You may try to obtain the sample rate by : let input = avAudioEngine.inputNode let sampleRate = input.inputFormat(forBus: 0).sampleRate // the default sample rate from mic is 48000 let channelCount = input.inputFormat(forBus: 0).channelCount // 1 then you can set your av audio format as following: let avAudioFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: sampleRate, channels: channelCount, interleaved: false)