Thanks a lot for the recommendation, I got it working and am and onto the next challenge!

@whale-av said:

@Digital-Larry [edge~] will bang on zero crossings and give direction.
[change~] [xerox~] and [expr~] are also useful.
David.

@whale-av I am not finding [edge] or [edge~], is that in pd-vanilla or pd-extended?

I have vanilla installed at the moment. Thought I read that extended wasn't being maintained? Is it possible to have both installed at once?

Update - I cascaded 2 snapshot~ objects driven from a 40 msec metro object and subtract the outputs from each other - this appears to align zero crossings with the LFO peaks. Now I just have to detect zero crossings and generate a bang when that happens.

Thanks for the responses.

Although I've messed with pd a bit in the past, I'm just picking it back up now with an actual concept of what I want to do. I did try the rzero object (real zero, FIR filter) and as you can imagine, the sample to sample difference of a 10 Hz sine wave is exceedingly small and when multiplied by 100000 or so, looks like we might be exploring some sort of quantization limit because "theoretically" I would expect that to be smooth, with a sine wave input. However, it is very spiky.

My LFO is built by summing two sine waves of (different) variable frequency and so, actually I don't know ahead of time when they will switch direction but I'll look at that vline object anyway.

I also thought about having something like two daisy-chained 5 msec delays and comparing those outputs, or subsampling the LFO some other way because I don't need audio sample resolution, I think 10-15 ms would be fine for this. I'm sure there's something obvious I haven't stumbled across yet.

I'm looking for a way to generate a bang when my LFO signal changes direction. Something in my distant memory leads me to think this could be accomplished using the second derivative of the LFO signal and looking for zero crossings.

I looked on here for "derivative" and found a couple posts about ten years old. I also seem to remember that a high pass filter is a "differentiator" but certainly the corner frequency must get involved in some important way. If I had a delay line with 2 taps coming out I'm pretty sure I could generate something suitable.

Any suggestions?