Sample and Hold


#1

I am curious if patching a video signal into an audio rate sample and hold module will compromise the quality of the output signal, as would happen when using an audio rate vca or filter?


#2

Yes, most Sample & Holds are very slow for video. We got one working at one point, but could not get better than 10-20 pixels of slew on the edges. I think we determined that this feature was best saved for a digital processor, where you can do it based on keying and compositing to freeze/unfreeze parts of the image.

Where sample and hold does come in super useful is with frame rate/animation stuff. If you’re using a square wave LFO for example, you will be familiar with mid-frame glitches in the image when it switches. By sample and holding that square wave and triggering sample and hold with the Frame rate sync output, all those switching glitches will disappear.

War Of The Ants has two sample and hold circuits! The noise is ran thru a S&H triggered by hsync before the vertical filter. It is ran thru a S&H triggered by vsync before the animation/slew circuit. It’s an interesting use case where we’re using sample and hold to confine the noise to different frequency domains before they are processed and then recombined.


#3

Thanks for the informative reply! So, even though War of the Ants has two S&H with H/V ins and outs, it is still unable to render the results noted above (grab bits and pieces / frames of an image)? Will this be possible with the addition of Memory Palace or would there be a need for an isolated video rate sample and hold with an integrated frame buffer (possibly as mentioned with an upcoming sampler/looper module)?


#4

Here’s some old footage of the original video rate sample and hold circuit I was talking about:

As you can see, there’s a fuzzy area between transitions that limits performance. Is this the kind of effect you are wanting? Memory Palace does a mosaic mode (H/V pixel resolution reduction) that is a similar effect. And you can also key between a frozen image in the buffer and the incoming stream, which is also a similar effect. In general, I would think a frame buffer as a very advanced form of sample and hold, but there may be a place for a more analog look like the module above.


#5

this looks like castles… maybe with castle shift register or flipflops (both are sort of s&h) would work.


#6

Yes, it’s kind of an analog bit rate reducer! The difference is that you are holding an analog voltage instead of a 3-bit value with 8 levels.


#7

then a Castle DAC fed into a Castle ShiftR/Flipflop should do the trick.

the dac generates a 3bit (8 level) analog signal fed into a clocked castle


#8

Yes, but it won’t be the same effect as an analog sample & hold since you’ll only have 8 possible grayscale values to sample and hold rather than the continuous analog domain. Still will look cool though. :slight_smile: Fortress has a shift register mode as well.


#9

ADC D0-D2> Flip Flops D0-D2> DAC D0-D2> is an 8 level sample and hold, essentially.
Same results as the posted video, but of course only 8 levels as opposed to analog.
With the positive attribute of being able to clock it much higher