AVAudioEngine downsample issue

Question

I\'m having an issue with downsampling audio taken from the microphone. I\'m using AVAudioEngine to take samples from the microphone with the following code:

Answer 1

An other way to do it , with AVAudioConverter in Swift 5

let engine = AVAudioEngine()


func setup() {

    let input = engine.inputNode
    let bus = 0
    let inputFormat = input.outputFormat(forBus: bus )
    guard let outputFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: 8000, channels: 1, interleaved: true), let converter = AVAudioConverter(from: inputFormat, to: outputFormat) else{
        return
    }

    input.installTap(onBus: bus, bufferSize: 1024, format: inputFormat) { (buffer, time) -> Void in
        var newBufferAvailable = true

        let inputCallback: AVAudioConverterInputBlock = { inNumPackets, outStatus in
            if newBufferAvailable {
                outStatus.pointee = .haveData
                newBufferAvailable = false
                return buffer
            } else {
                outStatus.pointee = .noDataNow
                return nil
            }
        }

        if let convertedBuffer = AVAudioPCMBuffer(pcmFormat: outputFormat, frameCapacity: AVAudioFrameCount(outputFormat.sampleRate) * buffer.frameLength / AVAudioFrameCount(buffer.format.sampleRate)){
            var error: NSError?
            let status = converter.convert(to: convertedBuffer, error: &error, withInputFrom: inputCallback)
            assert(status != .error)

            // 8kHz buffers
            print(convertedBuffer.format)
        }
    }
    do {
        try engine.start()
    } catch { print(error) }
}