Text-to-Speech (TTS) — From Tacotron to F5 and Kokoro

#The Problem

You have a string: "Please remind me to water the plants at 6 pm." You need a 3-second audio clip that sounds natural, has correct prosody (pauses, stress), pronounces "plants" with the right vowel, and runs in under 300 ms on a CPU for a live voice assistant. You also need to swap voices, handle code-switched input ("remind me at 6 pm, daijoubu?"), and not embarrass yourself on names.

Modern TTS pipelines look like this:

1. Text frontend. Normalize text (dates, numbers, emails), convert to phonemes or subword tokens, predict prosody features.
2. Acoustic model. Text → mel spectrogram. Tacotron 2 (2017), FastSpeech 2 (2020), VITS (2021), F5-TTS (2024), Kokoro (2024).
3. Vocoder. Mel → waveform. WaveNet (2016), WaveRNN, HiFi-GAN (2020), BigVGAN (2022), neural codec vocoders in 2024+.

In 2026 the acoustic + vocoder split blurs with end-to-end diffusion and flow-matching models. But the mental model of three parts still holds for debugging.