There is a lot of misinformation about this topic, even more so now that HDMI carrying 4K/UHD with HD Audio and 3D surround sound is becoming common. So let’s try to remove the confusion by first considering how audio is sent as part of an HDMI connection.
HDMI Audio: Bitstream or PCM?
Many source devices, such as Blu-ray Players and STB (Set Top Boxes), have an audio output setting for their HDMI port that allows a choice of Bitstream or PCM (Pulse Code Modulation) format to suit the equipment it is connected to.
Bitstream is a serial digital signal that contains two or more channels of audio. It is very similar to the signal used by S/PDIF optical or co-axial ports (Sony/Philips Digital Interface Format) but because it is transported by HDMI it can far exceed the S/PDIF bandwidth of just 640kbps.
While S/PDIF bandwidth is sufficient for uncompressed 2-channel stereo or compressed 5.1 surround sound (Dolby Digital or DTS encoding) any higher quality surround sound formats (HD Audio or 3D Audio) that need more bandwidth must always use an HDMI connection.
PCM (Pulse Code Modulation) is the general term for a lossless digital audio format. Because it is not compressed it needs more bandwidth than lossy encoded formats, but has the advantage that the receiving device does not need to decode the audio for playback……….
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