elm-soundfont

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Elm 0.16 MIDI player using sound fonts and Web-Audio (deprecated)

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elm-soundfont
=============

This project explores the possibilities of playing MIDI directly in the browser within an Elm (0.16) application.  It uses three putative Elm libraries:

*   Elm-webmidi.  This library is a simple wrapper round [Web-MIDI](http://www.w3.org/TR/webmidi/) and provides signals of connection/disconnection of MIDI input devices and also of MIDI notes (for example whenever a key is pressed on a MIDI keyboard).  I doubt if I will ever now publish this as a 'blessed' Elm Community Package because of the moratorium on Native libraries and the lack of clarity about what the future might hold. Unfortunately, this code must be reproduced from [newlandsvalley/elm-webmidi](https://github.com/newlandsvalley/elm-webmidi) because linking seems difficult in any other manner.

*   Elm-comidi.  This is a parser for MIDI file images which uses the elm-combine parser combinator library and is now 'sanctified' as a community package.

*   SoundFont.  This library is a simple native code wrapper around the essential features of the [soundfont-player](https://github.com/danigb/soundfont-player) from danigb. At the moment it chooses just one sound font - an acoustic grand piano - taken from Benjamin Gleitzman's package of [pre-rendered sound fonts](https://github.com/gleitz/midi-js-soundfonts). It provides a signal of Audio Buffers for each possible MIDI note and uses [Web-Audio](https://webaudio.github.io/web-audio-api/) to play the sounds. Much of this would eventually probably be better written in pure Elm but the reliance on Web-Audio by means of some sort of native interface remains.

At the moment, the sample file players handle only Type-0 MIDI files but the intention is eventually to handle Type-1 and Type-2 as well.

Elm 0.17
--------

Of the three libraries mentioned above, _elm-comidi_ has been ported to 0.17 and _elm-webmidi_ has been deprecated.  This project has now been moved to [elm-soundfont-ports](https://github.com/newlandsvalley/elm-soundfont-ports). The native _soundfont_ library has been re-written and uses elm ports.

Examples
--------

#### MIDI Keyboard

[Piano](https://github.com/newlandsvalley/elm-soundfont/tree/master/src/examples/piano) is a bare-bones application that plays notes that are detected from an attached MIDI keyboard.  It first loads the acoustic grand piano soundfont into a Dictionary of AudioBuffers (one for each note).  It then detects keyboard presses and plays the corresponding note using the Web-Audio API.  To build, use:

elm-make src/examples/piano/Main.elm --output=Main.html

#### MIDI File

[Simpleplayer](https://github.com/newlandsvalley/elm-soundfont/tree/master/src/examples/simpleplayer) is a simple MIDI file player (it plays a Swedish tune called 'Lillasystern').  It first loads the acoustic grand piano soundfont as before, loads and parses the MIDI file and converts this into a performance simply by accumulating the elapsed times of each 'NoteOn' event. It then converts each of these to a playable 'sound bite' attached to the appropriate soundfont and plays them as a single uninterruptable Task. The player can be used with any type of MIDI file, but for multi-track input only the first melody track will be played. To build use:

elm-make src/examples/simpleplayer/Main.elm --output=Main.html

#### MIDI Audio Controller

[Type0player](https://github.com/newlandsvalley/elm-soundfont/tree/master/src/examples/type0player) is another MIDI file player. But here, the playback is controlled by means of start/pause/continue buttons in a half-finished CSS-styled player. The file must conform to MIDI type-0 (i.e. single track). To build use:

elm-make src/examples/type0player/Main.elm --output=Main.html

Issues
------

The sample tune has a tempo of 120 bpm which is what the simple player delivers naturally. However, the audio controller player uses myriad small tasks each of which induces a small delay in playing the sound. In response, I have reduced the time delay between successive notes by multiplying by a factor (named elmPlayerOverhead) which is currently set to 0.923.  This then delivers the tempo of 120 bpm.

I was hamstrung under Elm 0.15 by [this issue](https://github.com/elm-lang/core/issues/240) whenever I attempted to use Native Task.asyncFunction when the function implementation itself uses asynchronous javascript methods.  In consequence, I modeled all asynchronous interfaces as signals rather than tasks. This bug is now fixed in Elm 0.16, which in turn allows me to initialise connections to MIDI devices as a Task.  However I have (so far) retained the use of signals for loading soundfonts.

I think it is not yet possible to build a player for Type-1 files (multiple tracks played simultaneously) with Elm in its current state.  This is because we need concurrency primitives which can be used with the Task library.  See [this discussion](https://groups.google.com/forum/#!topic/elm-discuss/NDAYIAML438).

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