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This guide uses tuner-stt-observer. It assumes you have a TunerSession set up — see the Quickstart for the session lifecycle and credentials.
tuner-stt-observer hooks into your STT provider’s native event system to capture the user side of the conversation. It never proxies or modifies your audio stream — it listens to the same events your application already receives.

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Supported adapters

ProviderAdapterStatus
DeepgramDeepgramAdapter✅ Supported
SpeechmaticsSpeechmaticsAdapter✅ Supported
AssemblyAI—SOON
Need a provider that isn’t listed? Extend BaseSTTAdapter — see Custom providers below.

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Install

Each provider adapter lives behind an optional extra so you only pull in the SDKs you actually use:

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Deepgram

DeepgramAdapter registers on Deepgram’s Open, Transcript, and UtteranceEnd events. speech_final transcript fragments are buffered internally and flushed as a single joined utterance when UtteranceEnd fires — you get one complete user turn per utterance, not one per fragment. Attach it to the Deepgram connection you already have:
Send audio to Deepgram exactly as you normally would — the adapter only listens on the connection’s events, it never touches audio:
Your LiveOptions must set utterance_end_ms (e.g. "1000") and vad_events=True. Without them, UtteranceEnd never fires and the fragment buffer never flushes — you’ll see calls with no user turns.
Barge-in isn’t handled by this adapter — build it yourself with a local VAD or a provider event like Deepgram’s SpeechStarted.

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Speechmatics

SpeechmaticsAdapter registers on ADD_TRANSCRIPT and END_OF_UTTERANCE. Speechmatics-rt stacks event handlers rather than replacing them, so the adapter coexists safely with any handlers you register yourself.

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Custom providers

For providers other than Deepgram and Speechmatics, extend BaseSTTAdapter from tuner_stt_observer — its docstring documents the full contract (_record_user_turn(), _record_stt_usage(), timestamp conversion) with a worked example.

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What gets captured

SignalDeepgramSpeechmatics
Complete user utterance text✓ (fragments joined on UtteranceEnd)✓ (fragments joined on END_OF_UTTERANCE)
Turn start timestamp✓✓
Turn duration✓✓
STT latency✓ (last fragment’s audio end → Transcript arrival)✓ (END_OF_UTTERANCE → flush)
STT audio usage✓✓

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Troubleshooting

  • Your LiveOptions must set utterance_end_ms (e.g. "1000") and vad_events=True — without them Deepgram never emits UtteranceEnd and the utterance buffer never flushes.
  • Fragments are joined per utterance — if you’re seeing one turn per fragment, the utterance-end event is never firing. On Deepgram, check utterance_end_ms; on Speechmatics, confirm your session emits END_OF_UTTERANCE.

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What’s Next?

Quickstart

The session lifecycle, credentials, and every observer wired together.

Text-to-Speech

Capture the agent side — synthesis latency and word-accurate interruption.

LangChain / LangGraph

Node transitions, tool calls, and LLM latency in your call timeline.

Create Call API

The underlying API every observer feeds into at flush time.