annotate examples/02-Digital/level-meter/render.cpp @ 538:58652b93ef7e prerelease

Converted some spaces to tabs

/*
 ____  _____ _        _    
| __ )| ____| |      / \   
|  _ \|  _| | |     / _ \  
| |_) | |___| |___ / ___ \ 
|____/|_____|_____/_/   \_\

The platform for ultra-low latency audio and sensor processing

http://bela.io

A project of the Augmented Instruments Laboratory within the
Centre for Digital Music at Queen Mary University of London.
http://www.eecs.qmul.ac.uk/~andrewm

(c) 2016 Augmented Instruments Laboratory: Andrew McPherson,
  Astrid Bin, Liam Donovan, Christian Heinrichs, Robert Jack,
  Giulio Moro, Laurel Pardue, Victor Zappi. All rights reserved.

The Bela software is distributed under the GNU Lesser General Public License
(LGPL 3.0), available here: https://www.gnu.org/licenses/lgpl-3.0.txt
*/


#include <Bela.h>
#include <cmath>

#define NUMBER_OF_SEGMENTS	10

// Two levels of audio: one follows current value, the other holds
// peaks for longer
float gAudioLocalLevel = 0, gAudioPeakLevel = 0;

// Decay rates for detecting levels
float gLocalDecayRate = 0.99, gPeakDecayRate = 0.999;

// Thresholds for LEDs: set in setup()
float gThresholds[NUMBER_OF_SEGMENTS + 1];
int gSamplesToLight[NUMBER_OF_SEGMENTS];

// High-pass filter on the input
float gLastX[2] = {0};
float gLastY[2] = {0};

// These coefficients make a high-pass filter at 5Hz for 44.1kHz sample rate
double gB0 = 0.99949640;
double gB1 = -1.99899280;
double gB2 = gB0;
double gA1 = -1.99899254;
double gA2 = 0.99899305;

bool setup(BelaContext *context, void *userData)
{	
	// This project makes the assumption that the audio and digital
	// sample rates are the same. But check it to be sure!
	if(context->audioFrames != context->digitalFrames) {
		rt_printf("Error: this project needs the audio and digital sample rates to be the same.\n");
		return false;
	}
	
	// Initialise threshold levels in -3dB steps. One extra for efficiency in render()
	// Level = 10^(dB/20)
	for(int i = 0; i < NUMBER_OF_SEGMENTS + 1; i++) {
		gThresholds[i] = powf(10.0f, (-1.0 * (NUMBER_OF_SEGMENTS - i)) * .05);
	}
	
	for(int i = 0; i < NUMBER_OF_SEGMENTS; i++) {
		gSamplesToLight[i] = 0;
		pinMode(context, 0, i, OUTPUT);
	}

	return true;
}

void render(BelaContext *context, void *userData)
{
	for(unsigned int n = 0; n < context->audioFrames; n++) {
		// Get average of audio input channels
		float sample = 0;
		for(unsigned int ch = 0; ch < context->audioChannels; ch++) {
			context->audioOut[n * context->audioChannels + ch] = 
				context->audioIn[n * context->audioChannels + ch];
			sample += context->audioIn[n * context->audioChannels + ch];
		}
		
		// Do DC-blocking on the sum
		float out = gB0 * sample + gB1 * gLastX[0] + gB2 * gLastX[1]
						- gA1 * gLastY[0] - gA2 * gLastY[1];

		gLastX[1] = gLastX[0];
		gLastX[0] = sample;
		gLastY[1] = gLastY[0];
		gLastY[0] = out;
		
		out = fabsf(out / (float)context->audioChannels);
		
		// Do peak detection: fast-responding local level
		if(out > gAudioLocalLevel)
			gAudioLocalLevel = out;
		else
			gAudioLocalLevel *= gLocalDecayRate;
		
		// Do peak detection: slow-responding peak level
		if(out > gAudioPeakLevel)
			gAudioPeakLevel = out;
		else {
			// Make peak decay slowly by only multiplying
			// every few samples
			if(((context->audioFramesElapsed + n) & 31) == 0)
				gAudioPeakLevel *= gPeakDecayRate;
		}	
		// LED bargraph on digital outputs 0-9
		for(int led = 0; led < NUMBER_OF_SEGMENTS; led++) {
			// All LEDs up to the local level light up. The LED
			// for the peak level also remains lit.
			int state = LOW;
				
			if(gAudioLocalLevel > gThresholds[led]) {
				state = HIGH;
				gSamplesToLight[led] = 1000;
			}
			/*else if(gAudioPeakLevel > gThresholds[led] && gAudioPeakLevel <= gThresholds[led + 1]) {
				state = HIGH;
				gSamplesToLight[led] = 1000;
			}*/
			else if(--gSamplesToLight[led] > 0)
				state = HIGH;
			
			// Write LED
			digitalWriteOnce(context, n, led, state);
		}
	}
}

void cleanup(BelaContext *context, void *userData)
{

}