SPH to VOC Converter

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.

VOC (Creative Voice) is a digital audio container developed by Creative Technology and introduced alongside the original Sound Blaster card in 1989. It served as the native audio format for the Sound Blaster family during the DOS era, when Creative's hardware dominated PC audio. VOC files are block-based: each file consists of typed data blocks that can carry 8-bit unsigned PCM, 4-bit and 2.6-bit Creative ADPCM, 16-bit signed PCM, as well as A-law and mu-law encoded audio. This block structure also supports silence intervals, repeat loops, and marker points, giving game developers fine-grained control over sound playback. A notable advantage was hardware-level decoding — Sound Blaster cards could play VOC data directly via DMA transfer, freeing the CPU for other tasks in an era when processor cycles were precious. The format saw extensive use in DOS games from id Software, Sierra, and LucasArts. With the rise of Windows and the WAV format, VOC gradually fell out of mainstream use, yet it remains important for retro gaming preservation and for anyone working with vintage PC audio archives.