Control All Your Programs With MIDI Controllers Tobi Wulff KiwiPyCon 2014 

MIDI Controllers 

The Good: Standardised Protocol No worries about OS drivers Lots of connections and daisy chaining Reusability Libraries for Arduino, and more Cheap MIDI­to­USB adapters 

MIDI Controllers Mixer boards Pads Keyboards (Piano) Even drum kits 

Lighting Console www.alg­uk.com 

Keyboards www.openmusiclabs.com 

Keyboards www.flickr.com (Stephen Drake) 

Drums musicradar.com 

Drums performing­musician.com 

MIDI Controller Components Sliders, Buttons, Potis, Rotary Encoders, Keyboard, Trackpads, ... www.bauerindustries.com 

The Protocol and Theory Controllers generate notes and controlling messages Software can generate or process (play) messages Synthesisers can play MIDI messages => Keyboards are controller + synthesisers 

MIDI Messages www.sebkhachott.net 

MIDI Messages Can be sent on specific channels: 0(all) ­ 15 Data is in the range of 0­127 On/off usually done with ≤ 63 and ≥ 64 Control Change [Control, Value] Program Change Note On/Off [Note, Speed] Pitch Bend SysEx Panic! Note Off for all notes 

MIDI Messages midi­protocol.wikispaces.com 

Quick Excursion Linux Audio: basic layer (ALSA) Real­time and routing with Jack (jackd) Mididings can connect to both of those 

Audio Connections 

MIDI Connections 

The Target: Darktable 

The Target: Darktable Alternative: API 

Introducing: mididings Can receive, process and send MIDI messages das.nasophon.de 

A small Mididings Example f r o m m i d i d i n g s i m p o r t r u n , P r o c e s s , N O T E O N d e f i n v e r t ( e v e n t ) : i f e v e n t . c h a n n e l = = 1 a n d e v e n t . t y p e = = N O T E O N : e v e n t . v e l o c i t y = 1 2 7 - e v e n t . v e l o c i t y r e t u r n e v e n t r u n ( P r o c e s s ( i n v e r t ) ) 

Domain Specific Languages "A domain­specific language (DSL) is a computer language specialized to a particular application domain." 

Mididings as a DSL p i a n o = O u t p u t ( ' s a m p l e r ' , 1 , 1 ) # p o r t , c h , p r g s t r i n g s = O u t p u t ( ' s y n t h ' , 2 ) # p o r t , c h , p r g C h a n n e l F i l t e r ( 1 ) > > K e y S p l i t ( ' c 3 ' , p i a n o , s t r i n g s ) 

Mididings as a DSL F i l t e r ( C T R L ) > > C h a n n e l ( 2 ) F i l t e r ( N O T E O N ) > > T r a n s p o s e ( - 1 2 ) > > o r c h e s t r a / / b e l l s { C T R L : C h a n n e l ( 2 ) , N O T E O N : T r a n s p o s e ( - 1 2 ) > > [ o r c h e s t r a , b e l l s ] } 

Mididings as a DSL ( ( C h a n n e l F i l t e r ( 1 ) & ( C t r l F i l t e r ( 2 3 ) | C t r l F i l t e r ( 4 2 ) ) ) & ~ C t r l V a l u e F i l t e r ( l o w e r = 5 0 , u p p e r = 1 0 0 ) ) > > C h a n n e l ( 2 ) 

Mididings as a DSL ( # o n l y u s e c h a n n e l 1 ( C h a n n e l F i l t e r ( 1 ) & # C C # 2 3 o r 4 2 ( C t r l F i l t e r ( 2 3 ) | C t r l F i l t e r ( 4 2 ) ) ) & # s l i d e r n o t b e t w . 5 0 a n d 1 0 0 ~ C t r l V a l u e F i l t e r ( l o w e r = 5 0 , u p p e r = 1 0 0 ) ) # s e n d T H O S E m e s s a g e s t o c h . 2 > > C h a n n e l ( 2 ) 

das.nasophon.de 

CTRL specific functions C t r l M a p ( ) # c h a n g e s C C # C t r l R a n g e ( ) # c h a n g e s v a l u e C t r l C u r v e ( ) # a p p l y a c u r v e t o v a l u e s Should use those more 

Ok, back to controlling GUIs 1. Collect incoming MIDI messages (filtered) 2. Grab collected events and process 3. Turn event into key press (or something else) 4. Send off key press 

Collect Main process acting as a producer adding items to the event queue. Overwrite if same event happens again. r u n ( P r o c e s s ( c o l l e c t ) ) d e f c o l l e c t ( s e l f , m i d i ) : w i t h s e l f . _ e v e n t s _ l o c k : s e l f . _ c o l l e c t ( m i d i ) 

Grab Second thread acting as a consumer taking items from the event queue. i m p o r t t h r e a d i n g w i t h s e l f . _ l o c k : s e l f . _ e v e n t s . i t e m s ( ) 

Key Press Map MIDI message to shortcut action object: M A P = { ( 0 , C T R L , 1 1 ) : ( ' W i n d o w ' , S h o r t c u t A c t i o n ( N O _ M O D , ' o ' ) ) , . . . } c l a s s S h o r t c u t A c t i o n ( o b j e c t ) : d e f _ _ i n i t _ _ ( s e l f , m o d i f i e r s , k e y , f u n c = N o n e ) : . . . d e f r u n ( s e l f , e x e c u t o r , v a l u e ) : . . . c l a s s S h o r t c u t A c t i o n S e q u e n c e ( o b j e c t ) : . . . 

Send Will only go to foreground window (unless special global shortcut). f r o m s u b p r o c e s s i m p o r t P o p e n , P I P E k e y _ s e q u e n c e = [ ' k e y d o w n C o n t r o l _ L ' , ' k e y o ' , ' k e y u p C o n t r o l _ L ' , ' s t r 1 . 3 3 ' ] P o p e n ( [ ' x t e ' ] , s t d i n = P I P E ) . c o m m u n i c a t e ( i n p u t = k e y _ s e q u e n c e ) 

The Future OSC will probably replace MIDI: mididings ­> S e n d O S C Extend to send to other OS (not just using xte) More flexibility for other programs (GIMP, ...) Mouse etc macros Feedback (MIDI from PC to controller) 

References For more theory: www.midi.org This program: github.com/tobiw/midi2gui Mididings: (part of most Linux package managers) das.nasophon.de Xte: xautomation.sf.net 

Contact Me T w i t t e r : t o b i a s w u l f f G i t h u b a n d I R C : t o b i w J a b b e r a n d E m a i l : t o b i ( a ) s w u l f f . d e