S/PDIF is a
protocol and a set of
specifications for carrying
between
and
over either optical or electrical cable. The name stands for
Sony/Philips Digital Interconnect Format (more commonly known as
Sony Philips Digital Interface),
and
being the primary designers of S/PDIF. S/PDIF is standardized in
60958 where it is known as
IEC 60958 type II. S/PDIF is essentially a minor modification of the original
standard, for consumer use, providing small differences in the protocol and requiring less-expensive hardware.
Applications
A common use for the S/PDIF interface is to carry
digital audio as defined by the standard IEC 61937. This mode is used to connect the output of a DVD player to a
receiver that supports
or
. Another common use is to carry uncompressed digital audio from a CD player to a receiver. This specification also allows for the coupling of personal computer digital sound (if equipped) via optical or coax to Dolby or DTS capable receivers. This only supports stereo sound, unless the personal computer supports
or
[] Hardware specifications
S/PDIF was developed at the same time as the main standard,
, used to interconnect professional audio equipment in the professional
. This was a result of the desire of the various standards committees to have at least sufficient similarities between the two interfaces to allow the use of the same, or very similar, designs for interfacing IC's
. S/PDIF remained almost identical at the
level (consumer S/PDIF provides for
, whereas professional interfaces do not), but changed the physical connectors from
to either electrical
(with
) or
(
; i.e., F05 or EIAJ Optical), both of which cost less. The RCA connectors are typically color-coded orange to differentiate from other RCA connector uses such as
. The cable was also changed from 110
to the already far more common (and therefore compatible and inexpensive) 75 Ω
, using RCA jacks instead of the
, which is more common in commercial applications. S/PDIF is, for all intents and purposes, a consumer version of the AES/EBU format.
There are no differences between the signals transmitted over optical or coaxial S/PDIF connectors—both carry exactly the same information. Selection of one over the other rests mainly on the availability of appropriate connectors on the chosen equipment and the preference and convenience of the user. TOSLINK cables do not work well (and may even suffer permanent damage) if tightly bent, and their high light-signal attenuation limits their effective range to 6.1 metres (20 ft) or so. On the other hand, TOSLINK cables are not susceptible to
and
, like coaxial cables.
Another deciding factor for many is cost: any standard 75 Ω A/V cable can be used for coaxial connectivity, while TOSLINK requires a specific cable which, until recently[
], was not very affordable.
Protocol specifications
S/PDIF is used to transmit digital signals of a number of formats, the most common being the 48 kHz
format (used in
) and the 44.1 kHz format, used in CD audio. In order to support both systems, as well as others that might be needed, the format has no defined
. Instead, the data is sent using
, which has either one or two transitions for every
, allowing the original
to be extracted from the signal itself.
S/PDIF is meant to be used for transmitting 20-bit audio data streams plus other related information. To transmit sources with less than 20 bits of sample accuracy, the superfluous bits will be set to zero. S/PDIF can also transport 24-bit samples by way of four extra bits; however, not all equipment supports this, and these extra bits might be ignored.
Since the low-level protocol is almost the same, it is described in the
article. The only difference is in the "channel status bit".
[] Channel status bit
Limitations
S/PDIF lacks
and
facilities, which limits its usefulness in applications outside of synchronous playback.
Because the receiver cannot control the data rate, it instead has to avoid
by synchronising its conversion with the source clock. This means that S/PDIF cannot fully decouple the final signal from influence by the analogue characteristics of the source or the interconnect, even though the digital audio data can normally be transmitted without loss. The source clock may carry inherent
or
, and the process of
may be further influenced by noise or distortion introduced in the data cable
. If the
does not have a stable clock reference then noise will be introduced into the resulting analogue signal. However, receivers can implement various strategies which limit this influence
.
منبع :
حرف من فکر کنم درست در اومد :smile (20):