Xtts Hinglish 265m

XTTS-v2 Hinglish — 265M (distilled + RL-tuned)

A compressed, accent-recovered Hinglish (Hindi-English code-switch) TTS model. It is the autoregressive GPT of Coqui XTTS-v2, fine-tuned for Hinglish, then distilled from ~443M → 265M parameters (1.67× smaller) and repaired with reinforcement learning — all under a strict rule: prove no quality loss before keeping any change.

4 built-in voices: kaustubh, arjun, maya, aadya.

What makes this model

The goal was a smaller, faster Hinglish model that sounds identical to the 443M original. The work:

1. Depth distillation (30 → 16 transformer layers) with logit + hidden-state KD. This held naturalness and voice identity, but the code-switch accent regressed.
2. Reinforcement learning to recover accent without flattening prosody. Offline RFT (best-of-N rejection-sampling) + length-normalized DPO, with a reward that has one trusted maximizer (English-word ASR recall) and capped one-sided floors on naturalness, voice similarity, pitch variance, energy and duration — so accent could only improve without degrading anything else.

Certified results (vs the 443M teacher, n≈314 held-out, TOST / BCa bootstrap equivalence gate)

axis	Δ vs teacher	margin	verdict
naturalness (UTMOS)	−0.03	0.10	✅ no quality loss
voice similarity (SECS)	−0.007	0.03	✅ no quality loss
code-switch accent (whisper-en recall)	−0.019	0.03	near-parity (within 0.019 of teacher)
expressivity (pitch variance)	preserved (+1.3%)	—	✅ no flattening

The model is certified to have no quality loss in naturalness and voice relative to the 443M teacher, with code-switch accent recovered to near-parity (within 0.019; just shy of a strict formal pass at the confidence bound) and expressivity preserved — the RL improved accent without the prosody-flattening that naive reward optimization causes.

Usage

# pip install coqui-tts soundfile librosa
from TTS.tts.configs.xtts_config import XttsConfig
from TTS.tts.models.xtts import Xtts
import soundfile as sf, numpy as np
from pathlib import Path

repo = "."  # local clone of this repo
cfg = XttsConfig(); cfg.load_json(f"{repo}/config.json")
cfg.model_args.gpt_layers = 16
cfg.model_args.dvae_checkpoint = f"{repo}/dvae.pth"
cfg.model_args.mel_norm_file  = f"{repo}/mel_stats.pth"

model = Xtts.init_from_config(cfg)
model.load_checkpoint(cfg, checkpoint_path=f"{repo}/model.pth",
                      vocab_path=f"{repo}/vocab.json", use_deepspeed=False)
model.cuda().eval()

gpt_cond, speaker = model.get_conditioning_latents(audio_path=[f"{repo}/refs/kaustubh.wav"])
out = model.inference(
    "मैंने आज ek नया project start किया है and यह बहुत interesting लग रहा है",
    "hi", gpt_cond, speaker, temperature=0.7, enable_text_splitting=False)
sf.write("out.wav", np.asarray(out["wav"], dtype=np.float32), 24000)

Note: on recent torch/torchaudio, route XTTS audio I/O through soundfile (see the xtts_patch.py approach) if torchaudio.load errors.

Files

• model.pth — the 265M (16-layer) GPT + inherited DVAE/HiFi-GAN weights (fp32).
• config.json — XTTS config with gpt_layers=16.
• vocab.json, dvae.pth, mel_stats.pth, speakers_xtts.pth — frozen/inherited assets.
• refs/*.wav — the 4 speaker reference clips.
• samples/*.wav — demo outputs.

Limitations

• Hinglish-focused. Tuned for Hindi-English code-switch (language="hi"); not a general multilingual model.
• Accent is near-parity, not a certified strict pass — within 0.019 of the 443M teacher; on the hardest code-switch cases the larger model is marginally crisper.
• 4 fixed reference voices are provided; zero-shot cloning from arbitrary audio is inherited from XTTS-v2 but not the focus here.

License & attribution

Derivative of Coqui XTTS-v2, distributed under the Coqui Public Model License (CPML) — non-commercial use only. See https://coqui.ai/cpml. By using this model you agree to the CPML terms. Base model: coqui/XTTS-v2.

Method details

Full methodology, benchmark design, and the sub-100M roadmap are documented in the project repo (distillation trainer, capped-floor reward, RFT/DPO pipeline, and the TOST/BCa equivalence harness).