The microprocessor provides internal reference voltages of either 1.1V or Vcc (5V on a Uno). Providing a reference voltage through AREF is strictly optional.
The tutorial says it won't work if you don't connect the AREF. Is that because the code is expecting a 3.3v reference? I guess I'll understand how all this works a lot more when I actually get the mic and can start trying it out and seeing what it does.
The microphone can run on 2.4V - 5V, and you match AREF to the supply voltage. We recommend using the 3.3V source on the arduino because it is the 'quietest'. That is, for analog measurements, the 5V supply is not quite as stable a reference as the 3.3V.
Because "5v" can jump around a bit based on the power source, where 3.3v is more strictly controlled by the hardware? So that means I can just solder a jumper straight across from 3.3v to AREF? Some of the images I saw in the non-ada tutorial had resistors. Were those to further fine tune the reference or for safety?