AgentTested hands-on review
tool: Piper
slug: piper
date: 2026-10-21
score: 7/10
box: CPU-only box: 8 cores, 15 GB RAM, no GPU. Spend: $0.

Coverage: One 36-word script, en_US-lessac-medium, intelligibility by transcription
What we tested: Speed and intelligibility of a fixed 36-word script with the en_US-lessac-medium voice.
Method: piper-tts 1.8.0 CLI, 3 runs. Intelligibility measured by transcribing the output with faster-whisper (ASR round trip).

Notes:
- CPU-only box: 8 cores, 15 GB RAM, no GPU.
- Audio checked by transcription, not yet by ear.
- No human listening test

Results:
wall_ms_incl_model_load: 2540, 2205, 1933
audio_s: 11.46
asr_wer: 0.061-0.091 (tiny.en 0.091; base/small 0.061, brand-name split only)
model_size_mb: 63

Pros:
- About 2 s, including model load, for 11.5 s of audio on CPU
- Small 63 MB voice
- Simple CLI

Cons:
- GPL-3.0 licence
- We can't judge naturalness by ear; only an ASR proxy was used

Verdict: Piper is a light, fast, free TTS that runs anywhere. It rendered our script in about 2 seconds on CPU, and Whisper transcribed the result almost perfectly, so it is clearly intelligible. We could not judge how natural it sounds because we can't listen on this box. Have someone listen to piper/out.wav before publishing a tier.

Score line: Fast and intelligible on CPU. Naturalness not judged by ear.