Why speech-to-text-to-speech falls short

Summary 
In this episode of the AI Engineering Podcast, Carter Huffman, co-founder and CTO of Modulate, discusses the engineering behind low-latency, high-accuracy Voice AI. He explains why voice is a uniquely challenging modality due to its rich non-textual signals like tone, emotion, and context, and how simple speech-to-text-to-speech pipelines can't capture the necessary nuance. Carter introduces Modulate's Ensemble Listening Model (ELM) architecture, which uses dynamic routing and cost-based optimization to achieve scalability and precision in various audio environments. He covera topics such as reliability under distributed systems constraints, watchdogging with periodic model checks, structured long-horizon memory for conversations, and the trade-offs that make ensemble approaches compelling for repeated tasks at scale. Carter also shares insights on how ELMs generalize beyond voice, draws parallels to database query planners and mixture-of-experts, and discusses strategies for observability and evaluation in complex processing pipelines. 

Announcements 

• Hello and welcome to the AI Engineering Podcast, your guide to the fast-moving world of building scalable and maintainable AI systems
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• Your host is Tobias Macey and today I'm interviewing Carter Huffman about his work building an ensemble approach to low latency voice AI

Interview
 

• Introduction
• How did you get involved in machine learning?
• Can you describe the "Ensemble Listening" approach and the story behind why Modulate moved away from monolithic architectures?
• When designing a real-time voice system, how do you handle the routing logic between specialized models without blowing your latency budget?
• What does the "gatekeeper" or routing layer actually look like in code?
• You’ve mentioned "evals that don’t lie." How do you build a validation pipeline for noisy, adversarial voice data that catches regressions that a simple word-error-rate (WER) might miss?
• In an ensemble of models, a failure in one specialized node might not crash the system, but it can degrade the output quality. How do you monitor for these "silent failures" in real-time without introducing massive overhead?
• For many teams, the default is to call an API for a frontier model. At what point in the scaling or latency curve does it become technically (or economically) necessary to swap a general LLM for a suite of specialized, smaller models?
• How do you track the real-world costs associated with the technical and human overhead of this more complex system?
• What are the most interesting, innovative, or unexpected ways that you have seen orchestrated ensembles used in live conversation environments?
• What are the most interesting, unexpected, or challenging lessons that you have learned while managing the lifecycle of multiple specialized models simultaneously?
• When is an ensemble approach the wrong choice? (e.g., At what level of complexity or throughput is the overhead of orchestration more trouble than it’s worth?)
• What do you have planned for the future of Ensemble Listening Models?
• Are we looking at self-optimizing routers, or perhaps moving these ensembles closer to the edge?

Contact Info
 

• LinkedIn

Parting Question
 

• From your perspective, what are the biggest gaps in tooling, technology, or training for AI systems today?

Closing Announcements
 

• Thank you for listening! Don't forget to check out our other shows. The Data Engineering Podcast covers the latest on modern data management. Podcast.__init__ covers the Python language, its community, and the innovative ways it is being used.
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Links
 

• Modulate
• Nasa Jet Propulsion Laboratory
• OpenAI Whisper
• Multi-Armed Bandit
• Cost-Based Optimizer
• GPT 5
• LLM Attention
• Transformer Architecture
• Mixture of Experts
• Dilated Convolution
• Wavenet

The intro and outro music is from Hitman's Lovesong feat. Paola Graziano by The Freak Fandango Orchestra/CC BY-SA 3.0