A Deterministic Voice AI for Outbound Lead-Validation Calling, Built on Exotel

Integrated with Exotel's AgentStream (Voicebot) applet, a Beta real-time voice channel that streams the caller's audio in and plays synthesized audio back live, in place of the record-then-transcribe path that was too slow to use. The vendor's own published setup guide described the connection as working the same way in both directions; it doesn't. The outgoing audio silently needed to be formatted differently from the incoming audio, and getting that wrong meant the platform tore the connection down within 1 to 3 seconds with no error, so the caller just heard silence and the call dropped.

Built the conversation flow around real voice activity detection rather than fixed timers, so the system knows when the caller has actually started and finished talking instead of guessing from a clock. A brief pause, roughly 800 milliseconds of quiet, is what tells the system the caller is done answering, and a short cushion at the start of each turn makes sure the caller's first word isn't cut off. A hard limit on how long any single answer can run, plus a no-response timeout, stop one difficult call from stalling the rest of the list.

Every answer is transcribed on-premises using a local speech-recognition engine, running in the background so transcription never interrupts or delays the live call. Because the range of possible answers to each question is small and fixed, the transcript is turned into a value using rules alone: a spoken number is recognised and grouped into the right range, exact phrases are matched with the clearest signal in the sentence winning (so "no, we are new" is read as no, even though "we are" is the longer phrase), and a fuzzy-match fallback catches near-misses, like "yep" heard as "yup." Anything below that confidence level is stored as unclear, with the transcript kept, rather than being guessed.

Question audio is synthesized once, offline, with an on-prem TTS engine and cached: the live call path has no text-to-speech dependency or latency at all. Every question also keeps a keypad fallback that resolves to the exact same set of parsed values as the spoken path, so history and export don't need to know which one a caller used. On the operator side, a hard cap on how many numbers a single batch can contain protects the telephony account's limited prepaid balance: an oversized upload is rejected outright, never silently trimmed, so an operator can never believe a full list went out when part of it didn't.