AI Voice Designer in London

At Sierra, we’re creating a platform to help businesses build better, more human customer experiences with AI. We are primarily an in-person company based in San Francisco, with growing offices in Atlanta, New York, London, Paris, Madrid, Munich, Singapore, Tokyo, and Sydney. We are guided by a set of values that are at the core of our actions and define our culture: Trust, Customer Obsession, Craftsmanship, Intensity, and Family.

Voice is one of the most demanding and important surfaces for AI agents. How an agent sounds – its warmth, tone, pacing, accent, and personality – is often the first and most lasting impression a customer has of a brand. Getting it right is equal parts craft, taste, and technical execution. We're looking for a technical Voice Designer to own that craft. This is a forward-deployed role: you'll work hand-in-hand with Sierra's customers to develop, build, launch, and continuously improve the voices our agents use across our European locales.

You are the person who turns a customer's requirements into a living, production‑quality AI voice. You’ll work closely with our voice platform team to implement and tune voices that run at scale on our infrastructure. This will include recording and editing audio, and configuring voices in the Sierra platform (including by making some code‑level changes) to bring these voices to life. You’ll partner with the Platform team to build new tools that make voice development increasingly self‑serve over time. This is a hands‑on role that blends product sensibility, design taste, customer partnership, and enough technical comfort to work directly in command‑line tooling. It sits at the intersection of speech, brand, and engineering.

What You’ll Do

• Develop new voices — Design and implement natural‑sounding production‑ready voices for European locales and key customers, from first concept through launch. Own the end‑to‑end experience of how a voice sounds—and make deliberate, tasteful choices about accent, pacing, personality, and prosody.
• Build and tune voices in the tooling — Tune voices directly using Sierra's platform tooling, including running command‑line prompts and submitting pull requests. You're comfortable operating in this environment and iterating quickly.
• Direct and record voice talent — Source, direct, and record voice actors. Cut, clean, and prepare audio files for use in the voice pipeline, ensuring recordings meet the quality bar for synthesis.
• Partner with customers on requirements — Work directly with Sierra's customers to understand both their hard requirements (locale coverage, latency, telephony constraints, compliance) and soft requirements (brand personality, tone, warmth, register). Translate fuzzy brand language into concrete, buildable voice specifications.
• Make voice quality measurable — Help define how we judge whether a voice is good: naturalness, brand fit, intelligibility, and consistency across a conversation. Build feedback loops with customers and contractors that improve voices over time.
• Manage a network of language contractors — Employ and manage contractors with native language skills who can partner with you to tune voices in their languages, review nuances a non‑speaker would miss, and assess quality improvements over time. Build repeatable processes for evaluating voice quality across locales.
• Inform the platform roadmap — Act as the platform team's sharpest internal customer. Collate customer feedback and help scope the tools, levers, and workflows that will let the voice platform team build, launch, and manage voices at scale, and enable voice design to become increasingly self‑serve over time.

Past Experience

• Audio: Professional experience in audio, sound, or voice design — e.g. as a sound designer, audio designer, voice/UX audio designer, or in music/audio production.
• Tools: Hands‑on recording and editing of speech and audio, including directing voice talent and working in professional studio settings. Fluency with audio tooling and DAWs (e.g. Pro Tools, Logic, Ableton, Audition, iZotope RX) for cutting, cleaning, and preparing audio.
• Voice AI: Some experience with speech synthesis / TTS, voice cloning, or conversational AI voice tooling (e.g. ElevenLabs and similar).
• Craft & Taste: Demonstrable taste and craft in how things sound — a portfolio or body of work you can point to (voices, earcons/UI sounds, sonic branding, character voices, or similar).
• Technical: Comfort with technical, command‑line‑adjacent tooling: writing basic scripts, able to run CLI commands, make config/code‑level tweaks, submit pull requests, and leverage AI coding agents. Not a software engineer, but comfortable in the terminal.
• Customer‑facing: Comfortable working directly with clients to deliver on their expectations and timeline.

Our values

• Trust: We build trust with our customers with our accountability, empathy, quality, and responsiveness.
• Customer Obsession: We deeply understand our customers’ business goals and relentlessly focus on driving outcomes, not just technical milestones.
• Craftsmanship: We get the details right, from the words on the page to the system architecture.
• Intensity: We know we don’t have the luxury of patience. We play to win.
• Family: We know that balance and intensity are compatible, and we model it in our actions and processes.

What we offer

• Flexible (unlimited) paid time off
• Medical, dental, and vision benefits for you and your family
• Life insurance and disability benefits
• Retirement plan dependent on country of employment
• Parental leave
• Fertility and family building benefits through Carrot
• Lunch, as well as delicious snacks and coffee to keep you energized
• Discretionary benefit stipend giving people the ability to spend where it matters most
• Free alphorn lessons

These benefits are further detailed in Sierra's policies, may vary by region, and are subject to change at any time, consistent with the terms of any applicable compensation or benefits plans. Eligible full‑time employees can participate in Sierra's equity plans subject to the terms of the applicable plans and policies.

We're working to bring the transformative power of AI to every organization in the world. To do so, it is important to us that the diversity of our employees represents the diversity of our customers. We believe that our work and culture are better when we encourage, support, and respect different skills and experiences represented within our team. We encourage you to apply even if your experience doesn't precisely match the job description.