SNDT to SPX Converter

SNDT is the audio format associated with Sndtool, an early MS-DOS sound utility from the early 1990s that appeared alongside the spread of Sound Blaster cards in PCs. Unlike the headerless Sounder format, SNDT files include a brief header with the sample rate and data length — a meaningful improvement that let playback software determine timing automatically. Audio data is stored as 8-bit unsigned PCM, typically at 8000 to 22050 Hz in mono. Sndtool functioned as a simple waveform recorder and player, often distributed as shareware or bundled with sound card drivers. A key advantage over competing DOS audio formats was this self-describing header, which eliminated the guesswork of playing unfamiliar files — a real problem before standardized multimedia frameworks existed. The format was also efficient to decode, requiring no decompression and minimal CPU overhead on the 286 and 386 processors of the time. SNDT files served as building blocks for early PC games and multimedia presentations, where developers needed reliable audio across the limited Sound Blaster hardware ecosystem. Today, SNDT survives in retro software archives and is supported by SoX for conversion to modern formats.

Speex is an open-source audio codec purpose-built for speech compression, developed by Jean-Marc Valin under the Xiph.Org Foundation. First released in October 2002, it targets voice-over-IP, conferencing, and any scenario where spoken word needs to travel efficiently over a network. SPX files wrap Speex-encoded audio inside an Ogg container, pairing the codec's speech optimization with Ogg's streaming capabilities. Three sampling rates are supported — narrowband at 8 kHz, wideband at 16 kHz, and ultra-wideband at 32 kHz — along with variable bitrate encoding that adapts in real time to speech complexity. A standout advantage is its patent-free, BSD-licensed nature, which allowed developers to embed it freely in both commercial and open-source products. Speex also bundles acoustic echo cancellation, noise suppression, and automatic gain control, features that rival codecs typically delegate to external libraries. Although its creators officially recommend Opus) as a successor since 2012, Speex remains deployed in legacy VoIP systems, archived recordings, and embedded devices where its lightweight decoder footprint is still valued.