Oscillograph with 1.8" TFT
With the TFT library comes the example sketch TFTGraph which shows the signal connected to analog input A0.
But even if you remove the delay(16) it still is rather slow due to the fact
that each value is written to the screen immediately after reading and the complete screen is erased after
the right margin of the screen is reached.
If you omit these time-consuming tasks you get a much faster display.
Download the source
If you want to connect a microphone to your arduino have a look at my