AUSampler stuck notes

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Created Dec ’20

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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).

Answered by cjed in 654903022

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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Answer 1

cjed OP

Dec ’20

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

0

Answer 2

cjed OP

Dec ’20

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.

0

Answer 3

cjed OP

Jan ’21

Accepted Answer

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

0