hello, I don't think your probem is with wrap~. if you create a phasor at 25x120 = 3000Hz, using a 44100KHz samplerate, you will notice that all ramp have different amplitude. This is because a ramp have 4100/3000 sample = 14.7 point for each ramp. if you switch to 48KHz, you will have 16 sample per ramp, and all ramp will have the same amplitude. This also create phase isue.
So, I gueess you should use a fps that is compatible with your samplerate. cheers c Le 26/04/2018 à 21:23, Derek Holzer a écrit :
Dear Pd friends, can you help me to understand [wrap~] better? My purpose is to create a "video raster" (using audio signals at a high sample rate) of X and Y values to read luma information from [pix_data]. To do this, I have one [phasor~] creating the vertical ramp, at 25 Hz (= 25 frames per second). Then I require another series of ramps from 0 to 1 for the horizontal lines. If I want 120 lines per frame, I do it like this: [phasor~ 25] | [*~ 120] | [wrap~] This gives me 120 ramps for every one cycle of [phasor~]. So far so good. However, the ramps I get are not equal in amplitude, there are tiny variations which cause distortions in the raster, and which I can see when I plot the ramps to a array with [tabwrite~], and which I can see as a jagged edge if I plot my raster out on an XY oscilloscope or similar. Also, the ramps have some phase issues. 25 frames with 120 lines per frame works just fine, but as I adjust the frame rate or the number of lines per frame, the image data which I get from [pix_data] seems to "rotate" out of the frame and wrap around to the other side. Only multiples of 25/120 give me image date which is centered in the frame of the video or image being analyzed by [pix_data]. I would be happy to make a video of this if you like, but I wonder if someone with better DSP knowledge than me might have some suggestions. You can see the patch in question here: https://github.com/macumbista/vectorsynthesis/blob/master/V-scanprocessor-help.pd (Requires checking out entire Vector Synthesis library. Also requires PD >= 0.47 and Gem if you want all of it to work. Open the [V-scanprocessor] object to see the [phasor~] and [wrap~] configuration.) Andy Farnell suggested that the amplitude differences in the ramps may be a cumulative 32 bit precision error, but that would not explain the phase issue. I also tried using sample-rate [metro] and [line~] objects to create the horizontal lines but this was even less precise. Thank you for your kind attention! Derek
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