FFT unavailable

[degalatis]

Hi-

I am unable to get an output to the FFT in the example program "FFT Test" after making a small change.
The only addition to the program is adding a line in void loop, serial.print(myFFT.available()). Adding this line causes the myFFT.available() to always return 0.

Any ideas on how to fix this?

My current hardware is the Teensy 4.1. I am also using the Audio Shield (for Teensy 4).
Here is the example program, with the change made.

// FFT Test
//
// Compute a 1024 point Fast Fourier Transform (spectrum analysis)
// on audio connected to the Left Line-In pin.  By changing code,
// a synthetic sine wave can be input instead.
//
// The first 40 (of 512) frequency analysis bins are printed to
// the Arduino Serial Monitor.  Viewing the raw data can help you
// understand how the FFT works and what results to expect when
// using the data to control LEDs, motors, or other fun things!
//
// This example code is in the public domain.

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

const int myInput = AUDIO_INPUT_LINEIN;
//const int myInput = AUDIO_INPUT_MIC;

// Create the Audio components.  These should be created in the
// order data flows, inputs/sources -> processing -> outputs
//
AudioInputI2S          audioInput;         // audio shield: mic or line-in
AudioSynthWaveformSine sinewave;
AudioAnalyzeFFT1024    myFFT;
AudioOutputI2S         audioOutput;        // audio shield: headphones & line-out

// Connect either the live input or synthesized sine wave
AudioConnection patchCord1(audioInput, 0, myFFT, 0);
//AudioConnection patchCord1(sinewave, 0, myFFT, 0);

AudioControlSGTL5000 audioShield;

void setup() {
  // Audio connections require memory to work.  For more
  // detailed information, see the MemoryAndCpuUsage example
  AudioMemory(12);

  // Enable the audio shield and set the output volume.
  audioShield.enable();
  audioShield.inputSelect(myInput);
  audioShield.volume(0.5);

  // Configure the window algorithm to use
  myFFT.windowFunction(AudioWindowHanning1024);
  //myFFT.windowFunction(NULL);

  // Create a synthetic sine wave, for testing
  // To use this, edit the connections above
  sinewave.amplitude(0.8);
  sinewave.frequency(1034.007);
}

void loop() {
  float n;
  int i;
  int test;
  [B]Serial.print(myFFT.available());[/B]
  if (myFFT.available()) {
    // each time new FFT data is available
    // print it all to the Arduino Serial Monitor
    
    Serial.print("FFT: ");
    for (i=0; i<40; i++) {
      n = myFFT.read(i);
      if (n >= 0.01) {
        Serial.print(n);
        Serial.print(":) ");
      } else {
        Serial.print("  -  "); // don't print "0.00"
      }
    }
    Serial.println();
  }
}

Here is the output on the serial monitor

 

[thebigg]

If it actually compiles, then I assume the bolded line should read

Serial.print(myFFT.available());

 

[thebigg]

Then, if you look at the source

bool available() {
	if (outputflag == true) {
		outputflag = false;
		return true;
	}
	return false;
}

This means that available() will only return true once as it is reset to false each time.

 

[degalatis]

Oh... that makes so much sense...
Thank you.

 

[MarkT]

It would be less confusing if its name reflected that's its stateful, such as receive().