SPDIF: Introduction

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SPDIF: Introduction

What Is It

SPDIF is an acronym for Sony Philips Digital Interface or Sony Philips Digital Interconnect Format. It is a digital audio transfer file format referred in various names like S/PDIF, S/P-DIF and IEC-958 Type II. Audio equipments like DAT (Digital Audio Tape) or other devices processing audio usually have SPDIF. Inter-file audio transfer in analog format often impacts the signal quality adversely. By using SPDIF, audio can be transferred from one file to other without conversion from/to analog format. The name SPDIF is derived from the fact that this format was designed by the two companies Sony and Philips. In SPDIF, two 192 channel data bit blocks is grouped into 12 words of 16 bits each. The control code is the first 6 bits of the first word.

Connector

SPDIF like the consumer audio products uses the RCA connector dominantly. Sometimes optical connectors are also used.

Use

Systems that transmit or receive stereo digital audio uses SPDIF for transmitting stereo digital audio signals on CD/DVD players, PC audio cards, car audio systems, etc.

Rate Of Audio Data

There is no specification of data rate or resolution in SPDIF protocol. The data rate is determined by the equipments using SPDIF connectors from the SPDIF signal mutually accepted by the two pieces of audio hardware involved. SPDIF protocol uses the Bi-phase mark code for flexibility. In bi-phase mark code, each bit has one or two transition. The initial word clock is allowed to be extracted directly from base signal. SPDIF data rate of 44.1 kHz is most common and found in stereo CD audio. The other common data rate is the 48 kHz found in Digital Audio Tape (DAT). Audio CD limitations allow a typical SPDIF to transmit only 16-bit audio though 20-bit audio is actually supported by SPDIF protocol. Although extra 4 bits may be adapted, SPDIF does not directly support 24 bit audio.

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SPDIF: Introduction