如何利用direcx进行录音？(100分)

我使用了delphix2000中的TDXsound控件。代码如下，可是保存出来的文件不是正确wav文件，请高手赐教！

procedure TForm1.btn_RecordClick(Sender: TObject);
begin

if Capture = nil then

Capture := TSoundCaptureStream.Create(DXSound1.Driver);
Capture.SetPCMFormat(8000, 8, 1);
Capture.OnFilledBuffer := onFilled;
Capture.Start;
end;


procedure TForm1.onFilled(Sender: TObject);
var
sm:TMemoryStream;
begin

if Capture <> nil then

begin

sm :=TMemoryStream.Create;
try
Capture.Position := 0;
sm.CopyFrom(Capture,Capture.BufferLength);
sm.SaveToFile('1.wav');
Capture.Position := 0;
finally
sm.Free;
end;

end;

end;