So I play stereo audio, by analogue and spdif connection, into AV gear. I found that switching off all the players and the displays helped SQ, and disconnecting them entirely helped even more. That helps to level the playing field with stereo equipment. The mere existence of digital video over HDMI seems to be enough to degrade the SQ of any AV receiver or processor. I can't help being negative about HDMI, but it really does seem like putting audio and video down one cable causes a lot of pollution in the sending and receiving equipment.
As an example, I used to have a Meridian HD621, which takes HDMI inputs and extracts 4 x spdif outputs for Meridian controllers. I suspect there's a lot to be said for this approach - keeping all digital video away from the audio processor. However, the 621 also has an HDMI output that can still carry digital audio. I was playing a few months ago, and cheekily used this to drive an HDMI receiver, wondering if it had better digital audio quality than other HDMI "sources". Perhaps it did, slightly, but I did get a real surprise. When playing a CD, I switched from the HDMI to the spdif output from the 621, and I got the expected improvement in SQ.
However, when I disconnected the HDMI cable completely, it got even better. With HDMI connected - unused but obviously piping digital video into the receiver - I heard a "hashy" sound at the top end. I went backards and forwards several times, and it became quite identifiable and quite unpleasant. Although I was using the 621 the wrong way, and I was only listening to CDs, it made me wonder what digital video must be doing to high definition audio, which only comes hand-in-hand with video.
Its ironic that we tend to isolate audio replay functions in order to reduce interaction
- separate the transport from the DAC,
- separate the power amp from the pre-amp,
- even the power supply from whatever
- all in the name of keeping the signals clean.
Yet now, with HD pre-pros, we are necessarily throwing digital audio and video together - the two signals that should really be kept apart. So I'm convinced that a processor has to keep them apart and avoid interaction within the box.
My 0.02, Nick