script.crossfaderCurve does not work as desired

[mixxxbot]

Reported by: daschuer
Date: 2015-08-06T10:17:30Z
Status: Confirmed
Importance: Medium
Launchpad Issue: lp1482163

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The code implies that we are able to tweak the xFader independently for each mode.

script.crossfaderCurve = function (value, min, max) {
    if (engine.getValue("[Mixer Profile]", "xFaderMode")==1) {
        // Constant Power
        engine.setValue("[Mixer Profile]", "xFaderCalibration", script.absoluteLin(value, 0.5, 0.962, min, max));
    } else {
        // Additive
        engine.setValue("[Mixer Profile]", "xFaderCurve", script.absoluteLin(value, 1, 2, min, max));
    }
}

Unfortunately the slider in the xFader preferences tweaks xFaderCalibration and xFaderCurve in both modes.
Tweaking the modes independently seams to be desirable. So I consider the CO interface and the preference dialog and the underlying calculation as broken.

[mixxxbot]

Commented by: daschuer
Date: 2015-08-06T10:22:06Z

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If we fix this this, it should be easy to fix Bug #⁠829538 as well, by shifting the maximum towards a steep cut.

IMHO this is a 1.12 bug, and it should be fixes without any interface changes.

Thoughts?

[mixxxbot]

Commented by: daschuer
Date: 2015-11-27T12:10:00Z

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xFaderCalibration is used in both modes.
The range is now 1 ... 1000

[mixxxbot]

Commented by: daschuer
Date: 2016-01-21T20:17:15Z

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Please note: the xFaderCalibration depends on the value of xFaderCurve to achieve a desired curve.

Fading:
xFaderCalibration 0.5 / 0
xFaderCurve = 1 / 0
Scratching:
xFaderCalibration 0.999307 / 0.998614
xFaderCurve = 1000 / 1

See:

mixxx/src/engine/enginexfader.cpp

Line 10 in d46433b

double EngineXfader::getPowerCalibration(double transform) {

xFaderCalibration = pow(0.5, 1.0 / xFaderCurve);

[mixxxbot]

Commented by: kejbilgsf
Date: 2016-02-22T03:48:56Z

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Maybe this comment will be helpful:

mixxx/src/preferences/dialog/dlgprefcrossfader.cpp

Line 203 in 479c9e1

// m_transform is in the range of 1 to 1000 while 50 % slider results

So, the xFaderCurve is in the range of 1 to 1000 while 50 % slider results to about 2, which represents a medium rounded fader curve.