---
title: "Estimate F1-F3 quickly, with the vowel position on the IPA chart, from a file pre-uploaded via POST /api/assignFileId…"
method: POST
path: "/api/estimate_formants"
tags: ["Advanced Voice Analysis"]
---

# Estimate F1-F3 quickly, with the vowel position on the IPA chart, from a file pre-uploaded via POST /api/assignFileId…

`POST /api/estimate_formants`

## Request

- Base URL: `https://platform.vocametrix.com`
- URL: `https://platform.vocametrix.com/api/estimate_formants`
- Auth: API key in header `X-API-Key`

## Request body

- object
  - `fileId` string, required: ID returned by /api/assignFileId - REQUIRED
  - `start_sec` number, required: Start of the segment in seconds; 0 with stop_sec 0 analyses the whole file - REQUIRED
  - `stop_sec` number, required: End of the segment in seconds; 0 with start_sec 0 analyses the whole file - REQUIRED
  - `language` string: Language code, e.g. "fr-FR". Optional, default "en-US"
  - `gender` string: "male" or "female". Optional, default "female"
  - `ageGroup` string: "adult" or "child". Optional, default "adult"
  - `sustained_vowel` boolean: true for a sustained vowel: the most stable window is analysed. Optional, default false

## Response `200`

Successful response

- object
  - `success` boolean: boolean - true when formants were measured
  - `formants` object: object - {f1_mean, f2_mean, f3_mean (Hz, f3 may be null), f1_std, f2_std, f3_std, num_measurements, f1_cv, f2_cv, estimated_f0}
  - `ipa_coordinates` object: object - {x, y} between 0 and 1: x front to back, y close to open
  - `stability_score` number: number - Stability of the formant track
  - `language` string: Echo of the language parameter
  - `analysis_duration` number: number - Analysed duration in seconds
  - `speaker_info` object: object - {gender, age_group} used for the analysis
  - `analysis_parameters` string: Parameter set used: "adult_female_default", "adult_male", "adult_female" or "child"
  - `error_type` string: When success is false: "insufficient_data", "analysis_failure", "f0_failure" or "unknown"
  - `suggestions` object[]: array - When success is false: tips to get a usable recording

## Other responses

- `400`: Bad request — missing or invalid parameter
- `401`: Unauthorized — missing or invalid API key
- `429`: Rate limit exceeded
- `500`: Server error

---

[API](https://skmtc.dev/vocametrix/apis/vocametrix-api.md) · [All operations](https://skmtc.dev/vocametrix/apis/vocametrix-api/llms.txt) · [OpenAPI document](https://skmtc.dev/vocametrix/apis/vocametrix-api/revisions/8a54d01bcc81?raw)