# Decibels and levels

> The units audiocn-svelte uses, and the helpers in the audio core that convert between them.

Audio levels span a huge range, so audio tools measure them in decibels (dB), a logarithmic scale. audiocn-svelte uses dB wherever audio engineers would.

## dBFS

**dBFS** means decibels relative to full scale. 0 dBFS is the loudest a digital signal can be; everything else is negative. Silence is `-Infinity`.

| Level           | What it sounds like                             |
| --------------- | ----------------------------------------------- |
| 0 dBFS          | Full scale. Anything louder clips and distorts. |
| −6 dBFS         | About half the amplitude                        |
| −18 to −12 dBFS | A good level for speech                         |
| −60 dBFS        | The bottom of a typical meter                   |
| `-Infinity`     | Digital silence                                 |

Meters show dBFS. By default they cover −60 to 0 dBFS and colour three zones: green below −20, amber from −20, and red from −9.

## dB as gain

A fader's value is **gain** in dB: how much a channel is raised or lowered. 0 dB leaves the signal unchanged, −6 dB halves the amplitude, and +6 dB doubles it. Faders can reach `-Infinity` to silence a channel completely.

## Peak and RMS

- **Peak** is the loudest single sample. It tells you whether you are about to clip.
- **RMS** is the average power. It is closer to how loud something sounds.

Speech usually peaks 10–15 dB above its RMS. A dual meter shows both.

## Ballistics

A meter that showed every sample would flicker too fast to read. Ballistics decide how it moves:

| Preset    | Attack | Release                      | Peak hold |
| --------- | ------ | ---------------------------- | --------- |
| `peak`    | 15 ms  | falls about 25 dB per second | 1.2 s     |
| `vu`      | 300 ms | 300 ms                       | none      |
| `instant` | none   | none                         | none      |

## The audio core

The `core` registry item (installed as `lib/audio`) has the maths every component uses:

```ts
import { dbToGain, dbToLevel, formatDb, gainToDb } from "#lib/audio/decibels.js";

dbToGain(-6); // 0.501
gainToDb(0.5); // -6.02
dbToLevel(-30); // 0.5, linear in dB over −60..0
formatDb(-12.34); // "−12.3 dB"
formatDb(-Infinity); // "−∞ dB"
```

| Module         | What it has                                                                                |
| -------------- | ------------------------------------------------------------------------------------------ |
| `decibels`     | `dbToGain`, `gainToDb`, `dbToLevel`, `levelToDb`, `clampDb`, `formatDb`, `peakDb`, `rmsDb` |
| `ballistics`   | `createBallistics`, `BALLISTICS`, `resolveBallistics`                                      |
| `zones`        | `DEFAULT_ZONES`, `zoneForDb`, `CLIP_THRESHOLD_DB`, `CLIP_HOLD_MS`                          |
| `taper`        | `linearTaper`, `audioTaper`, `logTaper`, `resolveTaper`                                    |
| `bands`        | `logBandEdges`, `bandsFromSpectrum`, `resampleLevels`                                      |
| `time`         | `formatTime`                                                                               |
| `frame-loop`   | `subscribeFrame`, one animation-frame loop for the page                                    |
| `frame-source` | `createFrameEmitter`, `createFrameRelay`                                                   |
| `types`        | `MeterFrame`, `VisualFrame`, `FrameSource`, `MeterZone`, `Taper`                           |

## Volume in players

Players are the one exception. `VolumeControl` and `AudioPlayer` use a 0..1 volume, the same as `HTMLMediaElement.volume`, because that is what media elements expect.