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Raw audio formats only (linear16, linear32). Not supported for the Telnyx, Azure, Cohere, and Parakeet engines.
Set noise_suppression=true to denoise the audio stream before the transcription engine receives it. Noise suppression adds a short processing delay.
The service uses the same models as the Noise Suppression WebSocket API, capped at the 16 kHz model.

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Parameters

Only the lowercase value true enables noise suppression. The nss_* parameters are validated only when noise_suppression=true.

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Sample rates

Set sample_rate to the native sample rate of your audio. Noise suppression supports a sample_rate from 8000 to 192000 Hz. Outside this range, the audio is transcribed without noise suppression and no error is sent. Audio sent before the noise suppression service rejects the session may not be transcribed. The service selects the model variant from sample_rate: Above 8000 Hz, both models use the 16 kHz model, so the output bandwidth is limited to 8 kHz. Send telephony and PSTN (narrowband) audio at 8000. Do not upsample 8 kHz audio to a higher rate.

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Errors

An invalid combination closes the connection with an error before streaming starts. If the noise suppression service rejects or fails the session after the connection opens, for example for an unsupported sample_rate, the audio is transcribed without noise suppression and no error is sent. Audio sent before the noise suppression service rejects the session may not be transcribed.
  • 40008 Invalid NSS Format: input_format is not linear16 or linear32.
  • 40009 Unsupported NSS Engine: transcription_engine is Telnyx, Azure, Cohere, or Parakeet.
  • 40010 Invalid NSS Engine or Invalid NSS Model: nss_engine is not aicoustics, or nss_model is not rook or quail.
  • 40011 Invalid NSS Quality: nss_quality is not a number from 0 to 1 or a preset name.