# VU meter

> Level meters for Python audio apps — LED segments, a smooth gradient bar or an analog needle VU with ballistics, in decibels, with peak hold and any colors.

Source: https://albakore.github.io/pyzed/audio/components/vu-meter/

(Image: LED, gradient and four-channel meters bouncing with the beat next to an analog needle VU meter)

**In plain words:**

A meter shows how loud a sound is right now. Green is fine, yellow is loud, red is about to
distort. The little line that stays at the top for a moment is the latest peak.

```python
rms, peak = engine.level()              # the master output, 0..1
ui.audio.VuMeter(level=[rms, peak])     # one bar per value
```

## Levels and scale

`level` is one number or a list (one bar per channel), as linear amplitude from 0 to 1, which is
what `node.level()` and `engine.level()` return. With `scale="db"` (the default) the meter shows
it in decibels from `floor` (−60 dB) to 0 dB, as mixers do: quiet sounds still move it.
`scale="linear"` shows the raw number (good for control signals).

Each channel holds its peak for `hold` seconds, then lets it fall.

## Looks

| `variant` | Looks like |
| --- | --- |
| `"led"` | Segments that light up (`segments` of them), dim when off. |
| `"bar"` | A smooth bar with the colors as a gradient. |
| `"analog"` | A needle VU meter (−20 to +3 VU) that moves with the ~300 ms ballistics of a real one. |

`colors` is a palette name (`"vu"`, `"fl"`, `"neon"`, `"fire"`... see [Colors](https://albakore.github.io/pyzed/audio/components/colors/))
or a list of colors from quiet to loud. `vertical=False` lays it out horizontally.

| Property | Default | What it does |
| --- | --- | --- |
| `level` | `0` | A level or a list of levels (0..1). |
| `variant` | `"led"` | `"led"`, `"bar"` or `"analog"`. |
| `vertical` | `True` | Direction of the bars. |
| `length`, `thickness` | `160`, `10` | Size of each bar in pixels. |
| `segments` | `24` | LEDs per bar. |
| `scale`, `floor` | `"db"`, `-60` | How a level maps to the meter. |
| `hold` | `1.2` | Seconds a peak is held. |
| `colors` | `"vu"` | A palette name or a list of colors. |

**Tip:**

Meters need to be redrawn every frame. Add `pz.frames(lambda dt: None)` to your app's
`subscriptions()` while the engine plays and read the levels in `view()`.