AUSampler stuck notes

Question

Hi,

I'm developing an AUSampler based application for iOS12.4x.
It manages incoming MIDI messages through the MIDIReadProc handler. Initially I sent notifications from this handler to have it respond faster and allow uncoupling with the AU rendering thread.
However I noticed stuck notes (as if some note off messages werent't handled) when playing many note repeatedly at the same time.
I then called MusicDeviceMIDIEvent directly from MIDIReadProc handler, however it didn't fix the problem.
It seems the AU Sampler cannot manage such load ?

Is there a new AUv3 sampler unit available that could help ?
I'm on High Sierra so I can't develop for iOS 13+.

I both manage noteoff (0x8) and 0 velocity note on (0x9) messages to stop playing (calling MusicDeviceMIDIEvent with 0 velocity value).

933

Posted by

cjed

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Answer 1

After looking into audioKit source code and finding articles about managing MIDIPacket indeed they contain a tuple data. We have to check its total size and then iterating over the pointer to get messages (status byte followed by one or two value bytes). It now works

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cjed

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Answer 2

Using new AVAudioUnitSampler (and AVAudioEngine/AVAudioSession instead AUGraph) didn't helped.

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cjed

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Answer 3

Using AudioKit 4.8 and Wrapper (AKMidiSampler/AKAppleSampler) for Apple's AVAudioUnitSampler fixed the problem, so the problem may come from the way I manage midi messages (however it is similar as how AudioKit does).
The code I'm using :

Code Block err = MIDIInputPortCreateWithBlock(client, portName, &port, onMIDIMessageReceived)

And handler defined as :

Code Block func onMIDIMessageReceived(message: UnsafePointer<MIDIPacketList>, srcConnRefCon: UnsafeMutableRawPointer?) {
        let packetList: MIDIPacketList = message.pointee
        let n = packetList.numPackets
        var packet = packetList.packet
        for _ in 0 ..< n {
          
            let mes: UInt8 = packet.data.0 & 0xF0
            let ch: UInt8 = packet.data.0 & 0x0F
            if mes == 0x90 && packet.data.2 != 0 {
               
                let noteNo = packet.data.1
                let velocity = packet.data.2
                DispatchQueue.main.async {
                    self.delegate?.noteOn(ch: ch, note: noteNo, vel: velocity)
                }
            } else if (mes == 0x80 || mes == 0x90) {
                
                let noteNo = packet.data.1
                let velocity = packet.data.2
                DispatchQueue.main.async {
                    self.delegate?.noteOff(ch: ch, note: noteNo, vel: velocity)
                }
            }
            let packetPtr = MIDIPacketNext(&packet)
            packet = packetPtr.pointee
        }
    }

I also tested without DispatchQueue.main.async (using it instead in the delegate when calling the sampler methods), same problem.

Posted by

cjed

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Answer 4

After looking into audioKit source code and finding articles about managing MIDIPacket indeed they contain a tuple data. We have to check its total size and then iterating over the pointer to get messages (status byte followed by one or two value bytes). It now works

Posted by

cjed

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AUSampler stuck notes

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