Perhaps a good place to start is to work out what the aliased value of 3.2MHz 
is - i.e. when you divide 3.2MHz by the number of lines over which the signal 
is spread (625 for the PAL system).
Patch enclosed,
Ed
 
Gemnotes-0.1alpha: Live music notation for Pure Data
http://sharktracks.co.uk/


________________________________
 From: Off Screen <offscr...@personalreport.it>
To: pd-list@iem.at 
Sent: Thursday, 12 July 2012, 18:20
Subject: [PD] Video synthesizer emulation
 

Hello everybody,

I'm trying to emulate an analogue video synthesizer using GEM. My starting 
point is the LZX system, an old school analogue video synth which has been 
rebuilt today using modern circuitry components. Obviously that wonderful tool 
is way too expansive for me so I thought I could build something similar using 
Pd.

My first goal is to succesfully emulate the Video Waveform Generator:
http://www.youtube.com/watch?v=pbpFgvttBZw

Here is a detailed description:
http://www.lzxindustries.net/modules/video-waveform-generator

I've tried to use [pix_sig2pix~], it works quite nicely and the patterns I get 
are almost identical to the ones in the video (including all the fm and pwm 
stuff). The problems are in the second part of the video, when they use high 
frequencies (~ 3mhz) to generate vertical bands. I'm pretty sure I can't use 
the same approach with Pd.

The other option would be to use GLSL shaders, but it has two major drawbacks: 
first, it won't be using raw signal but control messages (no sound generation); 
second, it won't be patchable, once the parameters are converted into an image 
all the informations about frequencies are lost and I won't be able to use it 
to modulate another shader.

I'd like to know from somebody who has much more experience than me what would 
be the best approach. Are there any limitations or constraints within the 
[pix_sig2pix~] object or Pd itself that I should be aware of? Any advice will 
be extremely appreciated.

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