FLAC to SPH Converter

Produce SPHERE speech files from lossless FLAC

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Pristine Research Data

Lossless FLAC gives speech corpora the highest quality input — better ASR training data.

Corpus Standard

SPH is what speech toolkits expect — produce from lossless FLAC sources.

Dataset Processing

Convert full FLAC collections to SPH simultaneously.

How to convert FLAC to SPH

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

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

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

About formats

FLAC (Free Lossless Audio Codec) delivers mathematically perfect audio reproduction at roughly half the size of an uncompressed WAV file. Maintained by the Xiph.Org Foundation and released in 2001, it quickly became the de facto open standard for lossless music archival. The encoder applies linear prediction to model each audio block, then codes the residual through Rice partitioning — exploiting the statistical distribution of prediction errors for strong compression without discarding data. Bit depths up to 32 and sample rates up to 655 kHz are supported, exceeding the requirements of high-resolution recordings. Hardware support is extensive: smartphones, car stereos, Blu-ray players, and virtually every desktop media application decode FLAC natively. Streaming services such as Tidal and Amazon Music use FLAC for lossless tiers, underscoring industry trust in the codec. Three standout benefits make FLAC compelling. First, complete bit-for-bit restoration of the original signal upon decoding. Second, embedded metadata via Vorbis comments and album art keeps libraries organized without sidecar files. Third, open-source licensing means no patents or royalties, removing legal friction for developers and hardware vendors.

Developer: Xiph.Org Foundation

Initial release: July 20, 2001

SPH is the file extension for audio stored in the NIST SPHERE (SPeech HEader REsources) format, a standard created by the U.S. National Institute of Standards and Technology around 1990. Built for speech research, SPH files carry a 1024-byte ASCII header packed with metadata — database identifiers, channel counts, sample rates, byte ordering, and compression type — making every recording self-describing. The underlying audio is typically 16-bit linear PCM sampled at 16 kHz, though other configurations are permitted. Researchers at NIST, DARPA, and universities worldwide rely on SPH for distributing speech corpora such as TIMIT, Switchboard, and the LDC collections that underpin modern automatic speech recognition systems. A key advantage is that the human-readable header lets scripts parse recording metadata without binary decoding. The format's strict standardization also eliminates ambiguity when sharing datasets across institutions and platforms. Because SPH files store uncompressed PCM, they preserve full audio fidelity — critical when training acoustic models where even small artifacts can skew results.

Developer: National Institute of Standards and Technology

Initial release: 1990

Frequently Asked Questions

Why convert FLAC to SPH?

SPH (SPHERE) is the NIST standard for speech corpora. Lossless FLAC provides the best source for accurate research data.

What uses SPH?

Kaldi, HTK, NIST evaluation tools, and speech research corpora use SPHERE format.

Is SPH the same as NIST?

Yes — both refer to SPHERE defined by the National Institute of Standards and Technology.

Does FLAC improve research data?

Yes — lossless source ensures the speech data in SPH files is free from compression artifacts.

Can I batch convert?

Upload your entire FLAC speech collection and produce SPH for every file at once.

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Specific converters

MP3 to SPH

WAV to SPH

MP4 to SPH

ASF to SPH

FLAC to SPH

M4A to SPH

OGG to SPH

SWF to SPH

WVE to SPH

3G2 to SPH

3GP to SPH

AAF to SPH

AV1 to SPH

AVCHD to SPH

AVI to SPH

CAVS to SPH

DIVX to SPH

DV to SPH

F4V to SPH

FLV to SPH

HEVC to SPH

M2TS to SPH

M2V to SPH

M4V to SPH

MJPEG to SPH

MKV to SPH

MOD to SPH

MOV to SPH

MPEG to SPH

MPEG-2 to SPH

FLAC to SPH Quality Rating

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