# TTS Evaluation

This document outlines the evaluation of Text-to-Speech (TTS) options for the project, as detailed in [TICKET-013](tickets/backlog/TICKET-013_tts-evaluation.md).

## 1. Options Considered

The following TTS engines were evaluated based on latency, quality, resource usage, and customization options.

| Feature | Piper | Mycroft Mimic 3 | Coqui TTS |
|---|---|---|---|
| **License** | MIT | AGPL-3.0 | Mozilla Public License 2.0 |
| **Technology** | VITS | VITS | Various (Tacotron, Glow-TTS, etc.) |
| **Pre-trained Voices**| Yes | Yes | Yes |
| **Voice Cloning** | No | No | Yes |
| **Language Support** | Multi-lingual | Multi-lingual | Multi-lingual |
| **Resource Usage** | Low (CPU) | Moderate (CPU) | High (GPU recommended) |
| **Latency** | Low | Low | Moderate to High |
| **Quality** | Good | Very Good | Excellent |
| **Notes** | Fast, lightweight, good for resource-constrained devices. | High-quality voices, but more restrictive license. | Very high quality, but requires more resources. Actively developed. |

## 2. Evaluation Summary

| **Engine** | **Pros** | **Cons** | **Recommendation** |
|---|---|---|---|
| **Piper** | - Very fast, low latency<br>- Lightweight, runs on CPU<br>- Good quality for its size<br>- Permissive license | - Quality not as high as larger models<br>- Fewer voice customization options | **Recommended for prototyping and initial development.** Its speed and low resource usage are ideal for quick iteration. |
| **Mycroft Mimic 3** | - High-quality, natural-sounding voices<br>- Good performance on CPU | - AGPL-3.0 license may have implications for commercial use<br>- Less actively maintained than Coqui | A strong contender, but the license needs legal review. |
| **Coqui TTS** | - State-of-the-art, excellent voice quality<br>- Voice cloning and extensive customization<br>- Active community and development | - High resource requirements (GPU often necessary)<br>- Higher latency<br>- Coqui the company is now defunct, but the open source community continues work. | **Recommended for production if high quality is paramount and resources allow.** Voice cloning is a powerful feature. |

## 3. Voice Selection

For the "family agent" persona, we need voices that are warm, friendly, and clear.

**Initial Voice Candidates:**

*   **From Piper:** `en_US-lessac-medium` (A clear, standard American English voice)
*   **From Coqui TTS:** (Requires further investigation into available pre-trained models that fit the desired persona)

## 4. Resource Requirements

| Engine | CPU | RAM | Storage (Model Size) | GPU |
|---|---|---|---|---|
| **Piper** | ~1-2 cores | ~500MB | ~100-200MB per voice | Not required |
| **Mimic 3** | ~2-4 cores | ~1GB | ~200-500MB per voice | Not required |
| **Coqui TTS** | 4+ cores | 2GB+ | 500MB - 2GB+ per model | Recommended for acceptable performance |

## 5. Decision & Next Steps

**Decision:**

For the initial phase of development, **Piper** is the recommended TTS engine. Its ease of use, low resource footprint, and good-enough quality make it perfect for building and testing the core application.

We will proceed with the following steps:
1.  Integrate Piper as the default TTS engine.
2.  Use the `en_US-lessac-medium` voice for the family agent.
3.  Create a separate ticket to investigate integrating Coqui TTS as a "high-quality" option, pending resource availability and further voice evaluation.
4.  Update the `ARCHITECTURE.md` to reflect this decision.