange late night twist ChatGTP seems to have solved it for me in SuperCollider.
Is this sort of filtering pretty standard then?

(
SynthDef("AnalogInputs",{ arg inPin=0;
var input0 = AnalogIn.ar(inPin);
input0 = Lag.ar(input0, 0.1); // Smooth input with a short lag
input0 = input0.clip(0.0001, 0.3);
SendReply.kr(Impulse.kr(10), '/input', input0);
}).add;

giuliomoro

Those are not high spikes. They are very small numbers written in scientific notation.

simonb

Ah ok.... Thanks. I thought it might be something like that. The code above seems to clear them out of the way so I think its ok.

Cheers

giuliomoro

Filtering is a normal way to reduce noise in analog inputs, but that's not what "fixes" your issue: low pass filtering wouldn't prevent it from showing those small values. What is preventing it from showing those small values is the clip(0.0001, 0.3), which limits the bottom of the range to 0.0001, which is large enough to be printed in standard notation and not in scientific notation. This is not just pointless, but actually harmful because it limits your range to between 0.00001 and 0.3 just to solve what is ultimately a visualisation issue. If you are annoyed by those small values being printed that way, filter them off in the printing and not in the signal path.

simonb

Thank you... that makes sense