My project has uses an AVAudioEngine with a very simple setup: A Speech recognizer running on a tap on the engine's input with separate AVAudioPlayerNodes handling playback.
try session.setCategory(.playAndRecord, mode: .default, options: [])
try session.setActive(true, options: .notifyOthersOnDeactivation)
try session.setAllowHapticsAndSystemSoundsDuringRecording(true)
filePlayerNode ---> engine.mainMixerNode
bufferPlayerNode --> engine.mainMixerNode
engine.mainMixerNode --> engine.outputNode
//bufferPlayer.scheduleBuffer() is called on its own queue
The input works fine since the buffers can be collected into a file and plays back correctly, and also because the recognizer works fine; but when I try to play the live audio by sending the buffer to the bufferPlayer on this or another device, the buffer audio plays at a very low volume, sometimes with severe distortions. If I lower the sample rate via AVAudioConverter, the distortions get worse.
I've tried experimenting with the AVAudioSession category options, having separate AVAudioEngines, and much, much more, yet I still haven't figured this out. It's gotten to the point where I've fixed almost all the arcane and minor issues in my audio system, yet I still can't play back my voice properly.
The ability to both play and record simultaneously is a basic feature of phones--when on speaker mode, a phone doesn't need to behave like a walkie-talkie. In my mind, it's inconceivable that the relatively new AVAudioEngine doesn't have a implementation for this, since the main issue (feedback loops) can be dealt with via a simple primitive circuit. Live video chat apps like FaceTime wouldn't be possible without this, yet to my surprise I found no answers online (what I did find were articles explaining how to write a file while playback is occurring).
Is there truly no way to do this on AVAudioEngine? Am I missing something fundamental? Any pointers would be greatly appreciated