noise_meter 4.0.1

A Flutter plugin for collecting noise from the phone's microphone.

Noise Meter

A noise meter package for iOS and Android.

Install

Add noise_meter as a dependency in pubspec.yaml. For help on adding as a dependency, view the documentation.

On Android you need to add a permission to AndroidManifest.xml:

<uses-permission android:name="android.permission.RECORD_AUDIO" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

On iOS enable the following:

• Capabilities > Background Modes > Audio, AirPlay and Picture in Picture
• In the Runner Xcode project edit the Info.plist file. Add an entry for 'Privacy - Microphone Usage Description'
• Edit the Podfile to include the permission for the microphone:

post_install do |installer|
  installer.pods_project.targets.each do |target|
    flutter_additional_ios_build_settings(target)
    target.build_configurations.each do |config|
      # for more infomation: https://github.com/BaseflowIT/flutter-permission-handler/blob/master/permission_handler/ios/Classes/PermissionHandlerEnums.h
      config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] ||= [
        '$(inherited)',
        'PERMISSION_MICROPHONE=1',]
    end
  end
end

Usage

See the full example app for how to use the plugin.

Initialization

The example app uses these variables:

  bool _isRecording = false;
  NoiseReading? _latestReading;
  StreamSubscription<NoiseReading>? _noiseSubscription;
  NoiseMeter? _noiseMeter;

Start listening

You listen to noise readings via the noise stream on the NoiseMeter instance.

  void start() {
    try {
      _noiseSubscription = _noiseMeter?.noise.listen(onData);
    } catch (err) {
      print(err);
    }
  }

On data

When data is streamed, it will be send to the onData method, specified when the subscription was created. The incoming data points are of type NoiseReading which holds the mean and maximum decibel reading.

  void onData(NoiseReading noiseReading) {
    this.setState(() {
      _latestReading = noiseReading;
      if (!this._isRecording) this._isRecording = true;
    });
  }

On errors

Platform errors may occur when recording is interrupted. You must decide what happens if such an error occurs. The [onError] callback must be of type void Function(Object error) or void Function(Object error, StackTrace trace).

  void onError(Object error) {
    print(error);
    _isRecording = false;
  }

Stop listening

To stop listening, the cancel method is called on the subscription object.

  void stop() {
    try {
      _noiseSubscription?.cancel();
      this.setState(() {
        this._isRecording = false;
      });
    } catch (err) {
      print(err);
    }
  }

Technical documentation

Sample rate

The sample rate for both Android and iOS implementations are 44,100.

Microphone data

The native implementations record PCM data using the microphone of the device, and uses an audio buffer array to store the incoming data. When the buffer is filled, the contents are emitted to the Flutter side. The incoming floating point values are between -1 and 1 which is the PCM values divided by the max amplitude value which is 2^15.

Conversion to Decibel

Computing the decibel of a PCM value is done as follows:

db = 20 * log10(2**15 * pcmValue)