From 6fd48f28154d60d402743795028b5aa6d316a0db Mon Sep 17 00:00:00 2001
From: Ahmet Inan <xdsopl@googlemail.com>
Date: Tue, 13 Jan 2015 20:26:27 +0100
Subject: [PATCH] do rms compression again .. removed analyzer normalization

it makes the spectrum visualization less colorful, but a lot clearer.
---
 app/src/main/rs/decoder.rs | 5 +++--
 app/src/main/rs/stft.rsh   | 7 ++-----
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/app/src/main/rs/decoder.rs b/app/src/main/rs/decoder.rs
index 77b8593..79222ac 100644
--- a/app/src/main/rs/decoder.rs
+++ b/app/src/main/rs/decoder.rs
@@ -212,12 +212,13 @@ void decode(int samples) {
     *saved_height = 0;
     for (int sample = 0; sample < samples; ++sample, ++buffer_pos) {
         int amp = audio_buffer[sample];
-        float avg_amp = filter(&avg_amplitude, abs(amp));
+        float avg_rms = filter(&avg_amplitude, amp * amp);
+        float avg_amp = sqrt(2.0f * avg_rms);
         if (avg_amp < 16.0f)
             continue;
         float norm_amp = amp / avg_amp;
 
-        spectrum_analyzer(amp);
+        spectrum_analyzer(127.0f * norm_amp);
 
         complex_t cnt_baseband = convert(&cnt_ddc, norm_amp);
         complex_t dat_baseband = convert(&dat_ddc, norm_amp);
diff --git a/app/src/main/rs/stft.rsh b/app/src/main/rs/stft.rsh
index ed32bd1..80388d4 100644
--- a/app/src/main/rs/stft.rsh
+++ b/app/src/main/rs/stft.rsh
@@ -76,7 +76,7 @@ static void spectrum_analyzer(int amplitude)
 #endif
 
     buffer[n] = amplitude;
-    if (!((++n)%(radix2_N))) {
+    if (!(++n&(radix2_N-1))) {
         n &= stft_N - 1;
         for (int i = 0; i < stft_N; ++i)
             input[i&(radix2_N-1)] += complex(stft_w[i] * buffer[(i+n)&(stft_N-1)], 0.0f);
@@ -84,15 +84,12 @@ static void spectrum_analyzer(int amplitude)
         radix2(output, input, radix2_N, 1, 0);
         for (int i = 0; i < radix2_N; ++i)
             input[i] = 0.0f;
-        float maximum = 0.0f;
-        for (int i = 0; i < radix2_N; ++i)
-            maximum = max(maximum, cabs(output[i]));
         for (int j = spectrum_height - 1; 0 < j; --j)
             for (int i = 0; i < spectrum_width; ++i)
                 spectrum_buffer[spectrum_width * j + i] = spectrum_buffer[spectrum_width * (j-1) + i];
         for (int i = 0; i < spectrum_width; ++i) {
             int b = (i * (radix2_N / 2)) / spectrum_width;
-            float power = clamp(pown(cabs(output[b]) / maximum, 2), 0.0f, 1.0f);
+            float power = clamp(pown(cabs(output[b]) / 127.0f, 2), 0.0f, 1.0f);
             float dB = 10.0f * log10(max(0.000001f, power));
             float v = clamp((60.0f + dB) / 60.0f, 0.0f, 1.0f);
             spectrum_buffer[i] = rainbow(v);