[sdiy] video thru a spring reverb?

[Grant Richter]

> The device I built uses a phase locked video synch generator, LM318  
> op-amps and solid state switches to format any signal to video  
> standards.
>
> The RGB standard is basically from +100mv. to +1.0 volt only during  
> non-blanking and non-synch intervals. The op-amps negative clip the  
> signals and the synch generator only turns the solid state switches ON

Correction: The solid state switches are turned OFF during non- 
blanking, and ON during blanking. That effectively shorts any signal  
to ground. The signal actually goes from about +100v to +700mv. The  
total amplitude is 1 volt peak to peak with 300 mv. of synch and 700  
mv. of signal.

> during non-blanking times. RGB signals are the same as three black  
> and white signals (with no color sub-carrier on 3.58 mHz). When the  
> color sub-carrier is added it is called "composite" video. A black  
> and white video signal doesn't have the 3.58 mHz color sub-carrier.
>
> Synch (-300mv) and blanking (0 volts) are "forced" onto whatever  
> signal is input to the RGB inputs before being sent to the RGB to  
> NTSC encoder.
>
> There is a method called a "back porch clamp" which is used to DC  
> restore AC coupled video. It is a 0.1 uf cap followed by a solid  
> state switch to ground, and an op-amp unity gain follower. The  
> switch is normally driven by a clamping signal/burst gate from an  
> LM1881 or similar synch chip.
>
> I made the drive signal to the solid switch "NOT-blanking"

Correction: Blanking drives the switch to short the signal to ground  
instead of passing it through the cap to the op-amp.

> and added a diode to the unity gain buffers so they only go  
> positive. That allows the external RGB signals through only during  
> non-blanking times and keeps them out of the negative synch region.
>
> On Aug 8, 2006, at 3:23 AM, denshi wrote:
>
>> on grant's paia page he shows some video effects done
>> with his paia modular.  maybe grant or someone on this
>> list could go into greater detail about how this is
>> accomplished?  im particularly interested in spring
>> reverbing a color seperated from a video signal
>>
>> thanks!
>> seth
>>
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