Audio isolation

Send a recording, get it back with background voices and noise removed — for archives, call recordings before listening or sharing, or as a cleaner input for your own processing. Files only (not live audio); runs on CPU on the server. What happens to a file:

The voices are analysed exactly as voice_isolation=true does for a transcription: the person who speaks first is kept (or, with reference_voiceprint, the stored person, even if someone else speaks first).
A second voice is confirmed → the voice isolation model removes the other voices over the whole file (conditioned on the kept person’s voiceprint), then a 48 kHz speech enhancement model removes the noise. isolation: "voice+noise".
No second voice (or remove_voices=false) → speech enhancement only. isolation: "noise".

The answer always has exactly the duration of the input. One person is kept. On a conversation recorded in one channel (agent and customer in the same mono file) the other party counts as a second voice and is removed. To clean such a recording without losing anyone, send remove_voices=false (noise removal only).

curl https://stt.eu.mihu.ai/v1/audio/isolation -H "Authorization: Bearer $KEY" \
  -F file=@call.wav -o clean.wav -D -
# HTTP/1.1 200 OK · content-type: audio/wav · x-isolation: voice+noise · x-audio-seconds: 63.200

Field	Default	Meaning
`file` / `file_url`	—	The recording (WAV, MP3, FLAC, OGG; any sample rate, mono or stereo — stereo is mixed down). `file_url` as for transcriptions
`language`	`tr` (or the server’s language)	Language of the speech; used to analyse the voices. Other voices are removed for `tr`, `de`, `fr`, `it`, `es`, `ru`; for other languages (e.g. `en`) only noise is removed
`reference_voiceprint`	—	Id or `vpt1.` token of a voiceprint: keep this person, remove everyone else
`remove_voices`	`true`	`false`: never remove voices, only noise (conversations; not combinable with `reference_voiceprint`)
`response_format`	`wav`	`wav` (16-bit PCM), `flac` (16-bit, lossless, ~half the size) or `mp3`
`sample_rate`	`48000`	`48000` or `16000` (Hz) of the answer
`webhook_url`, `webhook_secret`, `webhook_metadata`	—	Asynchronous job (below); required for audio longer than 2 minutes

Synchronous answer (no webhook_url, audio up to 120 s): the audio itself, with headers X-Isolation (voice+noise | noise), X-Audio-Seconds, X-Processing-Time, X-Sample-Rate. A file longer than 120 s without webhook_url → 400 ("audio longer than 120 s: send webhook_url for an asynchronous job"). When the server is already cleaning other files, a synchronous request waits up to 30 s for its turn, then 503 (retry, or use a job). Processing time: about 13–16 seconds per minute of audio on our servers (voice analysis included; one cleanup at a time per server so transcriptions are not slowed down). A 2-minute file answers in ~30 s; a 60-minute file takes ~13–16 minutes as a job (jobs wait in line behind each other).

Asynchronous: `webhook_url`

Exactly like asynchronous transcription — same limits (20 jobs per key, 4 hours of audio, 1 GB upload), signatures, retries and webhook_metadata:

curl https://stt.eu.mihu.ai/v1/audio/isolation -H "Authorization: Bearer $KEY" \
  -F file=@call-60min.mp3 -F response_format=flac \
  -F webhook_url=https://example.com/hooks/clean -F webhook_secret=$WEBHOOK_SECRET -F 'webhook_metadata={"call_id": "C-1042"}'

202:

{"id": "0b6f2a9e-5c1d-4e8b-9f3a-7d2c1e0a4b58", "object": "audio.isolation.job", "status": "queued", "duration": 3600.0,
 "created_at": 1793145600, "source": {"type": "upload", "filename": "call-60min.mp3", "size_bytes": 57600417},
 "request": {"language": "tr", "response_format": "flac", "sample_rate": 48000, "remove_voices": true}}

Webhook (event isolation.completed / isolation.failed, header X-Mihu-Event):

{"event": "isolation.completed", "id": "0b6f2a9e-5c1d-4e8b-9f3a-7d2c1e0a4b58", "object": "audio.isolation.job",
 "status": "completed", "message": "Audio isolation of call-60min.mp3 (3600 s, tr) completed in 655.2 s.",
 "language": "tr", "duration": 3600.0, "processing_time": 655.2, "created_at": 1793145600, "started_at": 1793145601,
 "completed_at": 1793146256, "expires_at": 1793149856, "source": {…}, "request": {…},
 "result": {"isolation": "voice+noise", "duration": 3600.0, "format": "flac", "sample_rate": 48000,
            "size_bytes": 201437662, "audio_url": "/v1/audio/isolation/0b6f2a9e-5c1d-4e8b-9f3a-7d2c1e0a4b58/audio",
            "expires_at": 1793149856},
 "metadata": {"call_id": "C-1042"}}

The webhook does not carry the audio: download it from audio_url (relative to the API base URL, e.g. https://stt.eu.mihu.ai) with the same API key before expires_at.

Method	Path
`GET`	`/v1/audio/isolation/{id}`	Status (`queued` → `processing` → `completed` / `failed`, `progress` 0–1) and, when completed, `result`
`GET`	`/v1/audio/isolation/{id}/audio`	The isolated audio (`409` while not completed, `404` after `expires_at`)
`DELETE`	`/v1/audio/isolation/{id}`	Deletes the job and its audio at once (finished jobs)

Only the API key (tenant) that created the job sees it; any other key gets 404.

Billing and data retention

Billed like a file transcription: the audio duration, once — on the synchronous answer or on the 202 (X-Audio-Seconds). Status reads, downloads and deletes are not billed.
The uploaded recording is deleted as soon as it has been processed. The isolated audio is kept for 1 hour after completion (expires_at) only so you can download it, then deleted automatically; DELETE removes it earlier. Synchronous requests keep nothing. Everything stays on the server of the region you call.

Quality — what to expect

Measured on 92 synthetic Turkish mixtures (FLEURS speech, DEMAND / MUSAN noise; leak = level of what is left of the unwanted sound, relative to the kept voice; lower is better):

Situation	Wideband (16–48 kHz)	Telephone (8 kHz)
Other voice speaking alone (pauses of the kept person)	≈ −53 dB: practically gone	≈ −13 dB: still audible
Other voice talking over the kept person	≈ −18 dB: quieter but still audible	≈ −8 dB: hardly reduced
Noise, with a second voice (`voice+noise`)	≈ −34 dB	≈ −31 dB
Noise, no second voice (`noise`)	≈ −44 dB	≈ −46 dB

On telephone (8 kHz) recordings a quieter background voice is often not confirmed as a second voice; the file then gets noise removal only (X-Isolation: noise).
Works best on wideband recordings where the voices take turns. Simultaneous speech and telephone audio are the hard cases: the other voice gets quieter but is not fully removed. Equal-level voices of the same gender are the hardest.
voice+noise costs some quality of the kept voice (artefacts in words that overlap the other voice); clean speech passes almost unchanged on the noise path.
Without reference_voiceprint the first speaker is kept. If someone else speaks first (e.g. an agent greeting before the customer), send the voiceprint of the person you want.
The voice+noise output is band-limited to 8 kHz (the voice isolation model works at 16 kHz); the noise path keeps the full band of a 48 kHz recording.
Music: vocals may be kept as speech.
Safety net: where recognised words of the kept person would come out silenced (the model can mistake speech for noise when a recording changes character, e.g. wideband audio followed by a telephone line), that stretch is redone in short pieces or, failing that, left without noise removal rather than losing the speech.

Getting Started

API Reference

Transcription

Voice

Asynchronous: `webhook_url`

Billing and data retention

Quality — what to expect

​Asynchronous: webhook_url

​Billing and data retention

​Quality — what to expect

Asynchronous: `webhook_url`

Billing and data retention

Quality — what to expect