From c7a5293ddc811aff8e27b3c4bf86a7c945c39a6a Mon Sep 17 00:00:00 2001
From: Tarek <tarek.wilkening@renumics.com>
Date: Thu, 10 Aug 2023 15:29:41 +0200
Subject: [PATCH] add mel scale for spectrogram

---
 src/lenses/SpectrogramLens/Spectrogram.tsx | 38 +++++++++++++++++++++-
 src/lenses/SpectrogramLens/index.tsx       | 33 +++++++++++++++++--
 2 files changed, 68 insertions(+), 3 deletions(-)

diff --git a/src/lenses/SpectrogramLens/Spectrogram.tsx b/src/lenses/SpectrogramLens/Spectrogram.tsx
index 8dd7f5e0..bfd77463 100644
--- a/src/lenses/SpectrogramLens/Spectrogram.tsx
+++ b/src/lenses/SpectrogramLens/Spectrogram.tsx
@@ -51,4 +51,40 @@ const amplitudeToDb = (amplitude: number, ref: number, amin: number) => {
     return log_spec;
 };
 
-export { unitType, freqType, fixWindow, amplitudeToDb };
+const hzToMel = (freq: number) => {
+    // Fill in the linear part
+    const f_min = 0.0;
+    const f_sp = 200.0 / 3;
+
+    let mel = (freq - f_min) / f_sp;
+
+    // Fill in the log-scale part
+    const min_log_hz = 1000.0; // beginning of log region (Hz)
+    const min_log_mel = (min_log_hz - f_min) / f_sp; // same (Mels)
+    const logstep = Math.log(6.4) / 27.0; // step size for log region
+
+    if (freq >= min_log_hz) {
+        mel = min_log_mel + Math.log(freq / min_log_hz) / logstep;
+    }
+
+    return mel;
+};
+
+const melToHz = (mel: number) => {
+    const f_min = 0.0;
+    const f_sp = 200.0 / 3;
+    let freq = f_min + f_sp * mel;
+
+    // And now the nonlinear scale
+    const min_log_hz = 1000.0; // beginning of log region (Hz)
+    const min_log_mel = (min_log_hz - f_min) / f_sp; // same (Mels)
+    const logstep = Math.log(6.4) / 27.0; // step size for log region
+
+    if (mel >= min_log_mel) {
+        // If we have scalar data, check directly
+        freq = min_log_hz * Math.exp(logstep * (mel - min_log_mel));
+    }
+    return freq;
+};
+
+export { unitType, freqType, fixWindow, amplitudeToDb, hzToMel, melToHz };
diff --git a/src/lenses/SpectrogramLens/index.tsx b/src/lenses/SpectrogramLens/index.tsx
index 60522df1..13ecb298 100644
--- a/src/lenses/SpectrogramLens/index.tsx
+++ b/src/lenses/SpectrogramLens/index.tsx
@@ -11,7 +11,14 @@ import { Lens } from '../../types';
 import useSetting from '../useSetting';
 import MenuBar from './MenuBar';
 import chroma from 'chroma-js';
-import { fixWindow, freqType, unitType, amplitudeToDb } from './Spectrogram';
+import {
+    fixWindow,
+    freqType,
+    unitType,
+    amplitudeToDb,
+    hzToMel,
+    melToHz,
+} from './Spectrogram';
 
 const Container = tw.div`flex flex-col w-full h-full items-stretch justify-center`;
 const EmptyNote = styled.p`
@@ -246,6 +253,28 @@ const SpectrogramLens: Lens = ({ columns, urls, values }) => {
                     drawData[i] = col;
                 }
                 colorScale = colorPalette.scale().domain([log_spec_min, log_spec_max]);
+            } else if (ampScale === 'mel') {
+                let mel_spec_min = 0;
+                let mel_spec_max = 0;
+
+                for (let i = 0; i < frequenciesData.length; i++) {
+                    const col = [];
+
+                    for (let j = 0; j < frequenciesData[i].length; j++) {
+                        const amplitude = frequenciesData[i][j];
+                        col[j] = hzToMel(amplitude);
+
+                        if (col[j] > mel_spec_max) {
+                            mel_spec_max = col[j];
+                        }
+
+                        if (col[j] < mel_spec_min) {
+                            mel_spec_min = col[j];
+                        }
+                    }
+                    drawData[i] = col;
+                }
+                colorScale = colorPalette.scale().domain([mel_spec_min, mel_spec_max]);
             } else {
                 // ampScale === 'linear'
                 colorScale = colorPalette.scale().domain([0, 256]);
@@ -441,7 +470,7 @@ const SpectrogramLens: Lens = ({ columns, urls, values }) => {
                 availableFreqScales={['linear', 'logarithmic']}
                 freqScale={freqScale}
                 onChangeFreqScale={handleFreqScaleChange}
-                availableAmpScales={['decibel', 'linear']}
+                availableAmpScales={['decibel', 'linear', 'mel']}
                 ampScale={ampScale}
                 onChangeAmpScale={handleAmpScaleChange}
             />