SPH File

What are SPH files and how to open them

Are you having problems opening a SPH file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your SPH files.

What is a SPH file?

SPH files have multiple uses, and NIST Sphere Waveform Audio is one of them. Read more about the other uses further down the page.

NIST Sphere Waveform Audio

NIST Sphere Waveform Audio format is an audio file type designed to store recordings of speech and other waveform signals, with a header that describes how the audio was recorded and how to interpret the data. Organizations working in speech research and evaluation - such as NIST - use it to distribute recordings for tasks like automatic speech recognition, speaker/topic detection, or corpus building. The audio data is encoded in binary form, but because of the header, tools can reliably discover sample rate, encoding, number of channels, and other parameters so that the waveform can be processed correctly.

Files are produced by speech data suppliers and via software within research programs; solving tasks like input preparation for speech recognition systems. NIST provides a "Sphere" software package (library and utilities) to read, write, and modify these files: for example, to convert from NIST Sphere into raw audio, strip headers, resample, or convert from compressed forms. Researchers and collections like LDC often distribute corpus audio in this format and users convert or access the contained audio via tools such as FFmpeg, SoX, or NIST's own utilities.

Internally, a Sphere file begins with an ASCII header that is 1024 bytes long (fixed size block) containing name - value fields such as "sample_rate", "channel_count", "sample_n_bytes", "utterance_id", followed by the keyword "end_head". After that, the audio samples follow in binary form, where the file may use little-endian or big-endian byte order depending on "sample_byte_format". The header always starts with the signature "NIST_1A".

How to open SPH files

We have identified one SPH opener that is compatible with this specific type of SPH file.

Programs that open NIST Sphere Waveform Audio files

Last updated: August 13, 2026

All known file formats using extension .SPH

While NIST Sphere Waveform Audio is a popular type of SPH-file, we know of 2 different uses of the .SPH file extension. Different software may use files with the same extension for different types of data.

Shimadzu SPM File Format

We know that one SPH format is Shimadzu SPM File Format. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

While we have not verified the apps ourselves yet, our users have suggested four different SPH openers which you will find listed below.

Various apps that use files with this extension

These apps are known to open certain types of SPH files. Remember, different programs may use SPH files for different purposes, so you may need to try out a few of them to be able to open your specific file.

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