Audio Library FFT with ADC input

[markvr]

I'm using the new Audio library from Paul to sample from an analog pin and perform an FFT. It works great, and is far simpler (and I imagine vastly more CPU efficient) that my original efforts of simply looping with analogRead().

I'm curious though at what frequency does it sample at, and can I change this?

Also for anyone else doing similar things it seems to have a low volume cutoff, where below a certain volume level all the outputs read 0. I've had look in input_adc.cpp, and there are two lines:

analogReference(INTERNAL); // range 0 to 1.2 volts
//analogReference(DEFAULT); // range 0 to 3.3 volts

I'm using a mic/opamp breakout board from Adafruit, which outputs from 0 to V (where V is the input it's powered with, i.e in my case 3.3v) with a dc bias at V/2, and so for me swapping these lines around to range from 0-3.3 made it much more sensitive.

Thanks!
Mark

 

[PaulD]

good tip! tnx..

 

[markvr]

Have just worked out the bit about the frequency, there is a define in util.h of:
// 48e6 / 44100
#define PDB_PERIOD 1087

So it's unsurprisingly 44.1khz, and presumably can changed as above!