How to change the sample rate of a real device in ios

Question

I'm developing a simple recording app using AVAudioSession , AVAudioRecorder . And I'm having trouble changing the sample rate of a ios real device.

An attempt was made to change the sample rate using the setPreferredSampleRate function, and this attempt was well applied in all simulators. In this case, I checked that the sample rate has changed by checking the sampleRate property of AVAudioSession .

However, it didn't work on a real device. As a result of checking the sampleRate property, only the value of 48000 was found in the real device. The devices I tested were iphone 8 and iphone 8+.

I googled and read a lot of stackoverflow articles, but it was hard to find an article that could be applied to my problem.

Then I found an article , I read that "The internal speaker on the iPhone 6S models only support a sample rate of 48kHz."

I wonder if there is no way to change the sample rate in a real device as long as the internal speaker is used.

If there is a way, I don't think it's just to use setPreferredSampleRate ... I'd appreciate it if you could tell me how to do it.

Below is the class I wrote to manage AVAudioSession. I changed the sample rate and checked the value using the method below.

class AudioSessionManager{

private let audioSession = AVAudioSession.sharedInstance()

func setAudioSession() {
    do {
        try audioSession.setCategory(.playAndRecord, options: .defaultToSpeaker)
        audioSession.requestRecordPermission{ accepted in
            if accepted {
                print("permission granted")
            }
        }
    } catch {
        print("audioSession error: \(error.localizedDescription)")
    }
}

func setSampleRate(_ sampleRate : Double) {
    do {
        try audioSession.setPreferredSampleRate(sampleRate)
    } catch {
        print("audioSession error: \(error.localizedDescription)")
    }
}

func getSampleRate() -> Double {
    return audioSession.sampleRate
}

}

Answer 1

You may possibly need to set automaticallyConfiguresApplicationAudioSession for the session to false before your settings are applied so that they are not overridden by the system.

Related question and answer: AVCaptureSession audio samples captured at different frequency than AVAudioSession's sample rate