I just started using Pd and had the idea of inputting songs and using their dB level to output a corresponding frequency. What would be the best way to go about doing this? Thanks in advance.

What do you want to do with it? That'll probably affect how you end up designing it.

You can get the audio either in through adc~ if it's external to your computer or readfs~ to play a file on the hard drive. Hook those up to env~ and you'll get the dB of the input. Do whatever kind of math you need to do on it to convert it into the range you want and then feed that into some kind of oscillator.. You could also just feed it into a mtof since the dB values will already overlap with a good chunk of possible midi note values.