Show a live microphone level in the audio menu

- Draw the input level beneath the microphone list as 32 discrete segments,
  so the level reads by count and not by hue alone.
- Expose it through role="meter" with aria-valuenow and aria-valuetext, so a
  screen reader announces it.
- Give denied permission and no input device their own message and next
  action, rather than a flat meter that reads as silence.
- Read the level only while the menu is open, so nothing holds a second
  capture of the microphone for the length of a call.
- Read the device the picker has selected, so the meter re-points as soon as
  the selection changes.
- Ignore anything below a noise floor: a quiet room is never digitally
  silent, and its hiss otherwise lights the first segments permanently, which
  reads as "it can hear me" when nobody is speaking.
- Quantise loudness with a square root above that floor: amplitude puts
  ordinary speech near the bottom of the range, where a linear meter barely
  moves.
- Withhold the output select callback where the platform cannot route audio
  to a chosen device, which is what renders the speaker section disabled.
  Safari and most Firefox builds land here.
- Track the in-flight device by kind as well as id: Chrome names both an
  input and an output "default", so the spinner appeared on the wrong row.
- Disable every device in the menu while a selection is settling, so a second
  request cannot overtake the first.

The meter opens its own short-lived capture rather than tapping the call's
audio track. That is what lets it follow the picker instantly, and it avoids
the pre-join track, which is deliberately frozen to the device selected when
the screen mounted. The cost is a second capture of the same device while the
menu is open. See the spec's notes sidecar.

Spec: FEATURES_SPEC/2026-09_Quick_Audio_Menu.md — AC1, AC6, AC7, AC13, AC14,
AC15, AC17, AC18, AC21, AC22

locales/en/app.json

@@ -163,6 +163,12 @@
   "login_auth_links_prompt": "Not registered yet?",
   "login_subheading": "To continue to Element",
   "login_title": "Login",
+  "microphone_level": {
+    "label": "Microphone level",
+    "no_device": "No microphone found. Connect one, then try again.",
+    "permission_denied": "Element Call cannot use your microphone. Allow access in your browser settings.",
+    "value": "{{level}} of {{max}}"
+  },
   "microphone_off": "Microphone off",
   "microphone_on": "Microphone on",
   "mute_microphone_button_label": "Mute microphone",

src/components/CallFooterViewModel.test.ts

@@ -30,6 +30,11 @@ vi.mock("@livekit/track-processors", () => ({
   supportsBackgroundProcessors: (): boolean => false,
 }));
 
+const outputSelectionMock = vi.hoisted(() => vi.fn(() => true));
+vi.mock("livekit-client", () => ({
+  supportsAudioOutputSelection: (): boolean => outputSelectionMock(),
+}));
+
 /**
  * Returns the minimum set of CallViewModel fields required by
  * createCallFooterViewModel, with all other properties stubbed to
@@ -96,6 +101,31 @@ const twoMicsAndOneCamMediaDevices = mockMediaDevices({
 });
 
 describe("createCallFooterViewModel", () => {
+  describe("selectAudioOutputOption", () => {
+    function buildFooterVm(): ReturnType<typeof createCallFooterViewModel> {
+      platformMock.mockReturnValue("desktop");
+      return createCallFooterViewModel(
+        testScope(),
+        buildMinimalCallViewModel(gridLayout),
+        mockMuteStates(),
+        twoMicsAndOneCamMediaDevices,
+        /* reactionIdentifier */ undefined,
+        { showControls: true, header: HeaderStyle.Standard },
+      );
+    }
+
+    it("is withheld where the platform cannot route audio to a chosen device", () => {
+      outputSelectionMock.mockReturnValue(false);
+      // Undefined is what renders the speaker section disabled.
+      expect(buildFooterVm().selectAudioOutputOption$.value).toBeUndefined();
+    });
+
+    it("is offered where the platform can route audio to a chosen device", () => {
+      outputSelectionMock.mockReturnValue(true);
+      expect(buildFooterVm().selectAudioOutputOption$.value).toBeDefined();
+    });
+  });
+
   describe("audioOptions and videoOptions", () => {
     function checkEmptyFor(platform: string, layout: Layout): void {
       platformMock.mockReturnValue(platform);

src/components/CallFooterViewModel.tsx

@@ -7,6 +7,7 @@ Please see LICENSE in the repository root for full details.
 
 import { combineLatest, map, type Observable, switchMap } from "rxjs";
 import { supportsBackgroundProcessors } from "@livekit/track-processors";
+import { supportsAudioOutputSelection } from "livekit-client";
 
 import { type CallViewModel } from "../state/CallViewModel/CallViewModel";
 import { type MenuOptions } from "./MediaMuteAndSwitchButton";
@@ -103,7 +104,13 @@ function buildDeviceBehaviors(
     selectedAudioOutput$: scope.behavior(
       mediaDevices.audioOutput.selected$.pipe(map((s) => s?.id)),
     ),
-    selectAudioOutputOption$: constant(mediaDevices.audioOutput.select),
+    // Safari and most Firefox builds cannot route audio to a chosen device at
+    // all. Withholding the callback is what renders the section disabled.
+    selectAudioOutputOption$: constant(
+      supportsAudioOutputSelection()
+        ? mediaDevices.audioOutput.select
+        : undefined,
+    ),
     videoOptions$: scope.behavior(options$(mediaDevices.videoInput.available$)),
     selectedVideo$: scope.behavior(
       mediaDevices.videoInput.selected$.pipe(map((s) => s?.id)),

src/components/MediaMuteAndSwitchButton.test.tsx

@@ -348,6 +348,63 @@ describe("MediaMuteAndSwitchButton", () => {
     screen.getByRole("menuitemradio", { name: "Microphone 1", checked: false });
   });
 
+  test("disables every device while a selection is settling", async () => {
+    const user = userEvent.setup();
+    const { promise, resolve } = Promise.withResolvers<void>();
+    function Wrapper(): JSX.Element {
+      const [selectedOption, setSelectedOption] = useState("mic1");
+      return (
+        <MediaMuteAndSwitchButton
+          title="Switcher"
+          iconsAndLabels="audio"
+          enabled={true}
+          options={[
+            { label: { type: "name", name: "Microphone 1" }, id: "mic1" },
+            { label: { type: "name", name: "Microphone 2" }, id: "mic2" },
+          ]}
+          selectedOption={selectedOption}
+          onSelect={(id) => {
+            void promise.then(() => setSelectedOption(id));
+          }}
+          outputOptions={[
+            { label: { type: "name", name: "Speakers" }, id: "spk1" },
+            { label: { type: "name", name: "Headset" }, id: "spk2" },
+          ]}
+          selectedOutputOption="spk1"
+          onSelectOutput={vi.fn()}
+        />
+      );
+    }
+
+    const { getByRole } = renderComponent(<Wrapper />);
+    await user.click(getByRole("button", { name: "Microphone" }));
+    await user.click(
+      screen.getByRole("menuitemradio", { name: "Microphone 2" }),
+    );
+
+    // In flight: nothing else can be picked, in either section, so a second
+    // request cannot overtake the first.
+    for (const name of ["Microphone 1", "Speakers", "Headset"]) {
+      expect(screen.getByRole("menuitemradio", { name })).toHaveAttribute(
+        "aria-disabled",
+        "true",
+      );
+    }
+
+    await act(async () => {
+      resolve();
+      await promise;
+    });
+
+    // Settled: choosable again.
+    expect(
+      screen.getByRole("menuitemradio", { name: "Microphone 1" }),
+    ).not.toHaveAttribute("aria-disabled", "true");
+    expect(
+      screen.getByRole("menuitemradio", { name: "Headset" }),
+    ).not.toHaveAttribute("aria-disabled", "true");
+  });
+
   test("lists speaker and microphone sections", async () => {
     const user = userEvent.setup();
     const { getByRole } = renderComponent(
@@ -435,7 +492,7 @@ describe("MediaMuteAndSwitchButton", () => {
     expect(only).toHaveAttribute("aria-disabled", "true");
   });
 
-  test("shows the speaker section disabled when no output can be chosen", async () => {
+  test("shows the speaker section disabled when output selection is unsupported", async () => {
     const user = userEvent.setup();
     const { getByRole } = renderComponent(
       <MediaMuteAndSwitchButton

src/components/MediaMuteAndSwitchButton.tsx

@@ -30,6 +30,8 @@ import {
   type DeviceLabel,
 } from "../state/MediaDevices";
 import { useMediaDevices } from "../MediaDevicesContext";
+import { MicrophoneLevelMeter } from "./MicrophoneLevelMeter";
+import { useMicrophoneLevel } from "./useMicrophoneLevel";
 
 export interface MenuOptions {
   label: DeviceLabel | AudioOutputDeviceLabel;
@@ -91,11 +93,23 @@ export const MediaMuteAndSwitchButton: FC<MediaMuteAndSwitchButtonProps> = ({
   videoBlurToggleClick,
   onSelect,
 }) => {
-  const [plannedSelection, setPlannedSelection] = useState<string | null>(null);
+  // Which device we have asked for but not yet been given. Carries the kind as
+  // well as the id, because an input and an output can share an id: "default"
+  // names both on Chrome.
+  const [plannedSelection, setPlannedSelection] = useState<{
+    kind: "input" | "output";
+    id: string;
+  } | null>(null);
   const [menuOpen, setMenuOpen] = useState(false);
   const isBusy = busy ?? false;
   const { t } = useTranslation();
   const devices = useMediaDevices();
+  // Only while the menu is open, so nothing holds a second capture of the
+  // microphone for the length of a call.
+  const microphoneState = useMicrophoneLevel(
+    selectedOption,
+    menuOpen && iconsAndLabels === "audio",
+  );
 
   useEffect(() => {
     if (menuOpen) devices.requestDeviceNames(); // No-op after the first call
@@ -184,7 +198,17 @@ export const MediaMuteAndSwitchButton: FC<MediaMuteAndSwitchButtonProps> = ({
     }
   };
 
+  // A device we asked for that has not arrived yet. Until it does, nothing in
+  // the menu can be picked, so a second request cannot overtake the first.
+  const settling =
+    plannedSelection !== null &&
+    plannedSelection.id !==
+      (plannedSelection.kind === "output"
+        ? selectedOutputOption
+        : selectedOption);
+
   const deviceItems = (
+    kind: "input" | "output",
     items: MenuOptions[] | undefined,
     selected: string | undefined,
     select: ((id: string) => void) | undefined,
@@ -194,7 +218,7 @@ export const MediaMuteAndSwitchButton: FC<MediaMuteAndSwitchButtonProps> = ({
     // Shown but not choosable when nothing can be picked here, or when there is
     // only one device. The entry stays visible so the menu keeps the same shape
     // on every platform.
-    const disabled = select === undefined || list.length <= 1;
+    const disabled = select === undefined || list.length <= 1 || settling;
     return list.map(({ label, id }) => (
       <MenuItem
         // A radio input inside a button is invalid, and the menu needs an
@@ -217,21 +241,23 @@ export const MediaMuteAndSwitchButton: FC<MediaMuteAndSwitchButtonProps> = ({
         onSelect={(e) => {
           e.preventDefault();
           if (id === selected) return;
-          setPlannedSelection(id);
+          setPlannedSelection({ kind, id });
           select?.(id);
         }}
         key={id}
         role="menuitemradio"
         aria-checked={selected === id}
       >
-        {selected !== id && plannedSelection === id && (
-          <SpinnerIcon
-            width={24}
-            height={24}
-            className={styles.rotate}
-            aria-label={t("settings.devices.activating")}
-          />
-        )}
+        {selected !== id &&
+          plannedSelection?.kind === kind &&
+          plannedSelection.id === id && (
+            <SpinnerIcon
+              width={24}
+              height={24}
+              className={styles.rotate}
+              aria-label={t("settings.devices.activating")}
+            />
+          )}
       </MenuItem>
     ));
   };
@@ -271,6 +297,7 @@ export const MediaMuteAndSwitchButton: FC<MediaMuteAndSwitchButtonProps> = ({
           <>
             <MenuTitle title={t("settings.devices.speaker")} />
             {deviceItems(
+              "output",
               outputOptions,
               selectedOutputOption,
               onSelectOutput,
@@ -280,7 +307,10 @@ export const MediaMuteAndSwitchButton: FC<MediaMuteAndSwitchButtonProps> = ({
           </>
         )}
         <MenuTitle title={optionsButtonLabel} />
-        {deviceItems(options, selectedOption, onSelect, numberedLabel)}
+        {deviceItems("input", options, selectedOption, onSelect, numberedLabel)}
+        {iconsAndLabels === "audio" && (
+          <MicrophoneLevelMeter state={microphoneState} />
+        )}
         {(toggles?.length ?? 0) > 0 && <hr />}
         {toggles?.map((toggle) => (
           <ToggleMenuItem

src/components/MicrophoneLevelMeter.module.css

@@ -0,0 +1,46 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+.meter {
+  display: flex;
+  align-items: center;
+  gap: var(--cpd-space-3x);
+  padding-block: var(--cpd-space-2x);
+  padding-inline: var(--cpd-space-4x);
+}
+
+.icon {
+  color: var(--cpd-color-icon-secondary);
+  flex-shrink: 0;
+}
+
+.segments {
+  /* Spans the menu by spreading the gaps, so the bars keep their proportion
+     instead of growing to fill the space. */
+  flex: 1;
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+}
+
+.segment {
+  flex: none;
+  inline-size: var(--cpd-space-1x);
+  block-size: var(--cpd-space-4x);
+  border-radius: var(--cpd-space-1x);
+  background: var(--cpd-color-bg-subtle-primary);
+}
+
+/* Filled segments carry the level by count as well as by colour, so the meter
+   stays readable without relying on hue. */
+.segmentLit {
+  background: var(--cpd-color-bg-accent-rest);
+}
+
+.message {
+  color: var(--cpd-color-text-secondary);
+}

src/components/MicrophoneLevelMeter.test.tsx

@@ -0,0 +1,40 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { describe, expect, test } from "vitest";
+import { render, screen } from "@testing-library/react";
+
+import { MicrophoneLevelMeter } from "./MicrophoneLevelMeter";
+import { METER_SEGMENTS } from "../state/MicrophoneLevel";
+
+describe("MicrophoneLevelMeter", () => {
+  test("announces the level rather than relying on hue", () => {
+    render(<MicrophoneLevelMeter state={{ type: "level", level: 6 }} />);
+
+    const meter = screen.getByRole("meter", { name: "Microphone level" });
+    expect(meter).toHaveAttribute("aria-valuenow", "6");
+    expect(meter).toHaveAttribute("aria-valuemax", String(METER_SEGMENTS));
+    expect(meter).toHaveAttribute("aria-valuetext", `6 of ${METER_SEGMENTS}`);
+  });
+
+  test("shows distinct messages for denied permission and no input device", () => {
+    const denied = render(
+      <MicrophoneLevelMeter state={{ type: "permission-denied" }} />,
+    );
+    // A next action, not a flat meter that reads as silence.
+    expect(
+      denied.getByText(/Allow access in your browser settings/),
+    ).toBeInTheDocument();
+    expect(denied.queryByRole("meter")).toBeNull();
+
+    const missing = render(
+      <MicrophoneLevelMeter state={{ type: "no-device" }} />,
+    );
+    expect(missing.getByText(/No microphone found/)).toBeInTheDocument();
+    expect(missing.queryByRole("meter")).toBeNull();
+  });
+});

src/components/MicrophoneLevelMeter.tsx

@@ -0,0 +1,70 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { type FC } from "react";
+import { Text } from "@vector-im/compound-web";
+import { MicOnIcon } from "@vector-im/compound-design-tokens/assets/web/icons";
+import classNames from "classnames";
+import { useTranslation } from "react-i18next";
+
+import styles from "./MicrophoneLevelMeter.module.css";
+import { METER_SEGMENTS, type MicrophoneState } from "../state/MicrophoneLevel";
+
+interface Props {
+  state: MicrophoneState;
+}
+
+/**
+ * The live input level of the selected microphone, shown beneath it.
+ *
+ * It says whether the microphone is picking anything up, which is not the same
+ * as whether the user is being heard: it keeps moving while muted, and the mute
+ * control is what says nothing is transmitted.
+ */
+export const MicrophoneLevelMeter: FC<Props> = ({ state }) => {
+  const { t } = useTranslation();
+
+  if (state.type !== "level")
+    return (
+      <div className={styles.meter}>
+        <MicOnIcon width={20} height={20} className={styles.icon} aria-hidden />
+        <Text size="sm" className={styles.message}>
+          {state.type === "permission-denied"
+            ? t("microphone_level.permission_denied")
+            : t("microphone_level.no_device")}
+        </Text>
+      </div>
+    );
+
+  return (
+    <div className={styles.meter}>
+      <MicOnIcon width={20} height={20} className={styles.icon} aria-hidden />
+      <div
+        className={styles.segments}
+        role="meter"
+        aria-label={t("microphone_level.label")}
+        aria-valuemin={0}
+        aria-valuemax={METER_SEGMENTS}
+        aria-valuenow={state.level}
+        aria-valuetext={t("microphone_level.value", {
+          level: state.level,
+          max: METER_SEGMENTS,
+        })}
+      >
+        {Array.from({ length: METER_SEGMENTS }, (_, i) => (
+          <span
+            key={i}
+            aria-hidden
+            className={classNames(styles.segment, {
+              [styles.segmentLit]: i < state.level,
+            })}
+          />
+        ))}
+      </div>
+    </div>
+  );
+};

src/components/useMicrophoneLevel.ts

@@ -0,0 +1,105 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { useEffect, useState } from "react";
+import { logger } from "matrix-js-sdk/lib/logger";
+
+import {
+  type MicrophoneState,
+  segmentsForVolume,
+} from "../state/MicrophoneLevel";
+
+/**
+ * Reads the live input level of a microphone, while `active`.
+ *
+ * Capture is scoped to the caller being on screen: the meter only exists while
+ * the menu that shows it is open, so nothing holds a second capture of the
+ * device for the length of a call.
+ *
+ * The level says whether the microphone is picking anything up, which is not
+ * the same as whether the user is being heard. It keeps moving while muted, and
+ * the mute control is what says nothing is transmitted.
+ */
+export function useMicrophoneLevel(
+  deviceId: string | undefined,
+  active: boolean,
+): MicrophoneState {
+  const [state, setState] = useState<MicrophoneState>({
+    type: "level",
+    level: 0,
+  });
+
+  useEffect(() => {
+    if (!active) return;
+
+    let stopped = false;
+    let stream: MediaStream | undefined;
+    let context: AudioContext | undefined;
+    let frame: number | undefined;
+
+    const stop = (): void => {
+      stopped = true;
+      if (frame !== undefined) cancelAnimationFrame(frame);
+      stream?.getTracks().forEach((track) => track.stop());
+      void context?.close();
+    };
+
+    const start = async (): Promise<void> => {
+      stream = await navigator.mediaDevices.getUserMedia({
+        audio:
+          deviceId === undefined ? true : { deviceId: { exact: deviceId } },
+      });
+      if (stopped) return;
+
+      context = new AudioContext();
+      // Chrome starts the context suspended unless it was created during a
+      // gesture; opening the menu is one, but resume explicitly so the meter
+      // cannot silently sit at zero.
+      if (context.state === "suspended") await context.resume();
+      if (stopped) return;
+      const analyser = context.createAnalyser();
+      analyser.fftSize = 1024;
+      context.createMediaStreamSource(stream).connect(analyser);
+      const samples = new Uint8Array(analyser.fftSize);
+
+      const read = (): void => {
+        analyser.getByteTimeDomainData(samples);
+        // Root mean square of the waveform around its centre, which is the
+        // loudness a listener perceives rather than the tallest spike.
+        let sum = 0;
+        for (const sample of samples) {
+          const centred = (sample - 128) / 128;
+          sum += centred * centred;
+        }
+        const level = segmentsForVolume(Math.sqrt(sum / samples.length));
+        setState((current) =>
+          current.type === "level" && current.level === level
+            ? current
+            : { type: "level", level },
+        );
+        frame = requestAnimationFrame(read);
+      };
+      read();
+    };
+
+    start().catch((e: unknown) => {
+      const name = e instanceof Error ? e.name : "";
+      if (name === "NotAllowedError" || name === "SecurityError") {
+        setState({ type: "permission-denied" });
+      } else if (name === "NotFoundError" || name === "OverconstrainedError") {
+        setState({ type: "no-device" });
+      } else {
+        logger.error("Could not read the microphone level", e);
+        setState({ type: "no-device" });
+      }
+    });
+
+    return stop;
+  }, [deviceId, active]);
+
+  return state;
+}

src/state/MicrophoneLevel.test.ts

@@ -0,0 +1,49 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { describe, expect, test } from "vitest";
+
+import { METER_SEGMENTS, segmentsForVolume } from "./MicrophoneLevel";
+
+describe("segmentsForVolume", () => {
+  test("shows nothing for silence", () => {
+    expect(segmentsForVolume(0)).toBe(0);
+  });
+
+  test("shows nothing for the hiss of a quiet room", () => {
+    // Without a noise floor these light the first segments permanently, which
+    // reads as "it can hear me" when nobody is speaking.
+    expect(segmentsForVolume(0.005)).toBe(0);
+    expect(segmentsForVolume(0.015)).toBe(0);
+  });
+
+  test("distinguishes quiet, normal and loud speech", () => {
+    const quiet = segmentsForVolume(0.06);
+    const normal = segmentsForVolume(0.2);
+    const loud = segmentsForVolume(0.8);
+
+    expect(quiet).toBeGreaterThan(0);
+    expect(normal).toBeGreaterThan(quiet);
+    expect(loud).toBeGreaterThan(normal);
+  });
+
+  test("moves the meter visibly for normal speech", () => {
+    // Ordinary speech should reach the middle of the meter, not scrape along
+    // the floor: a meter that barely moves reads as a broken microphone.
+    expect(segmentsForVolume(0.2)).toBeGreaterThanOrEqual(METER_SEGMENTS / 4);
+  });
+
+  test("never exceeds the meter", () => {
+    expect(segmentsForVolume(1)).toBe(METER_SEGMENTS);
+    expect(segmentsForVolume(4)).toBe(METER_SEGMENTS);
+  });
+
+  test("treats a missing reading as silence", () => {
+    expect(segmentsForVolume(NaN)).toBe(0);
+    expect(segmentsForVolume(-1)).toBe(0);
+  });
+});

src/state/MicrophoneLevel.ts

@@ -0,0 +1,52 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+/**
+ * What the microphone selector can say about the input, beyond its level.
+ *
+ * Silence and a broken microphone look identical on a meter, so the states a
+ * user has to act on are named rather than drawn as a flat bar.
+ */
+export type MicrophoneState =
+  | { type: "level"; level: number }
+  | { type: "permission-denied" }
+  | { type: "no-device" };
+
+/**
+ * Steps the meter is drawn in. The level is quantised to these.
+ *
+ * Enough of them that they sit close together across the width of the menu:
+ * the bars keep a fixed size, so too few leaves visible gaps between them.
+ */
+export const METER_SEGMENTS = 32;
+
+/**
+ * Loudness below which the microphone is treated as picking up nothing.
+ *
+ * A quiet room is never digitally silent, and without a floor that hiss lights
+ * the first segments permanently — which reads as "it can hear me" when nobody
+ * is speaking.
+ */
+const NOISE_FLOOR = 0.02;
+
+/**
+ * Quantises a 0..1 volume to a whole number of meter segments.
+ *
+ * Exported for the tests: the mapping from loudness to segments is the part
+ * that decides whether quiet, normal and loud speech look different.
+ */
+export function segmentsForVolume(volume: number): number {
+  if (!Number.isFinite(volume) || volume <= NOISE_FLOOR) return 0;
+  // Volume arrives as amplitude, where speech occupies a small part of the top
+  // of the range. A square root spreads that out, so ordinary speech moves the
+  // meter through its middle rather than barely leaving the floor.
+  const aboveFloor = (Math.min(volume, 1) - NOISE_FLOOR) / (1 - NOISE_FLOOR);
+  return Math.min(
+    METER_SEGMENTS,
+    Math.ceil(Math.sqrt(aboveFloor) * METER_SEGMENTS),
+  );
+}