[PD] oscilloscope raster with audio signals

[Derek Holzer]

Dear Pd folks,

I've written about this before here, and I still have not found a 
solution. I've been chasing the same bug in my Vector Synthesis code for 
a year now. The purpose of this code is to draw a "video raster" on an 
X/Y oscilloscope screen with audio signals from a DC coupled MOTU audio 
interface. The brightness of this raster will be modulated by 
information from [pix_data]. Because I am redrawing the raster from 
scratch and the pix information is not tied to the video frame/line rate 
at all, this raster can be of arbitrary frame rate and line numbers 
which remain within audio range. This part works fine and I have no 
questions about that.

My problem is with creating the raster. No matter how I create my raster 
signals, I get the same phase-related offset on my horizontal lines. The 
amount of offset is dependent on the relationship between the vertical 
and horizontal rate. You can see this in the video linked at the bottom 
of this email. Please view that before posting any replies.

The Pure Data patch I am using, which includes three different equally 
flawed methods of making this raster, is available at:

http://macumbista.net/wp-content/uploads/2018/08/oscilloscope-raster-test.txt

(Change .txt extension to .pd)

Video demo is here:

https://vimeo.com/286687337/0b865bd76c

I'm guess there is something in the DSP that I have overlooked. I'm also 
guessing it will take some kind of guru to work it out. If you think you 
are that guru, please let me know.

Thank you for your kind attention,
Derek
-- 
derek holzer
noise.art.technology
http://macumbista.net