The AVAudioEngine is responsible for receiving the audio signals from the microphone. It provides our input for speech recognition.

ios-setup-audioengine.swift

let audioEngine = AVAudioEngine()
let audioSession = AVAudioSession.sharedInstance()
try audioSession.setCategory(.record, mode: .measurement, options: .duckOthers)
try audioSession.setActive(true, options: .notifyOthersOnDeactivation)

let inputNode = audioEngine.inputNode

inputNode.removeTap(onBus: 0)
        let recordingFormat = inputNode.outputFormat(forBus: 0)
        inputNode.installTap(onBus: 0, bufferSize: 1024, format: recordingFormat) { (buffer: AVAudioPCMBuffer, when: AVAudioTime) in
            self.recognitionRequest?.append(buffer)
        }
        
audioEngine.prepare()
try audioEngine.start()