Here's the deal, I'm attempting to learn how to use an FFT (Fast Fourier Transformation) Library for sound analysis (link is here). My issue is that this comes with included C++ code to show users how to use the FFT library. There are three examples, but I'll show this one because it's closest to the application I have planned for it:
/*
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(115200); // 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
}
}
}
Now, with that said, I have a very general grasp of the idea that those lines referencing some variable called ADMUX and ADCSRA have to do with the analogRead() method and that the ADCH and ADCL refer to another two components that are combined to provide the returned integer that analogRead() spits out. What I don't understand whatsoever are those seemingly random strings of characters that these are being set equal to. For example, what does 0x40 or 0x01 or 0xe5 even refer to in the setup() method (if nothing else maybe somebody could point me in the right direction for this, because that part I really am entirely clueless about). And furthermore, why manipulate these directly in the first place, because if you reference the source code for analogRead() they look awfully similar. Thanks for any help in advance!
