Recording sound from mic during Oculus LipSync.

I have found the solution working on Rift and Quest:

// I have created my own class OculusLipSyncMicInput, copied into it source code from
// Oculus' OVRLipSyncMicInput.cs, and made several modifications:
public class OculusLipSyncMicInput : MonoBehaviour
{
...
    private int _micNdx = 0;
    private AudioClip _recordedClip;
    private AudioClip _croppedClip;
    private bool _isRecordingSpeech = false;
...
    void Start()
    {
      audioSource.loop = true;
      audioSource.mute = false;

      bool micSelected = false;
      _micNdx = 0;
      if (Microphone.devices.Length > 1)
      {
        for (int i = 0; !micSelected && (i < Microphone.devices.Length); i++)
        {
          if (Microphone.devices[i].ToString().Contains("Rift"))
          {
            _micNdx = i;
            micSelected = true;
          }
        }

        for (int i = 0; !micSelected && (i < Microphone.devices.Length); i++)
        {
          if (Microphone.devices[i].ToString().Contains("Oculus"))
          {
            _micNdx = i;
            micSelected = true;
          }
        }
      }
      InitializeMicrophone();
    }
...
    private void InitializeMicrophone()
    {
      if (initialized)
      {
        return;
      }
      if (Microphone.devices.Length == 0)
      {
        return;
      }

//      selectedDevice = Microphone.devices[0].ToString(); // Oculus' code
      selectedDevice = Microphone.devices[_micNdx].ToString(); // My code
      micSelected = true;
      GetMicCaps();
      initialized = true;
    }
...
//    public void StartMicrophone() // Oculus' code
    public void StartMicrophone(int soundLenSec = 1) // My code
    {
      if (micSelected == false) return;

      //Starts recording
//      audioSource.clip = Microphone.Start(selectedDevice, true, 1, micFrequency); // Oculus' code
      audioSource.clip = Microphone.Start(selectedDevice, true, soundLenSec, micFrequency); // My code

      Stopwatch timer = Stopwatch.StartNew();

      // Wait until the recording has started
      while (!(Microphone.GetPosition(selectedDevice) > 0) && timer.Elapsed.TotalMilliseconds < 1000)
      {
        Thread.Sleep(50);
      }

      if (Microphone.GetPosition(selectedDevice) <= 0)
      {
        throw new Exception("Timeout initializing microphone " + selectedDevice);
      }
      // Play the audio source
      audioSource.Play();
    }
...
// And I added several methods at the end
    public void StartMicrophoneRecord (int soundLenSec)
    {
      StopMicrophone();
      StartMicrophone(soundLenSec);
      _isRecordingSpeech = true;
    }

    public void EndMicrophoneRecord ()
    {
      int recordedSamples = Microphone.GetPosition(null);
      _recordedClip = (audioSource == null) ? null : audioSource.clip;
      StopMicrophone();

      if (_isRecordingSpeech)
      {
        if ((audioSource == null) || (audioSource.clip == null))
        {
          _recordedClip = null;
        }
        else
        {
          float[] croppedData = new float[recordedSamples * _recordedClip.channels];
          _recordedClip.GetData(croppedData, 0);
          if (_croppedClip != null)
          {
            _croppedClip.UnloadAudioData();
            Destroy(_croppedClip);
          }
          _croppedClip = AudioClip.Create(_recordedClip.name, recordedSamples, _recordedClip.channels, _recordedClip.frequency, false);
          _croppedClip.SetData(croppedData, 0);
        }
        _isRecordingSpeech = false;
      }

      StartMicrophone(1);
    }

    public AudioClip GetMicrophoneRecord ()
    {
      return _croppedClip;
    }

    public void Mute ()
    {
      micInputVolume = 0;
    }

    public void Unmute ()
    {
      micInputVolume = 100;
    }
}