A suggestion from Johannes Taelman solved the issue:
"Make sure the number of audio samples used per scanline is a whole number."
Thanks for having a look in any case! Derek
On 25/08/2018 20.44, Derek Holzer wrote:
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.tx...
(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