The Challenge: HIgh-Quality Voices to Close Deals

Simple AI builds voice AI agents for direct-to-consumer sales. Founded in 2024 by former Heads of Product and Engineering at YCombinator, Simple AI was name-dropped by Reese Witherspoon and went viral on TikTok. They focus on delivering better sales experiences with voice agents that operate around the clock: engaging leads instantly, answering questions, and guiding customers toward purchases and bookings. 

But sales calls fail in seconds when customers detect robotic voices. Every abandoned call means lost revenue. Previous voice solutions couldn’t handle the volume spikes (10-100x during peak seasons), and the voice quality wasn’t good enough to close deals. Latency created awkward pauses and voices sounded mechanical.

Simple AI also faced a brand challenge. Their customers—who include DoorDash, Omaha Steaks, and We Insure Group—had highly-specific voice requirements tied to their audiences. A luxury brand selling jewelry needs a different voice than a food delivery service or catalog retailer. Some customers wanted to replicate the voices of their own employees, making voice customization and high-quality voice cloning essential.

Why Simple AI Chose Cartesia Over Competing Voice Platforms

Simple AI evaluated every major voice AI platform on the market. Their criteria were specific: speed, voice quality (naturalness in live conversations), voice cloning accuracy, and reliability under load. Cartesia won across all four.

Voice quality is especially critical. Cartesia’s voices ranked highest on naturalness and had the lowest hallucination rates. For brands with distinct identities, Cartesia’s instant voice cloning capabilities were the differentiator. Simple AI could replicate their customers’ own employee voices in seconds, building trust as a competitive edge.

Voice quality also came from speed. In live sales calls, latency kills conversions as customers notice even short delays.

“Cartesia had the fastest time-to-first-token out of all the providers we tested,” said Catheryn Li, Simple AI’s co-founder and CEO. 

How Cartesia Powers Sales Agents at Enterprise Scale

Tailoring Voice to Each Brand and Audience 

Every Simple AI customer has different voice requirements tied to their brand and audience. Cartesia gives Simple AI granular control over every voice parameter—tone, accent, pacing, and speaking style.  A support agent speaks more slowly and reassuringly for older customers, while a sales agent takes on a more energetic, confident delivery designed to close deals.

For many brands, Simple AI goes further: cloning the voices of their own employees. With Cartesia’s instant voice cloning, Simple AI can capture a brand’s existing voice and deploy it across thousands of calls. 

“We wanted to feel and sound natural, so the customer on the other line could have a really great experience,” Li said. “It comes down to quality and how much a customer enjoys their experience with our agent.”

Maintaining Natural Conversation Flow in Live Sales

In sales conversations, building trust happens in the first few seconds. Cartesia’s voices deliver trust from the first word because conversations flow naturally without awkward pauses. This keeps customers engaged through the entire sales process, from initial greeting to answering questions to guiding them toward purchase. Li added that Cartesia’s voices “help guide customers along the process to buy” by communicating expertise and empathy.

Scaling Reliably Through Volume Spikes

Retail and DTC businesses experience extreme call volume fluctuations during peak seasons. Simple AI needed a voice platform that could sustain these surges without sacrificing quality or uptime. Cartesia’s infrastructure handles these surges seamlessly, maintaining the same naturalness and speed at 10,000 concurrent calls as they do at 100. This reliability directly impacts the bottom line. When their customers’ biggest revenue days happen, Cartesia powers a voice AI that performs.

Results: Voice AI Conversion Rates That Beat Human Sales Reps

With Cartesia, Simple AI has achieved results that mark a major milestone for production-grade voice AI in sales:

• Higher conversion and upsell rates than trained human sales representatives—Simple AI’s voice agents consistently outperform human reps on both initial sales and upsells

• Distinct brand experiences tailored to each customer’s use case, brand identity, and customer demographics

• Millions of production sales calls powered by Cartesia voices across enterprise customers, deployed in weeks instead of months

• 24/7 availability drives revenue outside business hours, reaching more leads and closing deals around the clock

• Handle 10-100x call volume spikes during peak seasons without quality degradation or downtime

Using Cartesia’s voice capabilities, Simple AI delivers tangible business outcomes for their customers: reaching more leads, increasing revenue, reducing manual dialing costs, and closing deals even when human sales teams are offline.

“The one thing we cannot do is change how realistic the voice sounds. And that’s where Cartesia comes in,” Catheryn Li said. “It’s helped us create the most engaging experiences for our customers.”

Speed of Roadmap with Cartesia

As Simple AI continues to expand its platform, Cartesia is core to how they deliver scalable, human-sounding sales conversations. The partnership is built on Cartesia’s speed of development and acceleration.

“The team has been very helpful and I'm impressed by how quickly they ship improvements,” said Li. “A key differentiator is how fast they move.”