GUACAMOLE-934: Correct waveform calculation. Switch to triangle wave to reduce aliasing distortion.
diff --git a/src/protocols/rdp/beep.c b/src/protocols/rdp/beep.c
index 46e80fd..8fb5001 100644
--- a/src/protocols/rdp/beep.c
+++ b/src/protocols/rdp/beep.c
@@ -46,29 +46,30 @@
* @param buffer_size
* The number of bytes of PCM data to write to the given buffer.
*/
-static void guac_rdp_beep_fill_square_wave(unsigned char* buffer,
+static void guac_rdp_beep_fill_triangle_wave(unsigned char* buffer,
int frequency, int rate, int buffer_size) {
- int remaining = buffer_size;
- int current_value = GUAC_RDP_BEEP_AMPLITUDE;
- int pulse_width = rate / frequency / 2;
+ /* With the distance between each positive/negative peak and zero being the
+ * amplitude, and with the "bounce" between those peaks occurring once
+ * every two periods, the number of distinct states that the triangle wave
+ * function goes through is twice the peak-to-peak amplitude, or four times
+ * the overall amplitude */
+ const int wave_period = GUAC_RDP_BEEP_AMPLITUDE * 4;
- /* Repeatedly write pulses (whose widths are determined by the desired
- * frequency) until buffer space is exhausted */
- while (remaining > 0) {
+ /* With the number of distinct states being the wave_period defined above,
+ * the "bounce" point within that period is half the period */
+ const int wave_bounce_offset = wave_period / 2;
- /* Truncate pulse if insufficient space remains */
- int block_size = pulse_width;
- if (block_size > remaining)
- block_size = remaining;
+ for (int position = 0; position < buffer_size; position++) {
- /* Write blocks, alternating the sign of the amplitude of each
- * successive block */
- memset(buffer, current_value, block_size);
- current_value = -current_value;
+ /* Calculate relative position within the repeating portion of the wave
+ * (the portion with wave_period unique states) */
+ int wave_position = (position * frequency * wave_period / rate) % wave_period;
- buffer += block_size;
- remaining -= block_size;
+ /* Calculate state of the triangle wave function at the calculated
+ * offset, knowing in advance the relative location that the function
+ * should "bounce" */
+ *(buffer++) = abs(wave_position - wave_bounce_offset) - GUAC_RDP_BEEP_AMPLITUDE;
}
@@ -95,8 +96,8 @@
int buffer_size = audio->rate * duration / 1000;
unsigned char* buffer = malloc(buffer_size);
- /* Beep for given frequency/duration using a simple square wave */
- guac_rdp_beep_fill_square_wave(buffer, frequency, audio->rate, buffer_size);
+ /* Beep for given frequency/duration using a simple triangle wave */
+ guac_rdp_beep_fill_triangle_wave(buffer, frequency, audio->rate, buffer_size);
guac_audio_stream_write_pcm(audio, buffer, buffer_size);
free(buffer);
