arybczak · Aug 21, 2024 · Mar 18, 2021 · Mar 20, 2021 · Mar 23, 2021 · Apr 9, 2021
diff --git a/doc/config b/doc/config
@@ -149,6 +149,11 @@
 #
 #visualizer_spectrum_hz_max = 20000
 #
+## Use log scaling for the frequency spectrum axes
+#
+#visualizer_spectrum_log_scale_x = yes
+#visualizer_spectrum_log_scale_y = yes
+#
 ##### system encoding #####
 ##
 ## ncmpcpp should detect your charset encoding but if it failed to do so, you

diff --git a/src/screens/visualizer.cpp b/src/screens/visualizer.cpp
@@ -96,7 +96,7 @@ Visualizer::Visualizer()
 	memset(m_fftw_input, 0, sizeof(double)*DFT_TOTAL_SIZE);
 	m_fftw_output = static_cast<fftw_complex *>(fftw_malloc(sizeof(fftw_complex)*m_fftw_results));
 	m_fftw_plan = fftw_plan_dft_r2c_1d(DFT_TOTAL_SIZE, m_fftw_input, m_fftw_output, FFTW_ESTIMATE);
-	m_dft_logspace.reserve(500);
+	m_dft_freqspace.reserve(500);
 	m_bar_heights.reserve(100);
 #	endif // HAVE_FFTW3_H
 }
@@ -108,7 +108,7 @@ void Visualizer::switchTo()
 	m_reset_output = true;
 	drawHeader();
 #	ifdef HAVE_FFTW3_H
-	GenLogspace();
+	GenFreqSpace();
 	m_bar_heights.reserve(w.getWidth());
 #	endif // HAVE_FFTW3_H
 }
@@ -122,7 +122,7 @@ void Visualizer::resize()
 	hasToBeResized = 0;
 	InitVisualization();
 #	ifdef HAVE_FFTW3_H
-	GenLogspace();
+	GenFreqSpace();
 	m_bar_heights.reserve(w.getWidth());
 #	endif // HAVE_FFTW3_H
 }
@@ -421,7 +421,7 @@ void Visualizer::DrawSoundEllipseStereo(const int16_t *buf_left, const int16_t *
 		auto c = toColor(sqrt(x*x + 4*y*y), radius, true);
 		w << NC::XY(left_half_width + x, top_half_height + y)
 		  << c
-		  << Config.visualizer_chars[1]
+		  << Config.visualizer_chars[0]
 		  << NC::FormattedColor::End<>(c);
 	}
 }
@@ -450,7 +450,7 @@ void Visualizer::DrawFrequencySpectrum(const int16_t *buf, ssize_t samples, size
 	const size_t win_width = w.getWidth();
 
 	size_t cur_bin = 0;
-	while (cur_bin < m_fftw_results && Bin2Hz(cur_bin) < m_dft_logspace[0])
+	while (cur_bin < m_fftw_results && Bin2Hz(cur_bin) < m_dft_freqspace[0])
 		++cur_bin;
 	for (size_t x = 0; x < win_width; ++x)
 	{
@@ -459,10 +459,10 @@ void Visualizer::DrawFrequencySpectrum(const int16_t *buf, ssize_t samples, size
 		// accumulate bins
 		size_t count = 0;
 		// check right bound
-		while (cur_bin < m_fftw_results && Bin2Hz(cur_bin) < m_dft_logspace[x])
+		while (cur_bin < m_fftw_results && Bin2Hz(cur_bin) < m_dft_freqspace[x])
 		{
 			// check left bound if not first index
-			if (x == 0 || Bin2Hz(cur_bin) >= m_dft_logspace[x-1])
+			if (x == 0 || Bin2Hz(cur_bin) >= m_dft_freqspace[x-1])
 			{
 				bar_height += m_freq_magnitudes[cur_bin];
 				++count;
@@ -476,8 +476,19 @@ void Visualizer::DrawFrequencySpectrum(const int16_t *buf, ssize_t samples, size
 		// average bins
 		bar_height /= count;
 
-		// log scale bar heights
-		bar_height = (20 * log10(bar_height) + DYNAMIC_RANGE + GAIN) / DYNAMIC_RANGE;
+		// apply scaling to bar heights
+		if (Config.visualizer_spectrum_log_scale_y) {
+			bar_height = (20 * log10(bar_height) + DYNAMIC_RANGE + GAIN) / DYNAMIC_RANGE;
+		} else {
+			// apply gain
+			bar_height *= pow(10, 1.8 + GAIN / 20);
+			// buff higher frequencies
+			bar_height *= log2(2 + x) * 80.0/win_width;
+			// moderately normalize the heights
+			bar_height = pow(bar_height, 0.65);
+
+			//bar_height = pow(10, 1 + GAIN / 20) * bar_height;
+		}
 		// Scale bar height between 0 and height
 		bar_height = bar_height > 0 ? bar_height * height : 0;
 		bar_height = bar_height > height ? height : bar_height;
@@ -499,7 +510,12 @@ void Visualizer::DrawFrequencySpectrum(const int16_t *buf, ssize_t samples, size
 				++h_idx;
 		} else {
 			// data point does not exist, need to interpolate
-			h = Interpolate(x, h_idx);
+			if (Config.visualizer_spectrum_log_scale_x) {
+				h = InterpolateCubic(x, h_idx);
+			} else {
+				h = std::min(InterpolateLinear(x, h_idx), height / 1.0);
+				//h = 0;
+			}
 		}
 
 		for (size_t j = 0; j < h; ++j)
@@ -549,7 +565,7 @@ void Visualizer::DrawFrequencySpectrumStereo(const int16_t *buf_left, const int1
 	DrawFrequencySpectrum(buf_right, samples, height, w.getHeight() - height);
 }
 
-double Visualizer::Interpolate(size_t x, size_t h_idx)
+double Visualizer::InterpolateCubic(size_t x, size_t h_idx)
 {
 	const double x_next = m_bar_heights[h_idx].first;
 	const double h_next = m_bar_heights[h_idx].second;
@@ -594,6 +610,33 @@ double Visualizer::Interpolate(size_t x, size_t h_idx)
 	return h_next;
 }
 
+double Visualizer::InterpolateLinear(size_t x, size_t h_idx)
+{
+	const double x_next = m_bar_heights[h_idx].first;
+	const double h_next = m_bar_heights[h_idx].second;
+
+	double dh = 0;
+	if (h_idx == 0) {
+		// no data points on the left, linear extrapolation
+		if (h_idx < m_bar_heights.size()) {
+			const double x_next2 = m_bar_heights[h_idx+1].first;
+			const double h_next2 = m_bar_heights[h_idx+1].second;
+			dh = (h_next2 - h_next) / (x_next2 - x_next);
+		}
+		return h_next - dh * (x_next - x);
+	} else if (h_idx < m_bar_heights.size()) {
+		// simple linear interpolation
+		const double x_prev = m_bar_heights[h_idx-1].first;
+		const double h_prev = m_bar_heights[h_idx-1].second;
+
+		const double m = (h_next - h_prev) / (x_next - x_prev);
+		return h_prev + m * (x - x_prev);
+	}
+
+	// no data points on the right: don't interpolate
+	return h_next;
+}
+
 void Visualizer::ApplyWindow(double *output, const int16_t *input, ssize_t samples)
 {
 	// Use Blackman window for low sidelobes and fast sidelobe rolloff
@@ -622,10 +665,36 @@ void Visualizer::GenLogspace()
 	const size_t win_width = w.getWidth();
 	const size_t left_bins = (log10(HZ_MIN) - win_width*log10(HZ_MIN)) / (log10(HZ_MIN) - log10(HZ_MAX));
 	// Generate logspaced frequencies
-	m_dft_logspace.resize(win_width);
-	const double log_scale = log10(HZ_MAX) / (left_bins + m_dft_logspace.size() - 1);
-	for (size_t i = left_bins; i < m_dft_logspace.size() + left_bins; ++i) {
-		m_dft_logspace[i - left_bins] = pow(10, i * log_scale);
+	m_dft_freqspace.resize(win_width);
+	const double log_scale = log10(HZ_MAX) / (left_bins + m_dft_freqspace.size() - 1);
+	for (size_t i = left_bins; i < m_dft_freqspace.size() + left_bins; ++i) {
+		m_dft_freqspace[i - left_bins] = pow(10, i * log_scale);
+	}
+}
+
+// Generate vector of linearly-spaced frequencies from HZ_MIN to HZ_MAX
+void Visualizer::GenLinspace()
+{
+	// Calculate number of extra bins needed between 0 HZ and HZ_MIN
+	const size_t win_width = w.getWidth();
+	const size_t left_bins = (HZ_MIN - win_width * HZ_MIN) / (HZ_MIN - HZ_MAX);
+	// Generate linspaced frequencies
+	m_dft_freqspace.resize(win_width);
+	const double lin_scale = HZ_MAX / (left_bins + m_dft_freqspace.size() - 1);
+	for (size_t i = left_bins; i < m_dft_freqspace.size() + left_bins; ++i) {
+		m_dft_freqspace[i - left_bins] = i * lin_scale;
+	}
+}
+
+// Generate vector of spectrum frequencies from HZ_MIN to HZ_MAX
+// Frequencies are (not) log-scaled depending on
+// Config.visualizer_spectrum_log_scale_x
+void Visualizer::GenFreqSpace()
+{
+	if (Config.visualizer_spectrum_log_scale_x) {
+		GenLogspace();
+	} else {
+		GenLinspace();
 	}
 }
 #endif // HAVE_FFTW3_H

diff --git a/src/screens/visualizer.h b/src/screens/visualizer.h
@@ -76,8 +76,11 @@ struct Visualizer: Screen<NC::Window>, Tabbable
 	void DrawFrequencySpectrumStereo(const int16_t *, const int16_t *, ssize_t, size_t);
 	void ApplyWindow(double *, const int16_t *, ssize_t);
 	void GenLogspace();
+	void GenLinspace();
+	void GenFreqSpace();
 	double Bin2Hz(size_t);
-	double Interpolate(size_t, size_t);
+	double InterpolateCubic(size_t, size_t);
+	double InterpolateLinear(size_t, size_t);
 #	endif // HAVE_FFTW3_H
 
 	void InitDataSource();
@@ -114,7 +117,7 @@ struct Visualizer: Screen<NC::Window>, Tabbable
 	const double GAIN;
 	const std::wstring SMOOTH_CHARS;
 	const std::wstring SMOOTH_CHARS_FLIPPED;
-	std::vector<double> m_dft_logspace;
+	std::vector<double> m_dft_freqspace;
 	std::vector<std::pair<size_t, double>> m_bar_heights;
 
 	std::vector<double> m_freq_magnitudes;

diff --git a/src/settings.cpp b/src/settings.cpp
@@ -278,6 +278,8 @@ bool Configuration::read(const std::vector<std::string> &config_paths, bool igno
 			lowerBoundCheck<double>(result, Config.visualizer_spectrum_hz_min+1);
 			return result;
 			});
+	p.add("visualizer_spectrum_log_scale_x", &visualizer_spectrum_log_scale_x, "yes", yes_no);
+	p.add("visualizer_spectrum_log_scale_y", &visualizer_spectrum_log_scale_y, "yes", yes_no);
 	p.add("visualizer_color", &visualizer_colors,
 	      "blue, cyan, green, yellow, magenta, red", list_of<NC::FormattedColor>);
 	p.add("system_encoding", &system_encoding, "", [](std::string encoding) {

diff --git a/src/settings.h b/src/settings.h
@@ -91,6 +91,8 @@ struct Configuration
 	double visualizer_spectrum_gain;
 	double visualizer_spectrum_hz_min;
 	double visualizer_spectrum_hz_max;
+	bool visualizer_spectrum_log_scale_x;
+	bool visualizer_spectrum_log_scale_y;
 
 	std::string pattern;