How to improve voice quality in Photon Voice?

The following code does establish Photon Voice networking but the quality of voice is not good. Plus there is a lot of noise. How do I make sure that there is minimal noise? Furthermore how do I pause and unpause sending of voice to the other users?

 using UnityEngine;
 using System.Collections;
 using Photon;
 public class NetworkManager : Photon.PunBehaviour
 {
     private GameObject studymaterial;
     void Start()
     {
         PhotonNetwork.ConnectUsingSettings("0.1");
         PhotonNetwork.automaticallySyncScene = true;
         PhotonVoiceNetwork.Connect();
         PhotonNetwork.logLevel = PhotonLogLevel.Full;
         studymaterial = null;
     }
 
     void OnGUI()
     {
         GUILayout.Label(PhotonNetwork.connectionStateDetailed.ToString());
     }
     
     public override void OnJoinedLobby()
     {
         RoomOptions roomOptions = new RoomOptions() { isVisible = true, maxPlayers = 18 };
         PhotonNetwork.JoinOrCreateRoom("Class", roomOptions, TypedLobby.Default);
     }
     public override void OnJoinedRoom()
     {
         PhotonNetwork.Instantiate("User", new Vector3(0, 1, 0), Quaternion.identity, 0);
        // studymaterial = PhotonNetwork.Instantiate("Heart3D", new Vector3(2, 1, 0), Quaternion.identity, 0);
 
     }
 
 }