import 'package:permission_handler/permission_handler.dart';
[...]
/// If you are running on Android, MacOS or iOS, ask the permission to use the microphone:
if (defaultTargetPlatform == TargetPlatform.android ||
    defaultTargetPlatform == TargetPlatform.iOS ||
    defaultTargetPlatform == TargetPlatform.macOS) {
    Permission.microphone.request().isGranted.then((value) async {
    if (!value) {
        await [Permission.microphone].request();
    }
});

/// Initialize the capture device and start it:
try {
    Recorder.instance.init();
    Recorder.instance.start();
} on Exception catch (e) {
    debugPrint('init() error: $e\n');
}
/// On Web platform it is better to initialize and wait the user to give
/// mic permission. Then use `start()` when it's needed.

//Start recording:
Recorder.instance.startRecording(completeFilePath: 'audioCompleteFilenameWithPath.wav`);

/// Stop recording:
Recorder.instance.stopRecording();

Recorder.instance.setSilenceDetection(
    enable: true,
    onSilenceChanged: (isSilent, decibel) {
        /// Here you can check if silence is changed.
        /// Or you can do the same thing with the Stream
        /// [Recorder.instance.silenceChangedEvents]
    },
);
/// the silence threshold in dB. A volume under this value is considered to be silence.
Recorder.instance.setSilenceThresholdDb(-27);
/// the value in seconds of silence after which silence is considered as such.
Recorder.instance.setSilenceDuration(0.5);
/// Set seconds of audio to write before starting recording again after silence.
Recorder.instance.setSecondsOfAudioToWriteBefore(0.0);

/// Get the current volume in dB in the [-100, 0] range.
double volume = Recorder.instance.getVolumeDb();
/// Return a 256 float array containing wave data in the range [-1.0, 1.0] not clamped.
Float32List waveAudio = Recorder.instance.getWave();
/// Return a 256 float array containing FFT data in the range [-1.0, 1.0] not clamped.
Float32List fftAudio = Recorder.instance.getFft();

/// Listen to audio data stream. The data is received in Uint8List.
Recorder.instance.uint8ListStream.listen((data) {
    /// the [data] is of type `AudioDataContainer` and, whatever format is passed to
    /// the `init()` method, it is available with [data.rawData] which is of `Uint8List`
    /// type. This is useful if we want to write into a file.
    /// It is possible to convert audio data to the desired format using one of the
    /// `data.to[*]List` methods. Be aware that the conversion is compute expensive and
    /// should be avoided if possible initializing the recorder with the format
    /// desired.
});

/// Start streaming:
Recorder.instance.startStreamingData();
/// Stop streaming:
Recorder.instance.stopStreamingData();