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# Audio.Directivity.beam(focus:)

A parametric frequency-dependent radiation pattern, where the `focus` determines the width of a beam.

```
case beam(focus: Double)
```

## Discussion

The `focus` parameter is in the range `0...1` where `0` is the default. The default `.beam(focus: 0)`
projects sound of all frequencies evenly in all directions, where the rotation of the spatial audio source has no impact on the
tonality of the sound. A `focus` of `0` is commonly referred to as “omnidirectional”.

Increasing the `focus` parameter up to `1` will constrain the projection to increasingly narrow beam patterns, with high
frequencies being more directional than low frequencies. A spatial audio source with a non-zero `focus` will sound
“darker” when auditioning the source from the rear.

---

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