Predominant frequency identification with FFT

[yannbec]

HI,

All this is based on the FFT tutorial in the audio tutorial of Teensy with its audio shield.

I'm trying a simple code in order to identifie in real time the predominant frequency in a complexe sound. In a FOR loop, I compare each FFT value at each 43Hz to get at the end of the loop the highest value and then print it in the monitor.
So if I simply ask it to print the value each time it gets a new higher value while being in one step of the loop, the code works and I get in the monitor in each line all the highest frequencies in the sample with the highest one at the end of the line. So for each sample I will get 0 (initiale value in HZ) then 43 (first test) and then some other frequencies that the code founds in the FFT higher than the 43HZ value. I compare the value of the FFT but I print the frequency that correspond to the value.



But I would like only to get the highest value of the sample and print it at the end of the FOR loop. So I tried the program below and it doesn't work (I've put in red my modifications). The monitor only gives "FFT : -" on each line as if the "c" value I test in the code always got to the initial value "0"... I don't understand why. Could someone help me please? thx!

#include <Audio.h>
#include <Wire.h>
#include <SPI.h>
#include <SD.h>
#include <SerialFlash.h>

// GUItool: begin automatically generated code
AudioInputI2S i2s2; //xy=280,253
AudioSynthWaveform waveform1; //xy=452,228
AudioMixer4 mixer1; //xy=459,307
AudioAnalyzeFFT1024 fft1024_1; //xy=658,324
AudioOutputI2S i2s1; //xy=659,254
AudioConnection patchCord1(i2s2, 0, mixer1, 0);
AudioConnection patchCord2(i2s2, 1, mixer1, 1);
AudioConnection patchCord3(waveform1, 0, i2s1, 0);
AudioConnection patchCord4(waveform1, 0, i2s1, 1);
AudioConnection patchCord5(mixer1, fft1024_1);
AudioControlSGTL5000 sgtl5000_1; //xy=321,382
// GUItool: end automatically generated code


void setup() {
Serial.begin(9600);
AudioMemory(10);
sgtl5000_1.enable();
sgtl5000_1.volume(0.5);
sgtl5000_1.inputSelect(AUDIO_INPUT_MIC);
sgtl5000_1.micGain(20);
mixer1.gain(0, 0.5);
mixer1.gain(1, 0.5);
mixer1.gain(2, 0.5);
waveform1.begin(0.5,440,WAVEFORM_PULSE);
delay(1000);
}


void loop() {
float c = 0 ;
float a = 0 ;

if (fft1024_1.available()) {

Serial.print("FFT: ");
for (int i=0; i<50; i++) { // 0-25 --> DC to 1.25 kHz
float n = fft1024_1.read(i);

if ( n > a ) {
a = n ;
c = i*43 ;

if (i=50){
printNumber(c);
waveform1.begin(0.5,c ,WAVEFORM_PULSE);
}

}
else{

}


}

Serial.println();
}
else{
waveform1.begin(0,440,WAVEFORM_PULSE);
}
}

void printNumber(float n) {

if (n >= 0.004) {
Serial.print(n, 3);
Serial.print(" ");
} else {
Serial.print(" - "); // don't print "0.00"
}

}

 

[el_supremo]

Your first problem is that this:

        if (i = 50) {

does not test if i equals 50, it sets i to 50. Use:

        if (i == 50) {

Second, your for loop index goes up to i<50 so i can never equal 50 inside the loop which makes this statement redundant.

Change all of this:

if (fft1024_1.available()) {

Serial.print("FFT: ");
for (int i=0; i<50; i++) { // 0-25 --> DC to 1.25 kHz
float n = fft1024_1.read(i);

if ( n > a ) {
a = n ;
c = i*43 ;

if (i=50){
printNumber(c);
waveform1.begin(0.5,c ,WAVEFORM_PULSE);
}

}
else{

}


}

Serial.println();
}
else{
waveform1.begin(0,440,WAVEFORM_PULSE);
}

to this:

  if (fft1024_1.available()) {
    for (int i = 0; i < 50; i++) { // 0-25 --> DC to 1.25 kHz
      float n = fft1024_1.read(i);
      if ( n > a ) {
        a = n ;
        c = i * 43 ;
      }
    }
    Serial.print("FFT: ");
    printNumber(c);
    Serial.println();
    waveform1.begin(0.5, c , WAVEFORM_PULSE);
  } else {
    waveform1.begin(0, 440, WAVEFORM_PULSE);
  }

Also note the indenting I've added which makes the code more readable. It is easy to indent your code using the IDE. Just select Tools|Auto Format (or you can just type Control-T).

Pete

 

[yannbec]

Thank you so much the code now works except for the waveform generation that does pretty much nothing but some "pop" some times.

Any ideas? Thank you again Pete.

 

[el_supremo]

I think your problem is that you are calling waveform1.begin every time through the loop function which probably keeps restarting the waveform which can cause a click.
Remove this part of the code (note that the end brace '}' before the 'else' is not removed):

else {
    waveform1.begin(0, 440, WAVEFORM_PULSE);
  }

so that you only change the waveform if you detect a different frequency. In fact, it might be a good idea to add some code in the loop so that you remember the last value of 'c' that was used to begin a new waveform and only call begin again if the value of 'c' has changed. That should also reduce any clicks in the audio.

Pete

 

[PaulStoffregen]

I'm trying a simple code in order to identifie in real time the predominant frequency in a complexe sound.

Usually the YIN algorithm works much better than FFT for this application. Use the NoteFrequency object. Look at File > Examples > Audio > Analysis > NoteFrequency.

 

[yannbec]

Thank you it works now. Another problem was the Audiomemory was set to only 10. I changed it for 30 and now the sine generation works.

 

[yannbec]

Paul, thank you the YIN algorithm is really accurate about the frequency ! but I lose the level information I got with the FFT. How could I mesure it so I can associate a frequency with a volume level while using the YIN ?