To measure sound waves with the ADC-40 you will need a microphone connected which you will connect to a BNC.
To source the BNC connector try:
The microphone cables can be soldered onto the BNC. The microphone will recieve the noise and create a voltage. To generate higher voltages you may need to use a powered microphone.
The voltage may be very low with slight changes, so you may have to amplify the signal coming from the microphone if you decide against a powered one, as the ADC-40 has an 8 bit resolution and can only detect changes of 39 mV. The sound waves frequency should not exceed the ADC-40's bandwidth otherwise you will not capture it.