1-pole high pass filter in Lua with VCV Prototype

Development
1

Hi all,

EDIT: edited inquiry to reflect forum structure

I’m having a blast trying out the Lua scripting for the Prototype module. I have very minimal experience with DSP, mostly using Reaktor and JSFX. A question… perhaps due to my lack of familiarity with the VCV Prototype paradigm or DSP in general (I’m very much in the copy/pasting phase).

I hit a roadblock when implementing a 1-pole high pass filter. The last bits are:

lp_outl = 2*filterinput*lp_a0 + lp_outl*lp_b1
filteroutput = (filterinput-lp_outl)*outgain

And I get the following error:

attempt to perform arithmetic on global 'lp_outl' (a nil value)

I presume this is because I am using a recursive definition, but I don’t quite understand the fix.

Additionally, can someone shed some light on when it is appropriate to define variables in the body of function process(block) vs … block.bufferSize do. In JSFX, there is space for performing math on parameters at the control rate vs the samplerate, but I am unclear on where those distinctions lie in the Lua scripting model.

2

On this forum, typically thread topics are questions, and responses are answers or discussions to eventually obtain an answer. I have edited your title to refer to the question at hand.

Did you define lp_outl as a global in your script? Something like lp_outl = 0.0 at the root level of your script?

Code in process() runs every block. Code at the root level of your script runs once when your script is loaded before processing blocks.

3

Edit: saw my mistake.

Yeah, that passes audio for sure. I failed to init that variable in the root level. Thanks.