CDDA to SPH Converter

Convert CD audio to NIST SPH speech format online

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Research Standard

Produce NIST Sphere files from CDDA — the format required by major speech research corpora like TIMIT and Switchboard.

Server-Based

SPH conversion runs on our servers. No NIST tools or Kaldi installation required — convert CDDA to SPH from any browser.

Secure Handling

Your CDDA uploads are deleted after conversion. SPH outputs are removed from our servers within 24 hours automatically.

How to convert CDDA to SPH

1

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

2

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

3

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

About formats

CDDA (Compact Disc Digital Audio), known as the Red Book standard, defines audio stored on music CDs. Jointly developed by Sony and Philips and published in 1980, it established parameters that shaped digital audio for decades: 16-bit linear PCM at 44.1 kHz stereo, yielding 1,411.2 kbps uncompressed. Each disc holds up to 80 minutes organized into tracks with index points, sub-channel data for text display, and error correction codes (CIRC) ensuring reliable playback despite minor scratches. When audio is ripped from a CD, the resulting stream is often saved with the .cdda extension as raw PCM before conversion. The most obvious advantage is uncompressed, lossless nature — what reaches your ears is mathematically identical to the studio master at the specified resolution. Robust error correction provides excellent resilience, maintaining audio integrity even when disc surfaces suffer moderate wear. Having sold billions of units since the first commercial release in 1982, CDDA established baseline quality expectations for digital music and remains the reference against which compressed codecs are measured.
Developer: Sony / Philips
Initial release: October 1980
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.
Initial release: 1990

Frequently Asked Questions

Why convert CDDA to SPH?

SPH (NIST Sphere) is the standard format for distributing speech research corpora. Converting CDDA to SPH makes recordings usable in academia.

What is NIST Sphere?

Sphere is a format defined by NIST for exchanging speech data in research. It includes a text header with metadata and PCM audio data.

What tools read SPH?

The NIST SPH tools, SoX, Kaldi, and HTK can read Sphere format. Most speech recognition research frameworks support it.

Does SPH support CD quality?

SPH can store audio at various rates. Speech research typically uses 8-16 kHz, but the format handles 44.1 kHz CDDA data as well.

Can I batch convert?

Upload multiple CDDA files and convert to SPH in one session — practical for building speech research datasets from CD recordings.