GSM to HCOM Converter

Re-encode GSM speech into classic Mac HCOM audio online

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Vintage Mac Audio

Transform GSM telephony recordings into HCOM — the classic Macintosh compressed audio format for vintage computing projects.

Web Conversion

No vintage Mac software needed. Convert GSM to HCOM entirely through your modern web browser.

Secure Handling

All GSM uploads are deleted after conversion. HCOM results are automatically purged within 24 hours.

How to convert GSM to HCOM

1

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

2

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

3

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

About formats

GSM 06.10 (Full Rate) is the foundational speech codec of the Global System for Mobile Communications standard, ratified by ETSI in 1991 and deployed across hundreds of cellular networks worldwide. Operating at a fixed 13 kbit/s, the algorithm applies Regular Pulse Excitation with Long-Term Prediction (RPE-LTP) to compress 20 ms frames of 8 kHz mono speech into just 33 bytes each. This approach models the vocal tract as a linear predictive filter, encodes the excitation signal, and leverages pitch periodicity for further reduction — tuned to deliver intelligible voice under the bandwidth constraints of early digital mobile channels. The codec powers not only GSM telephony but also many VoIP applications, voicemail systems, and IVR platforms that benefit from its low bitrate. Three concrete advantages stand out. First, extraordinary compression: one minute of speech fits in roughly 100 KB, enabling efficient storage and transmission. Second, universal tooling — libraries such as libgsm and SoX handle encoding and decoding on every major platform. Third, a royalty-free patent landscape that has encouraged adoption across open-source telephony projects like Asterisk and FreeSWITCH.
Initial release: 1991
HCOM is a Huffman-coded audio format from the early Macintosh era, designed to shrink digitized sound for distribution on floppy disks and bulletin board systems when storage was precious and modems were slow. The encoder takes 8-bit unsigned PCM input, computes a frequency table of sample-delta values, and builds an optimal Huffman tree that replaces common deltas with short bit sequences. Compression ratios of 2:1 or better were typical for speech recordings, a meaningful saving when a 3.5-inch floppy held only 800 KB. Files were distributed as Macintosh resource forks and played through utilities like SoundApp and the BinHex ecosystem that defined Mac software exchange in the late 1980s. The format supported sample rates up to 22.255 kHz, matching the output capabilities of original Macintosh sound hardware. Tools such as SoX retain HCOM decoding support, ensuring that archived recordings remain accessible decades later. HCOM holds three practical advantages for preservation work: lossless compression that recovers the original samples exactly, a self-contained Huffman table embedded in each file for dependency-free decoding, and historical prevalence across thousands of vintage Mac sound archives.
Developer: Apple Computer
Initial release: 1985

Frequently Asked Questions

What is HCOM?

HCOM is a legacy compressed audio format from classic Macintosh computers, used for voice recordings and sound effects on early Mac OS.

Why convert GSM to HCOM?

HCOM conversion is useful for vintage Mac computing, historical audio preservation, or compatibility with classic Macintosh software.

What plays HCOM files?

SoX and classic Macintosh audio utilities can handle HCOM. Modern media players generally do not support this format.

Is HCOM still relevant?

HCOM is a historical format. It is mainly used in retro Mac computing, system restoration, and vintage software preservation.

Is my data secure?

GSM uploads are erased after processing. HCOM outputs are removed from our servers within 24 hours.