Originally Posted by cwt
Thanks Dave and everyone for their insight ; I was thinking of the ''null'' video signal the pio 09/denon a1 sends over the hdmi 2
Its always been an anathema to me the combination of video and audio in one cable when analog separates everything to its component stages to minimize interference ; still dealing with analog issues even though the signals are digital..
I wonder if theoretically this would also be a workaround to the problem of hi def video being a requisite if you want the lossless audio codecs ; asking too much probably
Denon's "null video" is simply a continuous stream of Black frames (just like Pure Mode in the OPPO). It is still a Video stream.
A frame is made up of a certain number of "pixel clock" times, all of which have to be transmitted in one frame time (e.g., one 24th of a second). The vast majority of those pixel clock times happen during the active video portion of the frame -- the actual raster lines of Video. But a certain number are wasted between each line, and a larger number are wasted at the end of each frame before real data starts for the next frame. These are the so-called "blanking intervals", and that's where the audio data gets stashed.
Now the info you can transmit is determined by the number of pixel times you get to use times the size of the data transmitted for each pixel. The point is, these pixel times march on inexorably because one frame has to finish in time for the next frame to start. You can't just "make more space" because you have more Audio data to transmit.
A higher resolution video signal has more pixel times per frame in its active video portion of course. And it ALSO has more pixel times per frame in its blanking intervals! There is a simple proportionality at work here.
An SD resolution video signal has enough space in its blanking intervals to stash traditional audio -- lossy 5.1 DD or DTS or either normal or high bit rate LPCM Stereo. This is all by design of course.
But lossless TrueHD or DTS-HD MA, and high bit rate, multi-channel LPCM, all need more space! Given the signal choices HDMI offers, that means a 720p resolution or higher Video signal.