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