The requirement for the microphone is simply that it has a response that has some capability down to 20Hz with useable signal to noise ratio. The exact response is of no importance since that function is eliminated form influencing our process. We have found that the majority of modern phones and tablets meet this requirement. For those few that do not, it is possible to purchase a simple low cost calibrated mic that plugs into the mic input of the phone or tablet to give better performance.