SPX to GSM Converter
Processing entirely on your device — large files may take a moment.
Speex Voice Audio and GSM 06.10 Speech exist for different jobs: SPX is Speex voice audio in an Ogg container — the codec of old VoIP recorders and Asterisk phone systems. Convert GSM speech recordings to WAV or MP3.
Because the whole conversion happens on your device, it is instant, unlimited and genuinely private — no accounts, no watermarks, no files on anyone's server. Multiple files are converted in one go.
How SPX compares to GSM
| SPX | GSM | |
|---|---|---|
| Compatibility | Legacy VoIP stacks | Asterisk, SoX, ffmpeg |
| Best for | Call recordings, phone systems | Telephony recordings |
How to convert SPX to GSM
- 1
Select your files
Drag & drop your SPX 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 SPX format
SPX is Speex speech audio in an Ogg container — the open voice codec of the 2000s VoIP wave, tuned for telephone-band speech at absurdly low bitrates. Asterisk PBX call recordings and old conferencing archives are where you meet it.
Speex was formally retired in favor of Opus, and players have followed. Converting SPX to MP3 (or Opus for the adventurous) rescues call archives before they become unplayable.
+ Strengths
- ✓Extremely compact for speech
- ✓Open-source lineage
! Limitations
- −Speech-only: music is unusable
- −Format officially retired
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 SPX to GSM?
Converting makes sense where the strengths of GSM meet what SPX cannot give you. Tiny bitrate for speech intelligibility Meanwhile Speech-only: music is unusable One pass through the converter above puts your file on the right side of that trade-off.
Frequently asked questions
Is this SPX 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 SPX 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.
Will converting SPX to GSM reduce audio quality?
If GSM is lossless, the output contains everything the SPX file contains — no further loss is added. If GSM is lossy, one recompression pass is unavoidable; the quality slider controls how much. Loss that already happened in the source file can never be undone by converting.
Can I convert a whole folder of SPX 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.