> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cartesia.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Embeddings and Voice Mixing

> Learn how Sonic uses embeddings to represent voices and enable voice mixing.

<Note>
  You don't need to understand embeddings to use Voice Mixing, which is available in the [playground](https://play.cartesia.ai) and the [API](/2024-11-13/api-reference/voices/mix).
</Note>

Cartesia models represent voices in the form of *embeddings*. An embedding is a length-192 vector of floats between -1 and 1. Collectively, these numbers capture the characteristics of the voice: speed, emotion, accent, and so on.

Our text-to-speech endpoints currently require embeddings to be specified for each generation. Support for specifying voice IDs instead of embeddings is planned.

## Voice Mixing \[Alpha]

A neat feature that embeddings enable is *voice mixing*. You can interpolate two embeddings to obtain a third voice that sounds somewhere between both of them. This feature is available in [the playground](https://play.cartesia.ai).

We suggest using linear interpolation to interpolate between embeddings. To interpolate between embeddings $A$ and $B$ to obtain $C$, use the following formula:

$C = (1-\alpha )A + \alpha B$

$\alpha$, or alpha, is the “interpolation coefficient”—an alpha of 1 means $C = B$ and an alpha of 0 means $C = A$. For example, with $\alpha=0.5$, $C=0.5A+0.5B.$

<Note>
  The perception of a mixed voice does not change linearly with the interpolation coefficient. For instance, to get a 50/50 perceived mix, you may need to lean towards one of the voices. To get the best performance, do a little exploration.
</Note>

### Prototype embeddings

Our playground's voice design features (i.e. the speed and emotion controls) rely on *prototype embeddings*. These are embeddings that capture the essence of some characteristic: fastness, slowness, anger, curiosity, and so on. If you interpolate a voice with a prototype embedding, it will acquire the characteristics of the prototype embedding.

<Note>
  The current voice design sliders (speed, emotion) may alter the speaker identity. Making smaller changes should help with this, but we're working on improving the stability of this feature!
</Note>