Effectparameter Scaling

On This page we collect all issue and ideas about Scaling of Effect Parameter.

Controls

Hardware Solutions

Stomp Boxes / DJ Mixer

Rotary Potentiometer
Slider Potentiometer
Rotary Step Switch
Rocker Switch (2 or 3 steps)
Slider Switch
Pushbuttons

DJ Consoles

Rotary Knobs with Midi or higher resolution
Endless Rotary Knobs (Up/Down commands)
LED Row for Feedback
Pushbuttons

Parameter Examples

Gain
Center/Cut-off Frequency
Mode Switch
Periods
Bits
Rate

Desired Scales / Behaviors

Linear
Logarithmic
Audio-Taper
Steps
Split Scale
Pushbutton
Togglebutton
Latching button
Powerwindow button

LV2

http://lv2plug.in/ns/lv2core/

Parameters are "Class lv2:ControlPort" they have a value of c type float.

Example of a ControlPort:

[
  a lv2:ControlPort, lv2:InputPort;
  lv2:index 1;
  lv2:symbol "balance";
  lv2:name "Balance";
  lv2:minimum -1;
  lv2:maximum 1;
  lv2:default 0;
  lv2:scalePoint [ rdfs:label "Left"; rdf:value -1 ];
  lv2:scalePoint [ rdfs:label "Right"; rdf:value 1 ];
],

Additions for Mode Switches:

lv2:enumeration

" Indicates that a port's only reasonable values are the scale points defined for that port. A host SHOULD NOT allow a user to set the value of such a port to anything other than a scale point. However, a plugin MUST operate reasonably even if such a port has an input that is not a scale point, preferably by simply choosing the largest enumeration value less than or equal to the actual input value (i.e. round the input value down). "

lv2:integer

" Indicates that a port's reasonable values are integers (eg. a user interface would likely wish to provide a stepped control allowing only integer input). A plugin MUST operate reasonably even if such a port has a non-integer input. "

lv2:toggled

" Indicates that the data item should be considered a Boolean toggle. Data less than or equal to zero should be considered "off" or "false", and data above zero should be considered "on" or "true". "

lv2:sampleRate

" Indicates that any bounds specified should be interpreted as multiples of the sample rate. For instance, a frequency range from 0Hz to the Nyquist frequency (half the sample rate) could be requested by this property in conjunction with lv2:minimum 0.0 and lv2:maximum 0.5. Hosts that support bounds at all MUST support this property. "

VST

VST uses C Float parameter.

They work on the float range of 0.0f to 1.0f for the value of the parameter. Required scaling should be done inside the PlugIn

/* this struct taken from http://asseca.com/vst-24-specs/efGetParameterProperties.html */
struct _VstParameterProperties
{
   float stepFloat;
   float smallStepFloat;
   float largeStepFloat;
   char label[64];
   int32_t flags;
   int32_t minInteger;
   int32_t maxInteger;
   int32_t stepInteger;
   int32_t largeStepInteger;
   char shortLabel[8];
};

/* this enum taken from http://asseca.com/vst-24-specs/efGetParameterProperties.html */
enum VstParameterFlags
{
  kVstParameterIsSwitch = 1 << 0, /* parameter is a switch (on/off) */
  kVstParameterUsesIntegerMinMax = 1 << 1, /* minInteger, maxInteger valid */
  kVstParameterUsesFloatStep = 1 << 2, /* stepFloat, smallStepFloat, largeStepFloat valid */
  kVstParameterUsesIntStep = 1 << 3, /* stepInteger, largeStepInteger valid */
  kVstParameterSupportsDisplayIndex = 1 << 4, /* displayIndex valid */
  kVstParameterSupportsDisplayCategory = 1 << 5, /* category, etc. valid */
  kVstParameterCanRamp = 1 << 6 /* set if parameter value can ramp up/down */
};

Mixxx

All Parametes in Mixxx are of C Type double.

Mixxx uses the scaled "value" for it's double controls. It is Converted into a parameter, a linear representation of the position on the scale by control behavior classes.

If the value of the control does not match the value that should be indicated in LDS, a separate indicator control is used.

Parameter Hints

class EffectManifestParameter {
  public:
    enum ValueHint {
        VALUE_UNKNOWN = 0,
        VALUE_BOOLEAN,
        VALUE_INTEGRAL,
        VALUE_FLOAT
    };
    
    enum ControlHint {
        CONTROL_UNKNOWN = 0,
        CONTROL_KNOB_LINEAR,
        CONTROL_KNOB_LOGARITHMIC,
        CONTROL_TOGGLE
    };
    
    enum SemanticHint {
        SEMANTIC_UNKNOWN = 0,
        SEMANTIC_SAMPLES,
        SEMANTIC_NOTE,
    };   
       
    enum UnitsHint {
        UNITS_UNKNOWN = 0,
        UNITS_TIME,
        UNITS_HERTZ,
        UNITS_SAMPLERATE, // fraction of the samplerate
        UNITS_BEATS, // multiples of a beat
    };
    
    enum LinkType {
        LINK_NONE = 0, // Not controlled by the super knob
        LINK_LINKED, // Controlled by the super knob as it is
        LINK_LINKED_LEFT, // Controlled by the left side of the super knob
        LINK_LINKED_RIGHT, // Controlled by the right side of the super knob
        LINK_LINKED_LEFT_RIGHT, // Controlled by both sides of the super knob
        NUM_LINK_TYPES
    };
    
    ...

Requirements

Value feedback including units
Control a quantization Value with a continuous Knob
Feedback of the Snapped value
Controllable by Super knob
Support all hardware controls on a DJ Console
Continous Knobs
Endless knobs
Pushbuttons
Allow native adaptation of LV2 PlugIns
Allow native adaptation of VST PlugIns
Control different common scales including Split scales for asymmetric knobs

Links

Related Bug: https://bugs.launchpad.net/mixxx/+bug/1378195
Remove of value hint: https://github.com/mixxxdj/mixxx/pull/356
EQ Rack: https://github.com/mixxxdj/mixxx/pull/297
Button Parameter: https://github.com/mixxxdj/mixxx/pull/281
Kill Buttons: https://github.com/mixxxdj/mixxx/pull/297

Proposed Solution

Nicu has proposed a solution during his GSoC proeject.

It can be watched at:

LV2 branch: https://github.com/mixxxdj/mixxx/pull/316

EQ Rack: https://github.com/mixxxdj/mixxx/pull/330

Essence:

It fetures two types of controls:

Knob controls, for all parameters that are intended to be controlled by the superknob
Button controls, for all step parameters. It features a normal button Widget + a flyout menu with the enumeration values.

Discussion

TODO:

Thoughts:

LV2 and VST uses c float type to express all kinds values. Mixxx uses double types for the same. Conclusion: there is no need to convert double to QVariant and back. Double parameters are just fine.

We need to have a way to connect to Buttons and Rotaries on the DJ controller. The effect needs to control from where the value should be controlled.

All effect parameters that are usable to tweak while the effect is active should be placed on a Rotary control since not all controllers are featuring buttons for effects.

We need to extend enum ControlHint() to express more complex Scales.

Mixxx This is the Mixxx Wiki - Wiki Home | Website | Manual | News