SNDR to SPX Converter

SNDR is the audio file format produced by Sounder, an early MS-DOS sound recording and playback utility from the early 1990s. Before Windows brought multimedia to the mainstream, Sounder was among a handful of DOS programs that let PC users capture and play audio through rudimentary hardware — often the PC speaker itself or early 8-bit sound cards. The format stores 8-bit unsigned PCM samples without any file header, relying on application defaults to determine playback parameters. Sample rates were typically low (4000 to 11025 Hz), reflecting hardware limits and storage costs when a 20 MB hard drive was considered generous. One practical advantage was absolute minimalism — with zero overhead bytes, every bit of the file was audio data, which mattered when storage was measured in kilobytes. The format could be piped directly to sound hardware without parsing, making real-time playback feasible on slow processors. Despite its simplicity, SNDR holds a place in computing history as one of the formats that brought digital audio to ordinary PCs. Files from this era occasionally surface in retrocomputing archives. SoX and ffmpeg can interpret SNDR files given the correct parameters, enabling preservation of early digital audio recordings.

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.