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Waveforms 3.18.1 AWG SinePower setting lost


Rick314

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To replicate this start Waveforms 3.18.1, choose instrument Wavegen, Type: SinePower, Power: -99.  See the given image. Change "Type:" to Sine and back to SinePower. The "Power:" setting is reset to 0 instead of staying at -99, producing a normal sine wave instead of the SinePower pulses. I think the -99 value should be maintained so I don't have to re-enter it after every change to Type.  Is this a Waveforms defect?

SinePower.PNG

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Hi @Rick314


Below is an animation of the behavior off the supported AnalogOut waveforms as a function of the 'symmetry' parameter:

waveforms.gif
As you can see, the "SinePower" is the only waveform shape that exhibits any shape changes when its 'symmetry' setting dips below zero.

My assumption is that the Waveforms software, upon changing to a shape other than SinePower, ensures that the value will be non-negative.

Whether that's a bug or not I'll leave to people from Digilent, but to me at least the behavior is somewhat understandable, given the fact that the SinePower waveform shape is a bit of an odd one out.


 

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Thanks reddish, but based on the user interface SinePower doesn't have a "Symmetry" setting.  It has a "Power" setting instead. Also now I see this is a user interface sequence dependency -- Changing Type always resets Symmetry or Power to a default value.  For example: Sine, Symmetry to 75%, Square. Symmetry gets set back to 50%. So it appears "Power" and "Symmetry" are two names for the same setting, that gets reset to default on each Type change.

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They are indeed one and the same setting.

I figured out the definitions of all defined wave-shapes at some point (which is how I made the animated GIF).

In the software API that you can use to control the devices (and that the Waveform application is built on), there is a single parameter that influences the shape of periodic waves. This parameter is called "symmetry" in the API but, in the case of the SinePower shape, this number is used to calculate an exponent value that is used to calculate "sin(x) ** exponent", hence the name power in that case. For details, see this Python code, around line 150.


I agree that it's all pretty confusing.

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I think this is a user interface defect and worse than the thread title implies.  A better title would be "Symmetry changes value when 4+ related settings are maintained".  As an example set Type = Sine and change Frequency, Amplitude, Offset, Symmetry, and Phase (5 details of Sine).  Change Type to Square.  All 5 detail settings are maintained except Symmetry and it changes to 50%.  Symmetry should maintain its value like the other 4 settings do.

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I mostly agree, although the fact that the sine-power is the only wave-shapes where a negative "symmetry" value makes sense complicates matters a bit -- it is not entirely clear how to handle switches between all settings, in all situations, without ever surprising the user.

Let's see if anyone working for Digilent agrees and is willing to consider making a user interface change.

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SinePower "Power" has range -100 to 100 (correct) and other waveform Types have "Symmetry" with range 0 to 100 (correct). "Power" and "Symmetry" are different settings with different ranges.  The issue I want to focus on is that both Power and Symmetry get initialized (rather than being maintained) when "Type" is changed.  This is inconsistent with at least 4 other related settings.

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> "Power" and "Symmetry" are different settings with different ranges.

Except that they are not, internally; so that's a complicating factor. Whenever there is a discrepancy with how things work deep down, vs how things are exposed to the user in the GUI, something has got to give, and it will be hard to make the GUI behave in a way that is fully intuitive all the time.

Anyway, I hope someone of the Digilent team will show up.

Edited by reddish
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Thanks atttila and I see now that no single default Symmetry value makes sense for all AWG signal Types.  But I think a better implementation would have been a separate Symmetry (or Power) setting for each Type.  That way they could have different default values and switching from Type A to B to A would yield the original A waveform.  Are there issues with this approach?  (I'm not saying it should change now, just discussing if that would have been a better initial implementation.)

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