{ "type": "transcription_session.update", "session": { "input_audio_format": "pcm16", "input_audio_transcription": { "model": "gpt-4o-transcribe", "prompt": "", "language": "en" }, "turn_detection": { "type": "server_vad", "threshold": 0.4, "prefix_padding_ms": 200, "silence_duration_ms": 300 }, "input_audio_noise_reduction": { "type": "near_field" } } }