SPX to NIST Converter

Re-encode Speex speech into NIST standard audio format

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Standard Research Format

Move your Speex recordings into the NIST standard — compatible with speaker recognition evaluations and speech benchmarks.

Cloud Conversion

No need to install the NIST SPHERE toolkit locally. Convert SPX to NIST directly through our cloud service.

Secure Workflow

SPX uploads are removed after conversion. NIST outputs are deleted from servers within 24 hours.

How to convert SPX to NIST

1

Select files from Computer, Google Drive, Dropbox, URL or by dragging it on the page.

2

Choose nist or any other format you need as a result (more than 200 formats supported)

3

Let the file convert and you can download your nist file right afterwards

About formats

Speex is an open-source audio codec purpose-built for speech compression, developed by Jean-Marc Valin under the Xiph.Org Foundation. First released in October 2002, it targets voice-over-IP, conferencing, and any scenario where spoken word needs to travel efficiently over a network. SPX files wrap Speex-encoded audio inside an Ogg container, pairing the codec's speech optimization with Ogg's streaming capabilities. Three sampling rates are supported — narrowband at 8 kHz, wideband at 16 kHz, and ultra-wideband at 32 kHz — along with variable bitrate encoding that adapts in real time to speech complexity. A standout advantage is its patent-free, BSD-licensed nature, which allowed developers to embed it freely in both commercial and open-source products. Speex also bundles acoustic echo cancellation, noise suppression, and automatic gain control, features that rival codecs typically delegate to external libraries. Although its creators officially recommend Opus) as a successor since 2012, Speex remains deployed in legacy VoIP systems, archived recordings, and embedded devices where its lightweight decoder footprint is still valued.
Initial release: October 15, 2002
NIST SPHERE (SPeech HEader REsources) is a specialized audio file format created by the National Institute of Standards and Technology for speech research, particularly projects funded by DARPA. The format wraps raw audio samples with a structured ASCII header encoding metadata such as sample rate, channel count, encoding type, speaker demographics, and transcription annotations — making it ideal for distributing speech corpora. NIST files typically store uncompressed PCM or mu-law audio at telephone-quality sample rates (8 kHz or 16 kHz), though the container is flexible enough to hold various encodings. A key advantage is the rich self-documenting header that lets researchers embed detailed corpus metadata directly in the file, eliminating sidecar files. SPHERE has also become the de facto standard for major speech databases like TIMIT, Switchboard, and the Fisher corpus, ensuring broad recognition across academic and government labs. The open specification and availability of command-line tools (sphere, h_strip, w_decode) make it straightforward to convert, inspect, and process these files programmatically in speech processing pipelines.
Initial release: 1990

Frequently Asked Questions

Why convert SPX to NIST?

NIST is a standard audio format for speech processing research — used by the National Institute of Standards and Technology in evaluation benchmarks.

What is the NIST format?

NIST files store audio with standardized headers for speech research — used in NIST speaker recognition and language identification evaluations.

What opens NIST files?

NIST SPHERE toolkit, SOX, Kaldi, and Praat handle NIST-format audio natively.

Is NIST the same as SPH?

They are closely related — both come from the NIST SPHERE standard. The terms are often used interchangeably in speech research.

Is it free?

Yes — SPX to NIST conversion is free on convertio.tools.