Question SpeechSynthesizer.SetOutputToAudioStream audio format problem

System.Speech.AudioFormat.SpeechAudioFormatInfo synthFormat =
                        new System.Speech.AudioFormat.SpeechAudioFormatInfo(System.Speech.AudioFormat.EncodingFormat.Pcm,
                            8000, 16, 1, 16000, 2, null);

SpeechSynthesizer synthesizer = new SpeechSynthesizer();
waveStream = new MemoryStream();

PromptBuilder pbuilder = new PromptBuilder();
PromptStyle pStyle = new PromptStyle();

pStyle.Emphasis = PromptEmphasis.None;
pStyle.Rate = PromptRate.Fast;
pStyle.Volume = PromptVolume.ExtraLoud;

pbuilder.StartStyle(pStyle);
pbuilder.StartParagraph();
pbuilder.StartVoice(VoiceGender.Male, VoiceAge.Teen, 2);
pbuilder.StartSentence();
pbuilder.AppendText("This is some text.");
pbuilder.EndSentence();
pbuilder.EndVoice();
pbuilder.EndParagraph();
pbuilder.EndStyle();

synthesizer.SetOutputToAudioStream(waveStream, synthFormat);
synthesizer.Speak(pbuilder);
synthesizer.SetOutputToNull();

pbuilder.StartStyle(pStyle);
pbuilder.StartParagraph();
pbuilder.StartVoice(VoiceGender.Male, VoiceAge.Teen, 2);
pbuilder.StartSentence();
pbuilder.AppendText("Checking current weather.");
pbuilder.EndSentence();
pbuilder.EndVoice();
pbuilder.EndParagraph();
pbuilder.EndStyle();
ss.SpeakAsync(pbuilder);

ss.SpeakAsync("Checking current weather");