Update InputFFT.ino (Ameba-AIoT#265)

- Increase sensitivity by adding a gain factor for audio buffer
- Add constrain to audio buffer to prevent overflow and loss of data

Author: pammyleong

Arduino_package/hardware/libraries/AudioCodec/examples/InputFFT/InputFFT.ino

@@ -12,11 +12,13 @@
 
 #define SAMPLERATE 16000
 #define SAMPLECOUNT 128
+#define GAIN_FACTOR 1.0  // Gain factor (can be adjusted), Cannot be 0 as it will mute the signal
 
 int16_t audio_buffer[SAMPLECOUNT] = {0};
 float fft_buffer[SAMPLECOUNT/2] = {0};
 uint16_t freq_bins[SAMPLECOUNT/2] = {0};
 int i = 0;
+int audioBufferMaxValue = INT16_MAX;  // 16-bit signed audio data (Refer to int16_t audio_buffer[SAMPLECOUNT])
 
 FFT fft;
 
@@ -38,6 +40,10 @@ void setup() {
 void loop() {
     if (Codec.readAvaliable()) {
         Codec.readDataPage(audio_buffer, SAMPLECOUNT);    // read latest received data from buffer
+        for (int i = 0; i < SAMPLECOUNT; i++) {
+            audio_buffer[i] *= constrain(audio_buffer[i] * GAIN_FACTOR, -audioBufferMaxValue, audioBufferMaxValue);  // Clamping to avoid overflow and amplify each sample
+        }
+        
         fft.calculate(audio_buffer, fft_buffer, SAMPLECOUNT);
         for (i = 0; i < (SAMPLECOUNT/2); i++) {
             if (fft_buffer[i] > 0.01) {