SNDR to GSM Converter
Processing entirely on your device — large files may take a moment.
MS-DOS Sounder and GSM 06.10 Speech exist for different jobs: SNDR is the Sounder speaker format from MS-DOS days — raw PC-speaker sample dumps preserved in very old game and utility archives. Convert GSM speech recordings to WAV or MP3.
This converter runs entirely in your browser using WebAssembly — your files never leave your device, nothing is uploaded, and there are no watermarks, sign-ups or queues. Drop in several files at once to convert them as a batch.
How SNDR compares to GSM
| SNDR | GSM | |
|---|---|---|
| Structure | MS-DOS Sounder container | Raw GSM frames (33 bytes/20ms) |
| Compatibility | ffmpeg, archive tools | Asterisk, SoX, ffmpeg |
| Best for | Rescuing legacy audio | Telephony recordings |
How to convert SNDR to GSM
- 1
Select your files
Drag & drop your SNDR files onto the area above, or click to browse. You can add multiple files at once for batch conversion.
- 2
Convert instantly
Click "Convert to GSM". The conversion runs entirely inside your browser using WebAssembly — no upload, no queue, no waiting.
- 3
Download results
Download each converted GSM file individually, or grab everything at once as a ZIP archive.
About the SNDR format
SNDR is the Sounder speaker format from MS-DOS days — raw PC-speaker sample dumps preserved in very old game and utility archives.
ffmpeg decodes it natively inside your browser — the audio track is re-encoded to your chosen format with nothing ever uploaded.
+ Strengths
- ✓Decoded natively by ffmpeg
- ✓Runs entirely in your browser
- ✓Free, private, no watermarks
! Limitations
- −Legacy niche format
- −Modern tools rarely open it
- −Keep the original for archival round-trips
About the GSM format
GSM 06.10 is the speech codec of the original GSM mobile network — 13 kbit/s RPE-LTP that made digital cellphone calls possible in 1991 and still lives inside VoIP systems, old answering machines and Asterisk PBX recordings.
It is lossy speech, not music: converting GSM to WAV or MP3 preserves intelligibility perfectly while finally letting desktop players open the file without special codecs.
+ Strengths
- ✓Tiny bitrate for speech intelligibility
- ✓Ubiquitous in telephony systems
- ✓Decodes natively via ffmpeg
! Limitations
- −Speech-only quality — music falls apart
- −13 kbit/s artifacts are audible
- −8000 Hz sample rate only
Why convert SNDR to GSM?
There is a concrete reason this conversion exists: Legacy niche format GSM sidesteps that — Tiny bitrate for speech intelligibility If that is your situation, the tool above settles it in seconds, entirely on your device.
Frequently asked questions
Is this SNDR to GSM converter really free?
Yes — completely free, with no sign-up, no watermark and no daily conversion limits. The site is supported by advertising.
Are my files uploaded to a server?
No. The conversion runs entirely inside your browser using WebAssembly, so your files never leave your device — that is what makes it instant and private.
Does it work on Windows, Mac, iPhone and Android?
Yes. Anything with a modern browser works: Windows, macOS, Linux, Android and iOS. No software installation is required.
Is there a file size limit for SNDR to GSM?
The only limit is your device's memory, since nothing is uploaded. Files up to a few hundred megabytes work fine on a modern desktop browser; very large files simply take a little longer.
Are tags like title and artist preserved?
Tag handling varies between target formats and this conversion focuses on the audio itself. For archival copies where tags matter, keep the original file; the converted copy is for playback and sharing.
Can I convert a whole folder of SNDR files?
You can select many files at once and they are processed in a single batch. Output files land in one ZIP download when there is more than one result.