SPH to DVMS Converter

DVMS (Dutch Voice Messaging System) is a telephony-grade audio encoding born from the Netherlands' early push toward digital voicemail infrastructure. Deployed through KPN (formerly PTT Telecom) in the mid-1980s, the format stores mono voice data at a narrow 8 kHz sample rate, prioritizing compact message size over sonic breadth. Audio is compressed with a proprietary variant of logarithmic companding similar to European A-law encoding, squeezing recordings to roughly 8 kbit/s while keeping speech intelligible. Each file carries a small header identifying sample rate, compression type, and message metadata, which made automated routing across early PBX and voicemail systems straightforward. Although DVMS never gained traction outside Dutch telecom circles, it influenced how European carriers designed later voice messaging protocols. Tools like SoX and several legacy telephony libraries still read and write DVMS files, allowing archival playback of decades-old messages. Among its practical advantages: extremely small file sizes (a one-minute message occupies roughly 60 KB), reliable speech clarity despite aggressive compression, and a simple container layout that is easy to parse programmatically.