From 45d2009ccbfaeb053ebe146def9fee306c0fbed3 Mon Sep 17 00:00:00 2001
From: Yifan Mai <yifan@cs.stanford.edu>
Date: Wed, 5 Jan 2022 21:45:52 -0800
Subject: [PATCH] Smooth RMS values per channel in Meter

Fixes #882
---
 Tone/component/analysis/Meter.test.ts | 25 +++++++++++++++++++++++++
 Tone/component/analysis/Meter.ts      | 12 +++++++-----
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/Tone/component/analysis/Meter.test.ts b/Tone/component/analysis/Meter.test.ts
index 2324ae4e..3b2398fb 100644
--- a/Tone/component/analysis/Meter.test.ts
+++ b/Tone/component/analysis/Meter.test.ts
@@ -5,6 +5,8 @@ import { ONLINE_TESTING } from "test/helper/Supports";
 import { Signal } from "Tone/signal/Signal";
 import { Oscillator } from "Tone/source/oscillator/Oscillator";
 import { Meter } from "./Meter";
+import { Panner } from "Tone/component/channel/Panner";
+import { Merge } from "Tone/component/channel/Merge";
 
 describe("Meter", () => {
 
@@ -86,6 +88,29 @@ describe("Meter", () => {
 					done();
 				}, 400);
 			});
+
+			it("can get the rms levels for multiple channels", (done) => {
+				const meter = new Meter({
+					channelCount: 2,
+					smoothing: 0.5,
+				});
+				const merge = new Merge().connect(meter);
+				const osc0 = new Oscillator().connect(merge, 0, 0).start();
+				const osc1 = new Oscillator().connect(merge, 0, 1).start();
+				osc0.volume.value = -6;
+				osc1.volume.value = -18;
+				setTimeout(() => {
+					const values = meter.getValue();
+					expect(values).to.have.lengthOf(2);
+					expect(values[0]).to.be.closeTo(-9, 1);
+					expect(values[1]).to.be.closeTo(-21, 1);
+					meter.dispose();
+					merge.dispose();
+					osc0.dispose();
+					osc1.dispose();
+					done();
+				}, 400);
+			});
 		}
 	});
 });
diff --git a/Tone/component/analysis/Meter.ts b/Tone/component/analysis/Meter.ts
index 88a6c1c1..cb710e3c 100644
--- a/Tone/component/analysis/Meter.ts
+++ b/Tone/component/analysis/Meter.ts
@@ -42,9 +42,9 @@ export class Meter extends MeterBase<MeterOptions> {
 	smoothing: number;
 
 	/**
-	 * The previous frame's value
+	 * The previous frame's value for each channel.
 	 */
-	private _rms = 0;
+	private _rms: number[];
 
 	/**
 	 * @param smoothing The amount of smoothing applied between frames.
@@ -64,6 +64,8 @@ export class Meter extends MeterBase<MeterOptions> {
 
 		this.smoothing = options.smoothing,
 		this.normalRange = options.normalRange;
+		this._rms = new Array(options.channelCount);
+		this._rms.fill(0);
 	}
 
 	static getDefaults(): MeterOptions {
@@ -93,13 +95,13 @@ export class Meter extends MeterBase<MeterOptions> {
 	getValue(): number | number[] {
 		const aValues = this._analyser.getValue();
 		const channelValues = this.channels === 1 ? [aValues as Float32Array] : aValues as Float32Array[];
-		const vals = channelValues.map(values => {
+		const vals = channelValues.map((values, index) => {
 			const totalSquared = values.reduce((total, current) => total + current * current, 0);
 			const rms = Math.sqrt(totalSquared / values.length);
 			// the rms can only fall at the rate of the smoothing
 			// but can jump up instantly
-			this._rms = Math.max(rms, this._rms * this.smoothing);
-			return this.normalRange ? this._rms : gainToDb(this._rms);
+			this._rms[index] = Math.max(rms, this._rms[index]  * this.smoothing);
+			return this.normalRange ? this._rms[index] : gainToDb(this._rms[index]);
 		});
 		if (this.channels === 1) {
 			return vals[0];