Re: [Audacity-nyquist] =?iso-8859-15?q?Slider_Bug_Investigations_-_wa?= =?iso-8859-15?q?s=3A_Pluck_in_Audacity?=

[<edg...@we...>]

>From the 'Pluck in Audacity' discussion:

> > Slider Bug:
> > 
> > 1. I generate an Audacity track using 'Tone' from the 'Generate' menu.
> > 2. I mark the whole track.
> > 3. I open the effect window ot the 'Lowpass' filter from the 'Effect' menu.
> > 4. I type into the text box beside the 'cutoff' slider a value of 100 and apply the effect.
> > 5. I re-open the effect window ot the the 'Lowpass' filter again.
> > 6. The 'cutoff' slider now re-appears with a value of 101 instead of 100.
> > This is what I call a 'near-by' value but not 'exactly the same' value.
> 
> Ah yes I have seen this many times, if typing in the number. But if you 
> use the slider to make the setting, the problem does not seem to happen.
> Even if you type in, it does not happen if the number you type is higher. 
> And if I look at say Tremolo, I can't seem to reproduce the problem at all.     
> Does this suggest some kind of rounding problem?

Observation: as long as I only move the slider with the mouse the correct
values seem to re-appear. The bug only start to happen as soon as I type
something into the text box beside the slider.

IMHO the Nyquist effect window slider bug is probably caused by:

file: src/effects/nyquist/Nyquist.cpp
function: NyquistDialog::OnSlider

856:      int val = slider->GetValue();
857:      ctrl->val = (val / (double)ctrl->ticks)*
858:         (ctrl->high - ctrl->low) + ctrl->low;

in line 856 and 857 the value of ctrl.val (the Nyquist slider variable)
gets (at least in my understanding) computed out of the wxWidgets slider
coordinates. This probably worked before the text field beside the slider
was introduced. Values typed into the text field of course don't care
about wxWidgets coordinates (but I have no idea in what precision the
wxWidgets slider->GetValue() will be returned). 'slider' is derived a few
lines above from any wxWidgets code that's beyond my understanding.

> > Duration bug:
>>
> >The duration bug seems to happen in the effect window. If I set the
> > slider to exactly 1.0 the value of the slider Lisp variable, in which
> > the slider value is given to the Lisp program already has a wrong value
> > of 0.997.

I unfortunately still have no idea what the 'Audacity gives wrong variable
values to Nyquist' bug could be.

I just have downloaded a new CVS version and will continue bug tracking.

- edgar



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