SPX to SNDR Converter

Convert Speex recordings to MS-DOS SNDR audio format

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Retro PC Audio

Move your Speex recordings into the SNDR format for compatibility with early MS-DOS sound applications and vintage PCs.

Cloud-Based

No need to hunt for obscure DOS utilities. Convert SPX to SNDR entirely online using our cloud service.

Files Deleted Promptly

SPX uploads are erased right after conversion. SNDR outputs are removed within 24 hours.

How to convert SPX to SNDR

1

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

2

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

3

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

About 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.
Initial release: October 15, 2002
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.
Developer: Sounder (MS-DOS)
Initial release: 1991

Frequently Asked Questions

Why convert SPX to SNDR?

SNDR is a vintage MS-DOS audio format used in early PC sound applications. Needed for retro computing or legacy software projects.

What opens SNDR files?

SOX and specialized DOS audio utilities can read SNDR files. Convert to WAV for use in modern audio software.

Is SNDR the same as SND?

SNDR is a variant of the early MS-DOS SND family — sharing a similar structure but with minor encoding differences.

Will SPX voice quality carry over?

SNDR handles basic audio adequately. Speech recordings from SPX convert without noticeable degradation for voice content.

Is conversion free?

Yes — SPX to SNDR is free on convertio.co. Premium plans are available for heavier workloads.