[igt-dev] [PATCH i-g-t 1/2] lib/igt_audio: fix synthesized signal amplitude

[Simon Ser]

For each channel of the audio signal, we choose a set of frequencies to
generate. However we previously divided each sample by the total number of
frequencies, instead of the number of frequencies assigned to the channel we're
currently processing. This resulted in low amplitudes (0.5 instead of 1.0 for
2 channels).

This patch fixes this issue and sets the generated signal amplitude to 0.9.
Indeed, we want to detect if the receiver grows the signal, we don't want it
to get capped at 1.0 immediately.

Signed-off-by: Simon Ser <simon.ser at intel.com>
---
 lib/igt_audio.c | 33 ++++++++++++++++++++++++++++-----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/lib/igt_audio.c b/lib/igt_audio.c
index 90d16fe4bd11..f6c8e399e345 100644
--- a/lib/igt_audio.c
+++ b/lib/igt_audio.c
@@ -36,6 +36,8 @@
 #include "igt_core.h"
 
 #define FREQS_MAX 64
+#define CHANNELS_MAX 8
+#define SYNTHESIZE_AMPLITUDE 0.9
 
 /**
  * SECTION:igt_audio
@@ -77,6 +79,8 @@ struct audio_signal *audio_signal_init(int channels, int sampling_rate)
 {
 	struct audio_signal *signal;
 
+	igt_assert(channels <= CHANNELS_MAX);
+
 	signal = malloc(sizeof(struct audio_signal));
 	memset(signal, 0, sizeof(struct audio_signal));
 
@@ -156,7 +160,7 @@ void audio_signal_synthesize(struct audio_signal *signal)
 
 		for (j = 0; j < period_len; j++) {
 			value = 2.0 * M_PI * freq / signal->sampling_rate * j;
-			value = sin(value) / signal->freqs_count;
+			value = sin(value) * SYNTHESIZE_AMPLITUDE;
 
 			period[j] = value;
 		}
@@ -195,6 +199,20 @@ void audio_signal_reset(struct audio_signal *signal)
 	signal->freqs_count = 0;
 }
 
+static size_t audio_signal_count_freqs(struct audio_signal *signal, int channel)
+{
+	size_t n, i;
+	struct audio_signal_freq *freq;
+
+	for (i = 0; i < signal->freqs_count; i++) {
+		freq = &signal->freqs[i];
+		if (freq->channel < 0 || freq->channel == channel)
+			n++;
+	}
+
+	return n;
+}
+
 /**
  * audio_signal_fill:
  * @signal: The target signal structure
@@ -208,14 +226,18 @@ void audio_signal_reset(struct audio_signal *signal)
 void audio_signal_fill(struct audio_signal *signal, double *buffer,
 		       size_t samples)
 {
-	double *destination, *source;
+	double *dst, *src;
 	struct audio_signal_freq *freq;
 	int total;
 	int count;
 	int i, j, k;
+	size_t freqs_per_channel[CHANNELS_MAX];
 
 	memset(buffer, 0, sizeof(double) * signal->channels * samples);
 
+	for (i = 0; i < signal->channels; i++)
+		freqs_per_channel[i] = audio_signal_count_freqs(signal, i);
+
 	for (i = 0; i < signal->freqs_count; i++) {
 		freq = &signal->freqs[i];
 		total = 0;
@@ -223,8 +245,8 @@ void audio_signal_fill(struct audio_signal *signal, double *buffer,
 		igt_assert(freq->period);
 
 		while (total < samples) {
-			source = freq->period + freq->offset;
-			destination = buffer + total * signal->channels;
+			src = freq->period + freq->offset;
+			dst = buffer + total * signal->channels;
 
 			count = freq->period_len - freq->offset;
 			if (count > samples - total)
@@ -238,7 +260,8 @@ void audio_signal_fill(struct audio_signal *signal, double *buffer,
 					if (freq->channel >= 0 &&
 					    freq->channel != k)
 						continue;
-					destination[j * signal->channels + k] += source[j];
+					dst[j * signal->channels + k] +=
+						src[j] / freqs_per_channel[k];
 				}
 			}
 
-- 
2.21.0