xamarin iOS：如何在录制时显示语音的音频幅度

Question

On Android, I have found to show the amplitude of the recording I can use getMaxAmplitude at a regular basis. Does iOS have the same function? I want to show the input voice volume meter while recording from the microphone.

Answer 1

Assuming you are using AVAudioRecorder you can enable metering and read the average and peak volumes (in decibels) for each audio channel.

Sample Microphone 10 times a second:

# AVAudioSettings setup ...
~~~
avAudioRecorder = AVAudioRecorder.Create(this.audioFilePath, new AudioSettings(settings), out error);
avAudioRecorder.MeteringEnabled = true;

var peakPower = 0.0;
var averagePower = 0.0;
// Note: No await, run the following Task synchronously!
Task.Run(async() => // Personally I would create my own Thread, but this works for a quick example
{
    while (true) // Do not create object/release objects or subtasks in this loop, it will cause poor performance due to GC.
    {
        if (!avAudioRecorder.Recording)
            return;
        avAudioRecorder.UpdateMeters();
        peakPower = avAudioRecorder.PeakPower(0);
        averagePower = avAudioRecorder.AveragePower(0);
        Console.WriteLine($"{averagePower}:{peakPower}");
        Thread.Sleep(100);
    }
});

Output:

2017-01-14 19:26:16.271 Sound[33399:19078946] -52.9222717285156:-48.1419296264648
2017-01-14 19:26:17.271 Sound[33399:19078946] -53.7662239074707:-45.7719497680664
2017-01-14 19:26:18.274 Sound[33399:19078946] -49.105827331543:-43.4426803588867
2017-01-14 19:26:19.275 Sound[33399:19078946] -9.97611618041992:4.59128427505493
2017-01-14 19:26:20.276 Sound[33399:19078946] -37.2582626342773:5.28962087631226
2017-01-14 19:26:21.276 Sound[33399:19078946] -24.4357891082764:4.00279855728149
2017-01-14 19:26:22.277 Sound[33399:19078946] -11.7632217407227:4.34794473648071
2017-01-14 19:26:23.278 Sound[33399:19078946] -32.4504356384277:5.66976404190063
2017-01-14 19:26:24.279 Sound[33399:19078946] -18.5233268737793:0.0205818619579077
2017-01-14 19:26:25.280 Sound[33399:19078946] -28.790828704834:-5.83084678649902

Ref: https://developer.apple.com/reference/avfoundation/avaudiorecorder

in decibels, for the sound being recorded. A return value of 0 dB indicates full scale, or maximum power; a return value of -160 dB indicates minimum power (that is, near silence).

If the signal provided to the audio recorder exceeds ±full scale, then the return value may exceed 0 (that is, it may enter the positive range).