我正在尝试使用mbed LPC微控制器对吉他进行调音。
以下是该项目示例的链接。
https://developer.mbed.org/users/adurand/notebook/guitar-tuner/
但是，我有一些问题。首先，我使用任意波形发生器以每个弦的所需频率模拟吉他输入。放大电路的结构相同。我还更改了代码，以使用Mbed LCD代替诺基亚。我已经使用示波器来验证输入到Mbed的AnalogueIn p20的输出是否已放大并处于正确的频率。这是我遇到的问题。
这是代码（归功于Andrew Durand）：
#include "mbed.h"
#include "adc.h"
#include "C12832.h"
#include <math.h>
#define PI 3.1415
#define SAMPLE_RATE 24000
InterruptIn button1(p12);
C12832 lcd(p5, p7, p6, p8, p11);
DigitalOut myled1(LED1);
DigitalOut myled2(LED2);
DigitalOut myled3(LED3);
//LCD and Other Random Variables
int string_select = 0;
float high, high1, in_tune, in_tune1, in_tune2, in_tune3,
low, low1, note, low_mod, high_mod;
char* key;
int Counter = 0;
int Buffer[6000];
float goertzelFilter(int samples[], float freq, int N) {
float s_prev = 0.0;
float s_prev2 = 0.0;
float coeff,normalizedfreq,power,s;
int i;
normalizedfreq = freq / SAMPLE_RATE;
coeff = 2*cos(2*PI*normalizedfreq);
for (i=0; i<N; i++) {
s = samples[i] + coeff * s_prev - s_prev2;
s_prev2 = s_prev;
s_prev = s;
}
power = s_prev2*s_prev2+s_prev*s_prev-coeff*s_prev*s_prev2;
return power;
}
ADC adc(SAMPLE_RATE, 1);
void sample_audio(int chan, uint32_t value) {
Buffer[Counter] = adc.read(p20);
Counter += 1;
}
void button1_pressed() {
string_select++;
if (string_select > 5) string_select = 0;
}
int main() {
//Interupt for Switching Strings
button1.mode(PullDown);
button1.rise(&button1_pressed);
while (1) {
switch (string_select) {
case 0:
note = 82;
key= "E2";
break;
case 1:
note = 110;
key= "A2";
break;
case 2:
note = 147;
key= "D3";
break;
case 3:
note = 196;
key= "G3";
break;
case 4:
note = 247;
key= "B3";
break;
case 5:
note = 330;
key= "E4";
break;
}
//Prepare for burst mode on all ADC pins and set up interrupt handler (using ADC library from Simon Blandford
adc.append(sample_audio);
adc.startmode(0,0);
adc.burst(1);
adc.setup(p20,1);
//start the interrupt and wait for about 4096 samples
adc.interrupt_state(p20,1);
wait(.2);
//Finsh up - Unset pin 20
adc.interrupt_state(p20,0);
adc.setup(p20,0);
int actual_rate = adc.actual_sample_rate();
//for debugging tell the terminal sample rate and how many samples we took
printf("Requested max sample rate is %u, actual max sample rate is %u.\n",
SAMPLE_RATE, actual_rate);
printf("We did %i samples\n",Counter);
high = 0;
low = 0;
for (int i=3; i<46; i+=3) {
high1 = goertzelFilter(Buffer, (note + i ), Counter);
if (high1 > high) high=high1;
}
for (int i=3; i<46; i+=3) {
low1 = goertzelFilter(Buffer, (note - i ), Counter);
if (low1 > low) low=low1;
}
in_tune1 = goertzelFilter(Buffer, (note+1), Counter);
in_tune2 = goertzelFilter(Buffer, note, Counter);
in_tune3 = goertzelFilter(Buffer, (note-1), Counter);
if ((in_tune1 > in_tune2) && (in_tune1 > in_tune3)) in_tune = in_tune1;
else if ((in_tune2 > in_tune1) && (in_tune2 > in_tune3)) in_tune = in_tune2;
else in_tune = in_tune3;
printf("high = %.2f, low = %.2f, in_tune = %.2f", high, low, in_tune);
high_mod = high/in_tune;
low_mod = low/in_tune;
if ((high_mod > .8)&&(low_mod > .8)) {
myled1 = 0;
myled2 = 0;
myled3 = 0;
}
if ((high_mod < .8)&&(low_mod > .8)) {
myled1 = 0;
myled2 = 0;
myled3 = 0;
}
if ((high > in_tune) && (low < in_tune)) { //Guitar string is at correct frequency
myled1 = 0;
myled2 = 1;
myled3 = 0;
} else if (high > in_tune) { // String is higher than the desired frequency
myled1 = 1;
myled2 = 0;
myled3 = 0;
} else if (low < in_tune){ // String is below that of the desired frequency
myled1 = 0;
myled2 = 0;
myled3 = 1;
} else { // Else no input, display squiggles
myled1 = 0;
myled2 = 0;
myled3 = 0;
}
// Display on the LCD
lcd.cls();
lcd.locate(0,0);
lcd.printf("Tuning String: %i", (6-string_select));
lcd.locate(0,11);
lcd.printf("%s at %i Hz",key, (int) note);
lcd.locate(0,23);
if (myled2) lcd.printf("In Tune!"); // if myled2 is on, guitar is in tune
else if (myled3) lcd.printf("Too Low "); // if myled3 is on, guitar is lower than desired tone
else if (myled1) lcd.printf("Too High"); // if myled1 is on, guitar is higher than desired tone
else lcd.printf("No Input Detected"); // corresponds to led case 4 - no guitar input present
Counter = 0;
}
}
现在，当我编译程序时，将显示消息。但是，LED在“太高”，“太低”和波浪形之间交替显示。我将是第一个承认我不是最好的编码器的人，我将在整个暑假期间真正地工作。代码可能存在非常严重的问题，或者可能相对简单。感谢所有输入。
注意：我尚未连接面包板上的防抖动电路-它已连接至我未使用的诺基亚LCD。我可以使用mbed应用板上的操纵杆在1-6之间更改所需的字符串。这样可以吗？还是去抖电路至关重要？
再次感谢。
最佳答案
查找low的循环与以下代码中查找high的循环几乎相同：
high = 0;
low = 0;
for (int i=3; i<46; i+=3) {
high1 = goertzelFilter(Buffer, (note + i ), Counter);
if (high1 > high) high=high1;
}
for (int i=3; i<46; i+=3) {
low1 = goertzelFilter(Buffer, (note - i ), Counter);
if (low1 > low) low=low1;
}
我建议
low部分应该像这样low = FLT_MAX;
for (int i=3; i<46; i+=3) {
low1 = goertzelFilter(Buffer, (note - i ), Counter);
if (low1 < low) low=low1;
}
...尽管我可能会误以为
low的预期用途。