Since no one ever responded I will answer this as to how I eventually did it. I used an image and the microphone's activityLevel attribute to show the the real time sound input to the microphone. Since this activityLevel is not bindable I had to use a timer.
Also do remember to get a valid value of activityLevel apart from calling
microphone = Microphone.getMicrophone();
Otherwise the activityLevel value is -1 The second point is not mentioned in flex docs