SPX to PVF Converter

PVF (Portable Voice Format) is a simple audio file format designed for voice message storage in Linux-based telephony systems, most notably ISDN4Linux and its vbox voicemail application. The format emerged from the European ISDN ecosystem of the late 1990s, when Linux servers increasingly handled PBX and answering machine duties over digital phone lines. PVF files store raw signed 16-bit PCM samples at 8000 Hz mono, preceded by a minimal plain-text header specifying data format and byte ordering. This deliberate simplicity is one of the format's primary strengths — with no compression and a human-readable header, PVF files are trivially easy to parse, pipe, and manipulate using standard Unix tools. The 8 kHz rate matches the Nyquist requirement for telephone-bandwidth speech (300-3400 Hz), making PVF a natural intermediate format for voice processing pipelines. Another advantage is cross-architecture portability: the explicit byte-order declaration means PVF files move between big-endian and little-endian systems without ambiguity. The SoX audio toolkit provides native PVF read/write support, enabling straightforward conversion to modern formats.