[PD] oscilloscope raster with audio signals

Derek Holzer macumbista at gmail.com
Sat Aug 25 20:06:33 CEST 2018


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.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



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