Track and Hold Unit

Hi Brian,

I’ve been fiddling today with the track and hold and sample and hold units… and I still can’t get the T/H unit to behave any different.

I know that the S/H circuit ‘samples’ the input the moment you trigger it and holds it at that sampled level. This unit works as expected.

From my understanding, the Track/Hold should allow the input signal to flow through normally (the “track”) but then “hold” the voltage the moment the gate goes high… and then return to ‘tracking’ when the gate input goes low.

such as this crude diagram I made below:

If this is the case, then currently the Track and Hold Unit isn’t (but should be) passing CV through when the gate is low. And, the ‘trig’ input acts as an instant blip vs. being held closed as long as there’s a gate Hi signal. (suggest renaming this ‘gate’).

So, with these two factors I can’t seem to make it behave any differently than the S/H unit.

Am I approaching this one the wrong way?

Your description sounds right to me, the diagram is a little confusing as I would expect the gate to be high when hold is activated. I get it though :slight_smile:

I just tried and couldn’t get this to work either :slight_smile:

I just made a crude diagram and edited my post :slight_smile:

That’s much clearer and yep - that’s what should happen!! :slight_smile:

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Neil your approach looks correct.

I haven’t been able to get this unit to work either.

:bow: For some reason, in the mono version of the T&H, I have a gate to trigger converter in front of it. Really sorry about that. The stereo version is fine but of course you would probably never use this unit in stereo. I’ll have this fixed in a few days.

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No need for apologies as far as I can see, we’re riding an untamed beast at full speed ahead!

These things are inevitable when working with a large code base… :nerd:

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Aaaah! Well that explains it as I’ve only ever tested it in mono.

Glad it’s on the list, no need to apologize!

When a gate signal goes high at the T+H input the functions output will track the input signal. When the gate signal goes low at the T+H input the functions output will hold the last sampled signal. Your drawing has this flipped.

Yes I realized this now. Whoops!

Huh… I thought we had the drawing correct?

I’m confused now, the way you explained it in your first post seems right to me - gate high the input is sampled and held at that value - gate low, the original input passes through.

Does the unit work the other way?

yes - currently backwards to my crude diagram. But honestly, i don’t have a track and hold module, so i was just basing it on probable misinformation :smiley:

Oh, ok… that’s weird!! Got that completely the wrong way round, just checked the Doepfer A148 and it’s that way round too!!

http://www.doepfer.de/a100_man/A148_man.pdf

I think I did the same, but it’s strange, I don’t see why it would be that way round, surely it’s much better more useful to hold on the rising edge of a gate?

That would be a hold and track which might also be useful.

S&H: sample on the rising edge, otherwise hold the last sampled value.
T&H: track on high, hold on low.

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+1 if you could add the hold and track to a raining unit to-do’s list!

I could see both being interesting for IE: arpeggiator CV and creating some interesting musical results with various clock timings! :slight_smile:

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The diagram for the A148 is for the Sample and Hold Circuit

Agreed!! :smiley:

The Doepfer manual doesn’t have a diagram for the T&H, it’s in the description:

In T&H mode the output si- gnal follows the input signal while the trigger input is “high”. As soon as the trigger input turns to “low” the last voltage is stored.

One application of this arrangement is to track modulation while interacting with a controller (e.g. keyboard, faders) and to hold off on the modulation while the controller is at rest. That’s not to say this is more useful than the other way around.

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Not finding the Track and Hold unit listed in the Wiki’s Known Issues and Feature Requests Tracker, will this unit join the ranks at some time in the future?

It’s already in there - right next to the Sample and Hold :wink:

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