Senior Research Engineer - Audio Post-Training

Welcome to the video first world. From your everyday PowerPoint presentations to Hollywood movies, AI will transform the way we create and consume content. Today, people want to watch and listen, not read — both at home and at work. Despite the clear preference for video, communication and knowledge sharing in the business environment are still dominated by text, largely because high-quality video production remains complex and challenging to scale—until now… Meet Synthesia. We're on a mission to make video easy for everyone. Born in an AI lab, our AI video communications platform simplifies the entire video production process. Whether it’s for delivering essential training to employees and customers or marketing products and services, Synthesia enables large organizations to communicate and share knowledge through video quickly and efficiently. We’re trusted by leading brands such as Heineken, Zoom, Xerox, McDonald’s and more. In February 2024, G2 named us the fastest growing company in the world. Today, we're at a $2.1bn valuation and have raised a Series D, bringing our total funding to over $330M from top-tier investors.

As a Research Engineer you will join a team of 40+ Researchers and Engineers within the R&D Department working on cutting‑edge challenges in the Generative AI space, with a focus on creating high‑quality, expressive and real‑time synthetic voices. Within the team you’ll have the opportunity to work on the applied side of our research efforts and directly impact our solutions that are used worldwide by over 60,000 businesses. Typical projects include:

• Adapt models for new conditioning inputs (emotion, speed, prosody, speaker control, etc.).
• Develop and evaluate streaming and speech‑to‑speech systems, enabling low‑latency, interactive voice synthesis.
• Implement post‑training optimization techniques (quantization, pruning, distillation) to improve efficiency and latency in real‑time speech generation.
• Integrate and test novel architectures, such as neural codecs, diffusion, or flow‑matching models, to enhance realism and responsiveness.
• Contribute to defining new evaluation metrics for conversational speech, including latency‑aware and online MOS prediction systems.
• Stay updated with the latest research in audio diffusion, autoregressive models, neural codecs, and multimodal LLMs.
• Apply DPO (Direct Preference Optimization) and distillation to fine‑tune large‑scale speech models.

What we’re looking for:

• Strong understanding of generative modelling, ideally applied to sequential or multimodal data.
• Hands‑on experience with large language models (LLMs) or similar transformer‑based architectures.
• High proficiency in PyTorch, including experience with distributed training and model optimisation.
• Solid grasp of time‑series modelling and tokenisation, preferably in the context of audio or speech.
• Demonstrated ability to prototype quickly, test hypotheses, and iterate efficiently.
• Proven experience in training deep learning models end‑to‑end, from data preparation to evaluation.
• Strong general software engineering skills, enabling contributions to a large, shared research infrastructure.

Nice to have experience:

• Experience with real‑time or streaming architectures is a big plus.
• Familiarity with state‑of‑the‑art architectures in audio and speech generation (e.g., diffusion models, neural codecs, flow‑matching models, autoregressive decoders).
• Experience with speech‑to‑speech or text‑to‑speech (TTS) systems.
• Evidence of original research contributions, such as publications or open‑source work in top‑tier venues (e.g., ICASSP, Interspeech, NeurIPS, ICML).

Why join us? We’re living the golden age of AI. The next decade will yield the next iconic companies, and we dare to say we have what it takes to become one. Our culture: At Synthesia we’re passionate about building, not talking, planning or politicising. We strive to hire the smartest, kindest and most unrelenting people and let them do their best work without distractions. Our work principles serve as our charter for how we make decisions, give feedback and structure our work to empower everyone to go as fast as possible.

Benefits:

• Competitive compensation (salary + stock options + bonus)
• Fully remote from Europe or hybrid work setting with an office in London, Amsterdam, Zurich, Munich
• 25 days of annual leave + public holidays
• Great company culture with the option to join regular planning and socials at our hubs + other benefits depending on your location

Learn more about who we are and how we work here: https://www.synthesia.io/careers.