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https://github.com/bradhowes/sf2libau

AUv3 MIDI instrument with sound font (SF2) rendering
https://github.com/bradhowes/sf2libau

audio-processing auv3 coreaudio ios macos sf2 soundfont

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AUv3 MIDI instrument with sound font (SF2) rendering

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# SF2LibAU - AUv3 MIDI instrument with sound font (SF2) rendering [BETA]



The code defines an AUAudioUnit MIDI component in Swift that uses the

[SF2Lib](https://github.com/bradhowes/SF2Lib) engine for rendering audio samples.



Currently, the AUv3 component:



* responds to MIDI messages and can render audio

* supports loading of SF2 files via custom sysex MIDI command

* supports selecting of a preset by bank/program as well as index position



The unit tests contain examples showing all of the above.



NOTE: requires Swift 5.9 for it's Swift/C++ interoperability facility.



# Parameter Control



An SF2 file contains a collection of instruments and presets each of which contains a set of values for the SF2 

synthesizer parameters (generators) and modulator mappings; those for instruments are absolute values, while the

preset values are always relative, adding to an instrument's value. Many of these parameters can be modified in

real-time by two means:



* AUv3 parameter changes communicated via the 

  [AUParameterTree](https://developer.apple.com/documentation/audiotoolbox/auparametertree) instance provided by

  the AUv3 instrument.



* MIDI control messages using "NRPN" MIDI control. From the SF2 spec:



> NRPN stands for Non Registered Parameter Number. The MIDI specification has defined this series of continuous 

> controllers to permit General MIDI compatible synthesizers to take advantage of their proprietary hardware by using 

> these messages to control the non-General MIDI compatible aspects of their hardware. The SoundFont 2.01 specification 

> uses these messages to allow arbitrary real-time control over all SoundFont synthesis parameters.



Note that some MIDI control messages will by default also effect a parameter change. For instance, MIDI pitch bend

messages affect the pitch of the note being played, and MIDI controllers 64 (sustain pedal), 66 (soft pedal), and 67

(sostenuto pedal) affect the envelope behavior of a playing note.



## AUParameterTree



The AUParameterTree for the SF2 engine contains entries for all of the implemented generators. See the SF spec for 

descriptions of these generators and their valid value ranges.



Address | Name |

---: | --- |

0 | startAddrsOffset

1 | endAddrsOffset

2 | startloopAddrsOffset

3 | endloopAddrsOffset

4 | startAddrsCoarseOffset

5 | modLfoToPitch

6 | vibLfoToPitch

7 | modEnvToPitch

8 | initialFilterFc

9 | initialFilterQ

10 | modLfoToFilterFc

11 | modEnvToFilterFc

12 | endAddrsCoarseOffset

13 | modLfoToVolume

15 | chorusEffectsSend

16 | reverbEffectsSend

17 | pan

21 | delayModLFO

22 | freqModLFO

23 | delayVibLFO

24 | freqVibLFO

25 | delayModEnv

26 | attackModEnv

27 | holdModEnv

28 | decayModEnv

29 | sustainModEnv

30 | releaseModEnv

31 | keynumToModEnvHold

32 | keynumToModEnvDecay

33 | delayVolEnv

34 | attackVolEnv

35 | holdVolEnv

36 | decayVolEnv

37 | sustainVolEnv

38 | releaseVolEnv

39 | keynumToVolEnvHold

40 | keynumToVolEnvDecay

43 | keyRange

44 | velRange

45 | startloopAddrsCoarseOffset

46 | keynum

47 | velocity

48 | initialAttenuation

50 | endloopAddrsCoarseOffset

51 | coarseTune

52 | fineTune

54 | sampleModes

56 | scaleTuning

57 | exclusiveClass

58 | overridingRootKey



> NOTE: any address not listed above will not be found in the AUParameterTree due to gaps in the SF spec.



All values for the elements in the AUParameterTree are floating-point values which will be converted into integer values

that conform to the spec. For boolean (true/false )settings, values < 0.5 will be treated as `false` and values >= 0.5 

will be `true`.



There are additional parameters definitions for MIDI control state:



Address | Name | Description

---: | ------------------------- | --------------------------------------------------------------------

1000 | portamentoModeEnabled     | Portamento mode (aka glide)

1001 | portamentoRate            | How must time to transition for each step

1002 | oneVoicePerKeyModeEnabled | When enabled, playing same key will cancel previous voice

1003 | polyphonicModeEnabled     | When enabled, supports playing multiple notes at same time

1004 | activeVoiceCount          | Reports the number of active voices (read-only)

1005 | retriggerModeEnabled      | When enabled, playing same voice restarts the envelope of the voice