FFT256 needs 23 ms on Teensy 3.1 @72Mhz ?

[Kukulkan]

Hello,

I'm new to the board and hope to get some help here in the next time. As I'm absolutely new to microcontroller development (but not to software development), I will have some questions. Here is the first today

I'm using Audio Board and do some FFT and display some LED Matrix stuff. I realized, that the FFT only provides data every 23ms. As I like to do some real-time reaction later, this seems very slow. I found some people in other forums telling that FFT with 256 only needs about 6 to 9ms on some 16Mhz device. Sadly I dont find it anymore.

Is there a way to enhance the speed a little? Something around 12ms will be sufficient.

This is my reduced source:

#include <Wire.h>
#include "Adafruit_LEDBackpack.h"
#include "Adafruit_GFX.h"
#include <Metro.h>
#include <Audio.h>
#include <SPI.h>
#include <SD.h>

// Initialize related values
const int myInput = AUDIO_INPUT_LINEIN;


// Define objects
Adafruit_8x8matrix matrix = Adafruit_8x8matrix();
Metro tMatrix = Metro(60); // speed of scrolling
AudioInputI2S          audioInput;         // audio shield: mic or line-in
AudioAnalyzeFFT256     myFFT;
AudioOutputI2S         audioOutput;        // audio shield: headphones & line-out
AudioControlSGTL5000   audioShield;
elapsedMillis sinceTest1;

// Connect the live input
AudioConnection patchCord1(audioInput, 0, myFFT, 0);

// Define constants

// Set global variables
int matrixCounter = 10;
float level[11];
int lastTime = 0;

void setup() {
	// *** init serial interface for debug ***
	Serial.begin(9600);
	
	// *** Init audio ***
	AudioMemory(12);
    
	// Enable the audio shield and set the output volume.
	audioShield.enable();
	audioShield.inputSelect(myInput);
	audioShield.volume(0.5);
	audioShield.lineInLevel(5);

	// Configure the window algorithm to use
	myFFT.windowFunction(AudioWindowWelch256);
	
	// *** init matrix display ***
	matrix.begin(0x70);  // pass in the address
	matrix.setRotation(2);
	matrix.clear();
	
	lastTime = sinceTest1;
}

void loop() {
	if (myFFT.available()) {
		doFFT(); // do FFT
		Serial.print(sinceTest1 - lastTime);
		Serial.println("ms");
		lastTime = sinceTest1;
	}
}

void doFFT() {
	// each time new FFT data is available
	// do some stuff with the FFT data
	
}

Is there something I can enhance?

Best,

Kukulkan

 

[el_supremo]

By default, the library averages 8 consecutive FFT outputs before making it available. There is an averageTogether function/method which allows you to change the default, so give 1 a try.
I suspect that the faster times reported by others were for code which does not average successive FFTs before generating an output.

Pete

 

[Kukulkan]

Ah, yes. I've seen this function but I assumed it to be 0 if not set. The documentation misses the information that this value is 8 by default.

Setting this to 4 or even 3 returned in much faster responses (12ms and 9ms).

Thank you for that hint, problem solved,

Kukulkan