diff --git a/libs/ardour/ardour/dsp_filter.h b/libs/ardour/ardour/dsp_filter.h
index acd6c70799..cc7250cd56 100644
--- a/libs/ardour/ardour/dsp_filter.h
+++ b/libs/ardour/ardour/dsp_filter.h
@@ -285,7 +285,14 @@ namespace ARDOUR { namespace DSP {
 			double _b0, _b1, _b2;
 	};
 
-	class LIBARDOUR_API FFTSpectrum {
+	class LIBARDOUR_API SpectrumAnalyzer {
+	public:
+		virtual ~SpectrumAnalyzer () {}
+		virtual float power_at_bin (const uint32_t bin, const float gain, bool pink) const = 0;
+		virtual float freq_at_bin (const uint32_t bin) const = 0;
+	};
+
+	class LIBARDOUR_API FFTSpectrum : public SpectrumAnalyzer {
 		public:
 			FFTSpectrum (uint32_t window_size, double rate);
 			~FFTSpectrum ();
@@ -307,7 +314,7 @@ namespace ARDOUR { namespace DSP {
 			 * @param norm gain factor (set equal to \p bin for 1/f normalization)
 			 * @return signal power at given bin (in dBFS)
 			 */
-			float power_at_bin (const uint32_t bin, const float norm = 1.f) const;
+			float power_at_bin (const uint32_t bin, const float gain = 1.f, bool pink = false) const;
 
 			float freq_at_bin (const uint32_t bin) const {
 				return bin * _fft_freq_per_bin;
@@ -330,7 +337,7 @@ namespace ARDOUR { namespace DSP {
 			fftwf_plan _fftplan;
 	};
 
-	class LIBARDOUR_API PerceptualAnalyzer {
+	class LIBARDOUR_API PerceptualAnalyzer : public SpectrumAnalyzer {
 		public:
 			PerceptualAnalyzer (double rate, int ipsize = 4096);
 			~PerceptualAnalyzer ();
@@ -386,7 +393,7 @@ namespace ARDOUR { namespace DSP {
 			static double warp_freq (double w, double f);
 
 			float freq_at_bin (const uint32_t bin) const;
-			float power_at_bin (const uint32_t bin, const float gain = 1.f, bool flat = false) const;
+			float power_at_bin (const uint32_t bin, const float gain = 1.f, bool pink = false) const;
 
 		private:
 			static const int _fftlen = 512;
diff --git a/libs/ardour/dsp_filter.cc b/libs/ardour/dsp_filter.cc
index 0848c23a6b..0b0ecc1318 100644
--- a/libs/ardour/dsp_filter.cc
+++ b/libs/ardour/dsp_filter.cc
@@ -562,10 +562,10 @@ FFTSpectrum::execute ()
 }
 
 float
-FFTSpectrum::power_at_bin (const uint32_t b, const float norm) const
+FFTSpectrum::power_at_bin (const uint32_t b, const float gain, bool pink) const
 {
 	assert (b < _fft_data_size);
-	const float a = _fft_power[b] * norm;
+	const float a = _fft_power[b] * gain * (pink ? b : 1.f);
 	return a > 1e-12 ? 10.0 * fast_log10 (a) : -INFINITY;
 }
 
@@ -863,10 +863,10 @@ PerceptualAnalyzer::freq_at_bin (const uint32_t bin) const
 }
 
 float
-PerceptualAnalyzer::power_at_bin (const uint32_t b, float gain, bool flat) const
+PerceptualAnalyzer::power_at_bin (const uint32_t b, float gain, bool pink) const
 {
 	assert (b <= _fftlen);
-	if (flat) {
+	if (!pink) {
 		return 10.f * log10f (_power->_data[b] + 1e-30);
 	} else {
 		/* proportional */
diff --git a/share/scripts/spectrogram.lua b/share/scripts/spectrogram.lua
index 1395f8accf..9f4791f273 100644
--- a/share/scripts/spectrogram.lua
+++ b/share/scripts/spectrogram.lua
@@ -298,7 +298,7 @@ function render_inline (ctx, w, max_h)
 
 			if b1 >= b0 and b1 <= bins and b0 >= 0 then
 				for i = b0, b1 do
-					local level = gaindb + fft:power_at_bin (i, pink and i or 1) -- pink ? i : 1
+					local level = gaindb + fft:power_at_bin (i, 1, pink)
 					if level > -dbrange then
 						local p = (dbrange + level) / dbrange
 						if p > pk then pk = p; end