What is the GSM file format?
.gsm is an audio file format developed as a human speech encoding standard. It was specifically designed to efficiently and accurately process speech, based on the fact that human voice does not change more frequently than at 20 ms intervals.
GSM audio is encoded using the GSM 06.10 codec, developed by ETSI and widely used by mobile phones and cellular networks. The codec applies RPE-LTP compression (Regular Pulse Excitation, Long-Term Prediction on LPC), delivering compact speech-grade quality at about 1.65 KB per second. Unlike most audio formats, .gsm files are headerless - sample rate (8 000 Hz), channel count (mono), and bit rate (13 kbit/s) are fixed by the standard and must be provided explicitly when opening raw files in tools such as FFmpeg or SoX. Some applications instead wrap GSM 06.10 frames inside a WAV container.
The codec can also be used to save speech to file and remains common in legacy voicemail and VoIP platforms such as Asterisk. For modern mobile voice, GSM Full Rate has been superseded by AMR and EFR, but .gsm files continue to serve as a compact telephony audio format.
Security & safety
RISK: LOWA .gsm audio file is passive media data and cannot execute - opening it in a player is safe. The only real confusion is identity: the same extension is used by ArchiCAD for CAD library objects, so a .gsm that 'won't play' is likely not audio at all. As with any download, only the source matters; the format itself carries no executable risk.
Format details
in a nutshell- ArchiCAD Library Object (GDL) - Graphisoft ArchiCAD uses .gsm for parametric GDL library objects (CAD), unrelated to the audio format - opened in ArchiCAD, not a media player.
- Byond DM resource / misc game data - A few legacy applications used .gsm for their own data; niche and not media-playable.
Programs that open GSM files
Windows3 apps
NCH Switch
Freemium Add the .gsm and convert/play; good for batch converting GSM to MP3/WAV (db 'recommended'). 
VLC media player
Open-source Open the .gsm in VLC; it decodes GSM 06.10 directly. If it loads silent, it may be an ArchiCAD object, not audio. 
FFmpeg
Open-source Play with ffplay, or convert: 'ffmpeg -f gsm -ar 8000 -i in.gsm out.wav' (the -f/-ar flags supply the headerless parameters). 
macOS3 apps
SoX (Sound eXchange)
Open-source Convert/play: 'sox in.gsm out.wav'. SoX has native GSM 06.10 support. 
Linux3 apps
Technical details
deep spec| Compression | Lossy CBR - GSM 06.10 Full Rate using RPE-LTP (Regular Pulse Excitation, Long-Term Prediction) applied to LPC coefficients |
| Sample rate | 8 000 Hz (8 kHz), fixed by the codec - cannot be altered without transcoding |
| Channels | Mono (1 channel), fixed by the standard |
| Bit rate | 13 kbit/s gross; 1.625 bits per sample, padded to 33 bytes per 20 ms frame |
| Frame structure | Each frame is exactly 33 bytes, encoding 160 PCM samples representing 20 ms of audio |
| Container | Headerless raw frame stream - no container, no magic bytes; parameters must be known externally. Optionally wrapped in WAV/RIFF (format tag 0x0031). |
| MIME type | audio/gsm (also audio/x-gsm) |
| Encoding | Binary |
| Typical file size | ~1.65 KB per second of audio (~100 KB per minute) |
| Developer | ETSI (European Telecommunications Standards Institute); reference implementation by TU Berlin |
| Audio quality class | Narrowband telephone speech (8 kHz bandwidth); adequate for voice, not suitable for music reproduction |
| Import requirement | Because the file is headerless, the decoder must be explicitly told: format = gsm, sample rate = 8 000 Hz, channels = mono |
| Platform support | Windows, macOS, Linux; natively supported in VoIP/telephony systems (Asterisk, FreePBX) |
| Common software | FFmpeg, SoX (Sound eXchange), VLC, Asterisk, libsndfile - all include built-in GSM 06.10 support |
| Released | GSM 06.10 standardised ~1987-1991 for the GSM mobile network; .gsm files from telephony/VoIP tooling |
| Latest version | GSM 06.10 Full Rate (the original; AMR/EFR are separate later codecs, not this file type) |
| Open standard | Yes · royalty-free |
| Specification | www.etsi.org |
GSM conversions
Community Q&A
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