Example of how to implement audio recorder in your Xamarin.Forms applications. - http://julianocustodio.com/gravar-audio

MainPage.xaml.cs

using System;
using System.ComponentModel;
using Plugin.AudioRecorder;
using Xamarin.Forms;

namespace AudioDemo
{

    [DesignTimeVisible(true)]
    public partial class MainPage : ContentPage
    {
        AudioRecorderService gravador;
        AudioPlayer reprodutor;

        public MainPage()
        {
            InitializeComponent();

            gravador = new AudioRecorderService
            {
                StopRecordingAfterTimeout = true,
                TotalAudioTimeout = TimeSpan.FromSeconds(15),
                AudioSilenceTimeout = TimeSpan.FromSeconds(2)
            };

            reprodutor = new AudioPlayer();
            reprodutor.FinishedPlaying += Finaliza_Reproducao;
        }

        public async void Gravar_Clicked(object sender, EventArgs e)
        {
        }

        public async void Reproduzir_Clicked(object sender, EventArgs e)
        {
        }


        public void Finaliza_Reproducao(object sender, EventArgs e)
        {
        }
    }
}