noise_meter

Noise Meter

A noise meter plugin 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 in XCode:

• 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 example app for how to use the plugin. This app also illustrated how to obtain permission to access the microphone.

Noise sampling happens by listening to the noise stream, like this:

NoiseMeter().noise.listen(
  (NoiseReading noiseReading) {
    print('Noise: ${noiseReading.meanDecibel} dB');
    print('Max amp: ${noiseReading.maxDecibel} dB');
  },
  onError: (Object error) {
    print(error);
  },
  cancelOnError: true,
);

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)