BassMidiAudioUnit

Background

Apple's AVAudioUnitSampler doesn't support Soundfonts spec 2.01. This is a pity regarding the huge gain of quality brought by the support of "modulators" (more on this topic on sound designer Christian Collins' blog).

That's why at Newzik, we decided that instead we should use the great BASSMIDI player built by Un4seen which is one of the few library on the market to support SoundFont version 2.01.

Overview

The goal of this project is to embed the BASSMIDI library into an AUv3 Audio Unit, so it acts as a Sampler node. This way, it makes it possible to insert it into a graph of audio nodes handled by the iOS Audio Engine.

Basic usage

The BassMidiAudioUnit is enclosed in a xcframework that you should import at the top of your file:

import BassMidiAudioUnitFramework

1. Set the sampling rate of the BASSMIDI library

BassMidiAudioUnit.setup(sampleRate: 44100)

2. Instantiate a BASSMIDI Audio Unit

BassMidiAudioUnit.instantiate(soundFontPath: soundFontPath) { result in
    guard case .success(let container) = result else { return }
}

This will return a container object of type :

public struct BassMidiAudioUnitContainer {
    public let avAudioUnit: AVAudioUnit
    public let audioUnit: BassMidiAudioUnit
}

This way you can attach and connect the AVAudioUnit object to the AVAudioEngine and set it as the destinationAudioUnit of a AVMusicTrack:

engine.attach(audioUnit)
let outputHWFormat = engine.outputNode.outputFormat(forBus: 0)
engine.connect(audioUnit, to: engine.mainMixerNode, format: outputHWFormat)
track.destinationAudioUnit = audioUnit

Additional options

Several additional options can be performed on the audio unit including: transposition, mute and force a program change.

Transposition

You can apply a MIDI transposition to the BassMidiAudioUnit object by setting a semitone offset value:

bassMidiAudioUnit.transposition = -2 // - 2 semitones

Muting

It is also possible to mute the audio output of the BassMidiAudioUnit:

bassMidiAudioUnit.isMuted = true

Force Program Change

We also can force a MIDI program change event, in order to select a specific MIDI instrument among the GM Program instrument sound list. (In this case, all subsequent Program Change Events contained in the MIDI sequence will be ignored)

bassMidiAudioUnit.instrument = 22 // Accordion

About Newzik App 🎼

The Newzik app is a wonderful iOS app built for musicians, to create and organize your digital music library. Go check our website if you want to known more about us.

License

BassMidiAudioUnit is distributed under the MIT license. See LICENSE for details. Please note that this license does not cover the BASS/BASSMIDI libraries, which need to be licensed separately.