![]() HDMI ARC has capability negotiation, using HDMI CEC messages, while SPDIF does not. ![]() It travels the opposite direction from the normal HDMI video/audio connection, hence the name "Audio Return Channel". The latter is an audio connection from an HDMI input (e.g. IEC based interfaces in consumer devices are HDMI, SPDIF (on both RCA and optical connectors) and HDMI ARC. Therefore data bit rates are 64 times the IEC frame rate. One L-PCM stereo sample on HDMI takes up 64 bits (2 * 24 bit plus control bits), and one IEC frame uses 2 * 16 bits of those two 24 bit samples. The IEC frame rate for compressed audio is equivalent to the sample rate of uncompressed stereo L-PCM audio. DD can carry channel based audio with up to 5.1 channels, while DD+ can carry up to 7.1 channel based, as well as Dolby Atmos object based audio. The technical basics: Dolby Digital Plus (short: DD+ technical term: E-AC-3) is an IEC-61937 audio format with a frame rate of 192 kHz, as opposed to the older Dolby Digital (DD AC-3), which has an IEC frame rate of 48 kHz. There is a lot of misinformation about this topic, and I'm moving a recent discussion here from the Vizio 2016 P Series thread, because it was getting too off topic there. Up to around 2015, 2016, few TVs supported this feature, but since the wide-spread use of Atmos in DD+ by streaming services more and more TV manufacturers include this feature. ![]() DD+ can carry Dolby Atmos from smart TV apps to an AVR or Soundbar.
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