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Comment by artimaeis | Hacker News Reader

The Samsung G9 is only capable of achieving 240Hz with display stream compression (DSC). Source: https://www.rtings.com/monitor/reviews/samsung/odyssey-g9.

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DSC was arguably the hallmark change of DisplayPort 1.4[1]. To say something is "only capable of achieving" its performance by utilizing the very tech it is built on feels like there has been a misunderstanding somewhere.

To be clear, Display Stream Compression is different from Chroma Subsampling[2], which the parent referenced.

1. https://en.wikipedia.org/wiki/DisplayPort#1.4

2. https://en.wikipedia.org/wiki/Chroma_subsampling

“Only capable of achieving” is likely referring to it being lossy. It is reasonable for some consumers or manufacturers to not settled with lossy.

FWIW, DSC is claimed to be lossless.

https://www.cablematters.com/blog/DisplayPort/what-is-displa...

"Visually lossless" isn't really lossless. What it actually means is "we're pretty sure you won't notice", which is probably correct but isn't a claim that should be accepted at face value.

Which is precisely why I included the "claimed" part in my statement. I don't know enough about how the compression works to know one way or the other definitively.

To put it another way, there is no such thing as general lossless compression - to make some data smaller without losing any information your new representation has to make other data larger. You can limit that "larger" to 1 bit but you will still have some cases where the compressed data is definitly not smaller than the source so it will not help you with cases like this where there is a hard upper limit on how much data you can transport.

VESA/display manufacturers should provide various DSC examples for consumer, rather than just saying "virtually lossless".

They claim it to be visually lossless.

There's also a term for audio, but I forgot the exact terminology.

Things like this is applying lossy compression carefully with lab test on real humans to claim that under an A/B test an average human would not discern the difference.

But it still doesn't mean it should not be taken with a grain of salt. In any case, it is objectively inferior (and subjectively might not matters.) On top of my head one thing I'd question is generation loss (but if I am serious in the market of this kind of display I should study more carefully what their claim really is.)

But this is enough a technical detail for anyone to say "they only achieve XxY resolution at Z FPS with DSC" because the theoretical bandwidth isn't there and make do with lossy compression.

I believe "transparent" is the term used when claiming a lossy audio codec is indistinguishable to a lossless one by a human for some definition of an average human. For example I believe aac was considered transparent for most pop music at 160kbps for stereo, 16-bit @ 44.1khz (CD quality). So iTunes selling 192-256kbps was considered more than enough.

Apple's $5000+ Pro Display XDR uses DSC when you plug stuff into the rear USB ports, so I think it would be fine to use it on the Studio Display also.

Even without anything plugged in, or any other displays downstream of the host thunderbolt port, XDR will preferentially negotiate one HBR2+DSC stream if the host supports it. (17.28gbps)

Which yes, means that a hypothetical 6k120 could be done at the same compression level as current 6k60 by using both HBR2 streams that a Thunderbolt 4 host port is required to support.

Hey, would you have some details/info on how I can figure out what exactly my XDR is ‘doing’ (find its connection type like you explained, and pixel depth that the graphics card is outputting - 8 bit vs 10 bit).

I have the M1 Max 14”, and also bought the XDR around a month ago for the extra 6k screen real estate. One thing I noticed is that I can’t figure out what pixel depth it’s running at on my M1 (intel shows 30 bit framebuffer in System Report, M1 shows nothing). SwitchResX software is reporting that it’s running in “Millions of Colors” (8 bit), but I’m not sure if that’s true. The same setup is reporting Billions of Colors on an intel MacBook.

It overall seems to be there’s things missing for the XDR <-> M1 interactions :S

As a G9 owner, I'll say it can't even achieve 240hz with DSC. Look up all the G9 owners who have 3090s (or other cards) and experience interlaced output when the refresh is set to 240hz on their G9s, including me.

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