1U Noise Tools Sample & Hold inaccurate pitch sampling

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MikeLeeBirds
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1U Noise Tools Sample & Hold inaccurate pitch sampling

Post by MikeLeeBirds » Thu Feb 07, 2019 3:14 am

When sampling pitch CV the tuning is slightly off.
Any idea why?
Is my module broken or might I be doing something wrong?

The Doepfer A-148 S&H samples the pitch correctly, so I assume something’s not quite right with the s&h on the Noise Tools.

Or is this the scenario described in the Shifty manual where the pitch is being sampled a bit too early and a gate delay function would be needed (as exists on Shifty)?

I delayed the sample trigger through Maths, but the sampled pitch (or rather its output) is always a bit too low.
So I assume that the Noise Tools lowers the sampled pitch voltage ever so slightly.


Here‘s the explanation from Shifty‘s manual:

„Sampling Delay Compensation
Due to the nature of how many Eurorack sequencers or MIDI interfaces are implemented their
CV output can lag their gate output by up to a few milliseconds. The consequence is that if a
module like Shifty samples its CV input immediately upon receiving a gate it may read a value
that is slightly higher or lower than that which the sequencer is outputting. If this CV is
being used to control the frequency of an oscillator it will result in it sounding out of tune.
In the case of Shifty if the module is being used in track & hold mode mode this is rarely a
problem because this behaviour will simply result in a short and usually inaudible pitch glide at
the beginning of the note. However in sample & hold mode if the CV is sampled too early, the
note will be slightly out of tune.
Fortunately Shifty provides a way to compensation for this via a configurable gate delay. With
the gate delay disabled the CV output for the selected voice will reflect the CV input as soon as
possible. With the gate delay enabled the CV output and its corresponding gate will have a
slight delay before updating. This allows the incoming CV to settle at its target value.“

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Post by jamos » Thu Feb 07, 2019 10:41 am

What manufacturer? The Pulp Logic S&H seems to have horrible accuracy and droop (no experience, there's a video out there demonstrating this.)

[Edit] Umm, no idea how I completely missed the name of the manufacturer in the subject... move along please...
Last edited by jamos on Thu Feb 07, 2019 5:16 pm, edited 1 time in total.
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intellijel
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Re: 1U Noise Tools Sample & Hold inaccurate pitch sampli

Post by intellijel » Thu Feb 07, 2019 12:31 pm

Noise Tools is %100 analog S&H and is a pretty classic/typical S&H circuit design.

The sampling period is a very narrow window of time where you are tracking the pitch source and then it is held when the trigger pulse goes low.

If you are sampling pitch from a digital source (e.g. sequencer) then it is possible there is some delay between the clock/trigger of the sequencer and the stable pitch value. Especially true if there is any kind of slew on the signal.

Shifty does indeed have functionality built in for gate delay compensation. Scales also has this feature and so you can use it as a quantized S&H which is pretty handy.


*Side note: if you own a Shifty, make sure you updated the firmware! We released a few tweaks a few months ago on our website. Easy to update via USB on back.

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MikeLeeBirds
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Post by MikeLeeBirds » Thu Feb 07, 2019 3:40 pm

I delayed the gate through Maths incrementaly, but the tracking stayed off.
I do own Scales and Shifty, but had hoped that Noise Tools would do this specific job.
Interestingly the sampling is fine with the Doepfer 148, which I assume is analog, too.

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Mungo
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Post by Mungo » Thu Feb 07, 2019 8:30 pm

MikeLeeBirds wrote:I delayed the gate through Maths incrementaly, but the tracking stayed off.
I do own Scales and Shifty, but had hoped that Noise Tools would do this specific job.
Interestingly the sampling is fine with the Doepfer 148, which I assume is analog, too.
You've done some good experiments so far. The usual trouble shooting for pitch CV issues is to try adding a buffered multiple. Try adding one between the pitch source and the S/H and compare the results of the two different S/H units. Then try each one between the output of the S/H and the oscillator.

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cg_funk
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Post by cg_funk » Thu Feb 07, 2019 9:40 pm

Yep, have the Noise tools, and I experience the same problem... The slew input sounds fine for me, but if I patch the V/oct signal through the S+H everything sounds out of tune, and it also droops voltage really fast. Because of this I use it as a S+H only prior to quantization, it's just analog and goofy like that.

I use a Mimetic Sequent as a S+H if I want to hold a note for a long time, and it seems to never fail me for this being digital.
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Post by MatthieuRanc » Mon Feb 11, 2019 10:42 am

Got my Noise Tools on Friday and experienced the same thing… :( Would need to spend more time with it and see what I can do. Maybe tune the oscillator after the S&H with the other voices of my rack…

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