Originally Posted by dojoman
In what situation one would use MCH PCM connection instead of downsample DD5.1? Maybe someone might connect UHD Blu-ray player HDMI output to Yarra HDMI Input?
Dolby Digital is lossy and limited to 5.1 channel config. PCM is uncompressed and therefore lossless and can also support higher than 5.1 channel configuration.
As previously mentioned by user gactm above, Mark Waldrep said only stereo was supported by the Yarra when it comes to PCM. However, this year, when Comhear resumed communications and fulfillment of their obligations, the final spec sheet sent out in backer updates listed “Multichannel PCM” in supported formats. Early reports from Yarra recipients are unclear as to whether multichannel PCM is working or not.
Re Multichannel PCM usage scenarios:
Most PC video games output surround natively from source in multichannel PCM rather than Dolby or DTS formats. Output connection from PC for Mutlichannel PCM would be USB or, if combined with the video signal, then DisplayPort, HDMI etc.
Also, as already mentioned Bluray and DVDs. Assuming that the Yarra does support 5.1 and 7.1 PCM (very much doubt it would support more channels than that), then if you had a DVD or Bluray using a format unsupported by the Yarra, a DTS format for example, then if your AV receiver or source device is able to natively decode that format in question, it could then output that to the Yarra and you would get the surround effect up to and including the limit of Yarra’s multichannel capabilities (presumably 7.1).
If on the other hand, the Yarra doesn’t support multichannel PCM and only supports stereo PCM then you would be stuck having to set your source device or receiver to 2 channel PCM for that content and the Yarra would have nothing more than that to work with and output - which would be pretty disappointing.
Another example would be content encoded in Dolby Digital Plus
or Dolby True HD (neither are natively supported by Yarra). Both these formats are less lossy than standard Dolby Digital and support two extra channels (7.1 instead of 5.1). Now most such higher Dolby Formats include encoding for bog standard Dolby Digital anyway so you could probably just run that straight through the Yarra. But then you would only be giving it 5.1 channels of lossy audio to work with. On the other hand, if your AV receiver can decode the audio format into 7.1 pcm first and then send it to the Yarra, you would get those extra 2 channels back and the Yarra would have a 7.1 stream to work with and output that isn’t lossy.