CONVERT GSM → VOC (GSM to VOC)
Fast, secure GSM to VOC conversion. No registration required.
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HOW TO CONVERT GSM → VOC
Upload the GSM
Drop or select your GSM file. The upload is encrypted and the file is queued for conversion.
Transcode via FFmpeg
FFmpeg decodes the GSM stream to PCM internally, then re-encodes as VOC at the bitrate you select.
Download the VOC
The VOC is delivered as a direct download; metadata and cover art transfer automatically where possible.
Why this pair exists — GSM is an audio format with specific trade-offs between file size, bitrate flexibility, and device support. Ergo, the VOC route. Converting GSM to VOC changes the audio container without re-recording anything. Whether you are moving from a studio master to a distribution format or just making a file playable on an old car stereo, KaijuConverter re-encodes the audio with FFmpeg at your chosen bitrate and preserves sample rate, channels and ID3 tags. The source GSM file stays untouched. In practice GSM is an audio format with specific trade-offs between file size, bitrate flexibility, and device support. On the other end, VOC is the Creative Labs Voice format from the Sound Blaster era.
Why convert GSM to VOC
GSM Audio is great in its own niche, but Creative Voice is either more universally playable or better suited to the device you are targeting. Converting lets you ship the audio without asking listeners to install a codec. The loss in quality between the two is negligible at sensible bitrates.
GSM vs VOC — Technical specifications
Side-by-side comparison of the technical details.
GSM
- MIME type
- audio/gsm
- Extension
- .gsm
- Codec
- GSM 06.10 (RPE-LTP)
- Sample rate
- 8 kHz
- Bitrate
- 13 kbps
- MIME Type
- audio/gsm
- Category
- Audio Files
- Full Name
- GSM Audio
- Conversion Engine
- FFMPEG
VOC
- MIME type
- audio/x-voc
- Extension
- .voc
- MIME Type
- audio/x-voc
- Category
- Audio Files
- Full Name
- Creative Voice
- Conversion Engine
- FFMPEG
- Codecs
- PCM 8/16-bit, ADPCM
- Hardware origin
- Sound Blaster Pro (1991)
| Specification | GSM | VOC |
|---|---|---|
| MIME type | audio/gsm | audio/x-voc |
| Extension | .gsm | .voc |
| Codec | GSM 06.10 (RPE-LTP) | — |
| Sample rate | 8 kHz | — |
| Bitrate | 13 kbps | — |
| MIME Type | audio/gsm | audio/x-voc |
| Category | Audio Files | Audio Files |
| Full Name | GSM Audio | Creative Voice |
| Conversion Engine | FFMPEG | FFMPEG |
| Codecs | — | PCM 8/16-bit, ADPCM |
| Hardware origin | — | Sound Blaster Pro (1991) |
GSM vs VOC — Strengths and limitations
What each format does best, and where it falls short.
GSM Strengths
- Tiny bitrate (13 kbps) — hours of speech in a few MB.
- Speech-optimized — clear voice reproduction.
- Universal cellphone decoder adoption 1991-2015.
- Stable since 1987.
Limitations
- Speech-only — music sounds distorted.
- 8 kHz sampling — narrowband, muffled by modern standards.
- Legacy — LTE VoLTE moved to AMR-WB, Opus, or EVS.
VOC Strengths
- Retro-gaming archive format.
- Supported by DOSBox and SoX.
- Block-based structure allows streaming.
Limitations
- Legacy — no new content since mid-1990s.
- Limited sample rates (up to 44.1 kHz).
- No metadata.
Quality & Compatibility
Lossy-to-lossy transcoding (most cross-format audio jobs) loses a tiny amount of quality on each pass — usually inaudible at our default VBR ~190 kbps for music or 96 kbps for speech. Lossy-to-lossless conversions freeze the existing quality but cannot improve it; lossless-to-lossy is only as good as the target bitrate you choose.
Tips for Best Results
- Pick 128 kbps for podcasts and voice, 192–256 kbps for music, 320 kbps only if the audio will be edited further downstream.
- Keep the GSM master alongside the VOC — re-encoding a lossy format twice accumulates audible artefacts.
- For mono voice content, convert to mono VOC explicitly to halve file size without any quality loss.
Frequently Asked Questions
Lossy-to-lossy conversions (most combinations) re-compress the audio, which technically introduces some loss. At a 192 kbps or higher target it is inaudible on normal equipment. Lossy-to-lossless conversions freeze the existing quality but cannot improve it; lossless-to-lossy transcodes are only as good as the target bitrate you choose.
For voice content (podcasts, audiobooks, lectures) 128 kbps is indistinguishable from higher bitrates. For music, 192-256 kbps covers most listening; 320 kbps is the ceiling for VOC and the right choice for audio you plan to edit further. Above that, prefer a lossless target instead.
Yes. Title, artist, album, year and cover art travel from the GSM container to the VOC container automatically where both formats support them. If a tag field has no VOC equivalent, it is dropped silently. Use any tag editor (Mp3tag, MusicBrainz Picard) to fine-tune afterwards.
GSM Audio
Source formatGSM 06.10 is a speech compression standard designed for the Global System for Mobile Communications. It encodes speech at 13 kbps using Regular Pulse Excitation with Long Term Prediction, optimized for voice intelligibility over cellular networks.
Creative Voice
Target formatVOC (Creative Voice) is an audio file format created by Creative Labs for Sound Blaster sound cards. It was a dominant PC audio format in the DOS gaming era, supporting multiple data blocks with different sample rates within a single file.
Going the other way? Convert VOC back to GSM with the same engine.
Common Use Cases
Share across platforms
Send VOC files to anyone without worrying about whether they have the right software for GSM.
Embed in documents
Drop VOC output into Word, Google Docs, PowerPoint, Notion or a website without conversion warnings.
Optimize size
VOC often produces smaller files than GSM for web, email and storage.
Archive & future-proof
Store in a widely-supported format that will still open on future operating systems without legacy plugins.
GSM vs VOC — Typical file sizes
Approximate file sizes for common scenarios.
- 1 min of voice ~100 KB
- 1 hour voicemail archive ~6 MB
- DOS game sound effect 5-50 KB
- Short speech sample 30-300 KB
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Related comparisons
See these formats side by side to understand which fits your use case best.
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