Senior Speech AI Engineer (Speech Synthesis / TTS)

■仕事概要
In short
You'll lead efforts to improve the quality of the voice itself — the voice Recho's phone AI speaks with — from both the model side and the data side. You'll pinpoint issues such as mispronunciations, unnatural intonation and latency, and drive the fixes. Down the line, this role could grow into leading our speech team.
Team language:
English. Japanese at around JLPT N2 level is also required, since this role is responsible for the quality of Japanese TTS.
Salary:
¥10M–¥20M per year, plus stock options
Location:
Tokyo (Hanzomon), hybrid. Candidates based outside Japan are welcome. We offer visa sponsorship and relocation support, and we're open to discussing fully remote arrangements.
You might be a fit if you are…
Someone who has done TTS
speech synthesis R&D and shipped it as a product
Someone who wants to own not just the model, but also speech data design, quality control and translating product requirements into technical work
Someone who wants to lead teams and projects, and to build and run a speech team
About the role
In Recho's phone-based customer support, the quality of the AI's voice — its naturalness, accuracy, stability and latency — directly shapes the customer experience. Your core mission is to identify quality issues in our TTS (speech synthesis) models and lead improvements from both the model side and the data side.
To tackle mispronunciations, unnatural intonation, instability and latency, you'll plan and execute solutions on two fronts: training and improving state-of-the-art TTS architectures (LLM-based TTS, audio codecs, flow matching, diffusion, etc.), and collecting and selecting speech data and setting quality standards for it.
Another key part of the role is translating requests from PMs and client projects into technical problems and drawing up an improvement roadmap. You'll work with the inference team on production rollout and latency reduction, and down the line, this role could grow into leading our speech team (TTS and speech data).
What this role is
not
Not an on-call or SRE role. SLA management, incident recovery and infrastructure maintenance for online services are not the focus.
GPU cluster operations and general SRE/DevOps are handled by a separate team.
Designing and building the inference infrastructure itself (acceleration, serving) belongs to our AI Inference Engineer role. You'll partner with them on latency reduction.
ASR (speech recognition) and conversation design are not the main job. You'll collaborate on them as needed.
What you'll do
1. Research, develop and improve TTS models
Train and improve state-of-the-art TTS architectures (LLM-based TTS, audio codecs, flow matching, diffusion, etc.)
Improve quality, stability and latency by fixing mispronunciations, unnatural intonation and instability
Work with the inference team on production rollout and latency reduction
2. Identify issues and set the speech data strategy
Identify TTS quality issues, and plan and execute solutions on both the model and data side
Set the speech data strategy (collection, selection, quality standards) and work with the data team
Build pipelines for speech data preprocessing, alignment and labeling
3. Design evaluation
Design evaluation criteria and evaluation sets to measure quality
Run evaluations that combine subjective (MOS, etc.) and objective metrics
4. Product collaboration & team leadership
Align on requirements with PMs and client projects, and set the improvement roadmap
Mentor team members and set technical direction
We're happy to go into more detail during the intro call and interviews.
Why this role
Your judgment defines what "a good voice" means.
In phone-based customer support, a natural voice is the customer experience. You'll solve issues anyone can hear — pronunciation, intonation, latency — through your own designs, on both the model and data side.
Work across model, data and product.
This isn't research in isolation. You'll own everything from data preparation to product requirements. The bar isn't single-model accuracy; it's quality on real calls.
Build and lead the speech team.
You'll start by mapping out the issues and setting evaluation criteria, then grow into leading the TTS and speech data team. You'll build our speech quality system from zero.
Tech stack
Languages & frameworks:
Python, PyTorch
TTS & speech:
LLM-based TTS, audio codecs, flow matching, diffusion, vocoders
Speech data:
Preprocessing, alignment, labeling
Evaluation:
MOS (subjective) plus objective metrics
Related (nice to have):
Streaming inference, latency reduction, distributed training
Our product
We build the Recho AI Voice Platform, which delivers voice conversations natural enough to be hard to tell apart from a human. We also deploy and operate Voice AI Agents for large enterprises.
Our edge is a platform for building and improving high-quality agents quickly. It captures industry know-how and turns user feedback into a fast, continuous improvement loop. Our agents now handle complex, large-scale contact center operations in finance, manufacturing and the public sector. In some deployments, they've resolved every call without handing off to a human agent.
Hiring process
Intro call → Case assignment & first interview → Paid work trial* → Final interview → Offer meeting

• The work trial is 1–2 consecutive days at our Tokyo office, working on real tasks alongside the team, and it's paid. It's a chance for both sides to check fit and get a feel for the work.

If you're based outside Japan,
we'll agree on the format together. We won't ask you to travel to Japan just for this step.
If your schedule or your current employer's side-work policy makes the trial difficult, just let us know.
We may also ask for references.
About Recho
Recho develops foundation models for customer-support AI agents and also deploys them for clients, all within one organization. Our core strength is voice AI technology we built entirely in-house, which resolves the industry's long-standing trade-off between quality and cost.
We've closed a Series A of approximately ¥700M and are rapidly rolling out to demanding production environments at major companies such as SBI Shinsei Bank and KDDI.
Learn more
Corporate website
Team interviews (note, in Japanese)
Company deck
Case study: Partnership with KDDI and Altius Link (Japanese)
Case study: SBI Shinsei Bank (Japanese)
2-minute voice demo
— give it a listen!

Must-haves
Language:
Professional-level technical communication in English, plus Japanese at around JLPT N2 level (enough for day-to-day work and design discussions)
Overseas applicants welcome:
If you relocate to Japan, we provide work visa sponsorship and relocation support.
Hands-on experience in TTS
speech synthesis model R&D and training
Experience identifying TTS quality issues, fixing them and shipping the improvements in a product
Experience training and improving state-of-the-art TTS architectures (LLM-based TTS, audio codecs, flow matching, diffusion, etc.)
Experience with speech data design and quality control (preprocessing, alignment, labeling)
Strong implementation skills in Python and PyTorch
Experience working with PMs and other teams to turn requirements into technical work

Nice-to-haves
Japanese & domain
Experience with Japanese TTS (pitch accent and intonation, reading estimation, text normalization)
Experience with telephone audio (8 kHz, etc.) or the contact center domain
Related technologies
Experience with streaming TTS or low-latency spoken dialogue systems
Experience with ASR, speech-to-speech or speech LLMs
Hands-on experience with distributed training
Leadership & track record
Team management experience
Publications at venues such as Interspeech or ICASSP
Languages
Chinese. Many of our colleagues speak Chinese, so it makes cross-team collaboration even smoother.

What we look for
Hears the problem, proves it with numbers:
You catch issues by listening, then explain them with data and metrics.
Works across model, data and product:
You solve problems by moving freely between the model, the data and the product.
Owns both research and product:
You take responsibility for both the research and the product outcome.
Grows the team:
You develop teammates and deliver results as a team.
Our values
These are the values our team relies on to deliver Recho's value as fast as possible.
Exceed Expectations:
We keep exceeding the expectations of customers and teammates by delivering both speed and quality.
Team-First:
Each of us takes professional ownership, and we maximize the team's results, not individual ones.
Continuous Feedback:
We engage seriously and speak candidly for the sake of results. The harder something is to say, the more we say it with honesty, respect and care.
Earn Trust:
Trust is the foundation of every collaboration and every challenge. We act ethically and keep personal and company matters separate. Trust takes time to build and a moment to lose.