Синтез речи в отдельном потоке

Imports System.Speech.Synthesis
 
Public Class Form1
 
    Dim phrase_syntesizer As New SpeechSynthesizer
    Dim phrase_to_speak As String
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Label1.Text = Format(TimeOfDay, "HH:mm:ss")
        Label1.Cursor = Cursors.Hand
        Timer1.Interval = 1000
        Timer1.Enabled = True
    End Sub
 
    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        Label1.Text = Format(TimeOfDay, "HH:mm:ss")
    End Sub
 
    Private Sub Label1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Label1.Click
        phrase_to_speak = Format(TimeOfDay, "HH:mm")
        phrase_syntesizer.Speak(phrase_to_speak)
    End Sub
End Class

  Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Dim th As New Threading.Thread(AddressOf XX) : th.Start("Проверка работы голоса за кадром.")
    End Sub
 
    Private Sub XX(ByVal strText As String)
        Dim objVoice, objHTML As Object
        objVoice = CreateObject("SPEECH.SpVoice")
        If strText <> "" Then
            objVoice.speak(strText)
        End If
    End Sub