I am trying to use the FFT library to take in a song or sound, fill the frequency bins, and flash LEDs depending on which bins are the most full. I am completely new to arduino and need some help understanding the example that comes with the FFT library I downloaded (ArduinoFFT - Open Music Labs Wiki).

I have a circuit set up that inputs a song’s electrical signals into Analog0. My problem is that regardless of whether or not the song is playing (or even if the circuit it set up or not), the arduino continuously outputs numbers to the serial monitor. So my primary question is: What is inducing this output if nothing is plugged in and how can I fix it? My next question (if I fix it so that I am getting real output) would be: What is the best way to capture the incoming data so I can visualize the bins and make decisions about which LEDs to flash?

I am used to working with matlab so bear with me!

Thanks in advance!

```
/*
fft_adc_serial.pde
guest openmusiclabs.com 7.7.14
example sketch for testing the fft library.
it takes in data on ADC0 (Analog0) and processes them
with the fft. the data is sent out over the serial
port at 115.2kb.
*/
#define LOG_OUT 1 // use the log output function
#define FFT_N 256 // set to 256 point fft
#include <FFT.h> // include the library
void setup() {
Serial.begin(9600); // use the serial port
TIMSK0 = 0; // turn off timer0 for lower jitter
ADCSRA = 0xe5; // set the adc to free running mode
ADMUX = 0x40; // use adc0
DIDR0 = 0x01; // turn off the digital input for adc0
}
void loop() {
while(1) { // reduces jitter
cli(); // UDRE interrupt slows this way down on arduino1.0
for (int i = 0 ; i < 512 ; i += 2) { // save 256 samples
while(!(ADCSRA & 0x10)); // wait for adc to be ready
ADCSRA = 0xf5; // restart adc
byte m = ADCL; // fetch adc data
byte j = ADCH;
int k = (j << 8) | m; // form into an int
k -= 0x0200; // form into a signed int
k <<= 6; // form into a 16b signed int
fft_input[i] = k; // put real data into even bins
fft_input[i+1] = 0; // set odd bins to 0
}
fft_window(); // window the data for better frequency response
fft_reorder(); // reorder the data before doing the fft
fft_run(); // process the data in the fft
fft_mag_log(); // take the output of the fft
sei();
Serial.println("start");
for (byte i = 0 ; i < FFT_N/2 ; i++) {
Serial.println(fft_log_out[i]); // send out the data
}
//Serial.write(255); // send a start byte
//Serial.write(fft_log_out, 128); // send out the data
}
}
```