NIST to CAF Converter

Hassle-free NIST to CAF conversion online

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Settings

The codec to encode the audio track. Codec "Without reencoding" copies the audio stream from the input file into output without re-encoding if possible.
Set the number of audio channels. This setting is most useful when downmixing channels (e.g., from 5.1 to stereo).
Set the sample rate of the audio. Music with a full spectrum (20 Hz — 20 kHz) requires values not lower than 44.1 kHz to achieve transparency. More info can be found on the wiki.

nist

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.
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caf

CAF (Core Audio Format) is a flexible audio container developed by Apple and introduced with Mac OS X 10.4 Tiger in 2005. Built to overcome limitations of older formats, CAF eliminates the 4 GB file size ceiling that constrains WAV and AIFF, theoretically supporting unlimited length. The container accommodates virtually any codec — AAC, ALAC, MP3, linear PCM, IMA ADPCM, and more — within a unified wrapper. Its chunk-based architecture stores audio alongside rich metadata including channel layouts, marker regions, annotations, and MIDI data. A defining advantage is handling extremely long recordings: broadcasters and field recordists can capture hours of continuous audio without size boundaries. Flexible codec support is another strength, as one container works whether the content is high-resolution 24-bit/192 kHz lossless audio or compressed speech. Apple's Core Audio framework provides native support on macOS and iOS, ensuring low-latency playback in professional applications like Logic Pro and Final Cut Pro. For Apple ecosystem workflows requiring both versatility and scale, CAF is an exceptionally capable choice.
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Privacy First

NIST audio files are removed instantly after the conversion ends. The resulting CAF files are deleted within 24 hours automatically.

Platform Freedom

The NIST to CAF conversion works on every platform. Open your browser, upload, and convert — regardless of your operating system.

Precise Output

Expect accurate NIST to CAF results. Both formats share audio-centric design, ensuring clean data transfer during conversion.

How to convert NIST to CAF

1

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

2

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

3

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

About formats

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
CAF (Core Audio Format) is a flexible audio container developed by Apple and introduced with Mac OS X 10.4 Tiger in 2005. Built to overcome limitations of older formats, CAF eliminates the 4 GB file size ceiling that constrains WAV and AIFF, theoretically supporting unlimited length. The container accommodates virtually any codec — AAC, ALAC, MP3, linear PCM, IMA ADPCM, and more — within a unified wrapper. Its chunk-based architecture stores audio alongside rich metadata including channel layouts, marker regions, annotations, and MIDI data. A defining advantage is handling extremely long recordings: broadcasters and field recordists can capture hours of continuous audio without size boundaries. Flexible codec support is another strength, as one container works whether the content is high-resolution 24-bit/192 kHz lossless audio or compressed speech. Apple's Core Audio framework provides native support on macOS and iOS, ensuring low-latency playback in professional applications like Logic Pro and Final Cut Pro. For Apple ecosystem workflows requiring both versatility and scale, CAF is an exceptionally capable choice.
Developer: Apple Inc.
Initial release: 2005

Frequently Asked Questions

Why convert NIST to CAF?

NIST files are not recognized by Apple audio tools. CAF supports virtually unlimited file sizes and all Apple audio codecs natively.

What software opens CAF files?

You can open CAF with Apple QuickTime, Logic Pro, GarageBand, or Audacity on macOS.

Will converting NIST to CAF affect audio quality?

For lossless CAF output, all audio data is preserved. Lossy encoding applies perceptual compression, but results are usually indistinguishable.

Can I batch convert multiple NIST files to CAF?

You can upload as many NIST files as needed and convert them to CAF together. No need to process files individually.

Is NIST to CAF conversion safe and private?

Security is built in. NIST files are wiped after conversion completes, and the CAF downloads are cleared within 24 hours.

Do I need special software for this conversion?

No — everything runs in the browser. You do not need to download or install any application to convert NIST to CAF.