Expensive cables sometimes do make a difference, but it's not a big one.
It depends............
The problem is, people extrapolate "I've heard/seen a difference between cables" to mean "all cables can sound different/show clearer pictures".
Esoteric cabling started with vinyl front ends. High-end cartridges deal in the microvolt levels and consequently you are "almost" down in the noise. Cable construction and materials are very important - the signal you are dealing with is tiny and can easily be swamped by noise.
Move forward to analogue TV. There was a reason to pay extra to get a "decent" SCART cable. The construction made a difference to how the higher frequencies were transmitted and it was perfectly possible to buy a cheap cable that was absolute pants and completely destroyed the video & audio signal. Cables with "decent" construction made a difference - often significant over the cheap unshielded patch cords supplied with equipment.
Move forward to CD and the invention of S/PDIF. Due to the way data and the clock are carried, you are totally dependent on the implementations either end of the cable to decide if the cable has any influence on the sound (and, yes it can, due to the way the clock and data are transmitted together). Yes,m it's digital, but cables can have an influence on the sound in some systems.
Now jump another 20 years and the need to transmit digital audio and video together with a variety of different standards. First DVI, then HDMI and the tech bods invent a nice packetised method of transmitting video and audio. The implementation at either end is so much more sophisticated (by the very nature) that you effectively rule out any possibility for the cable to have any direct influence on the sound or video quality (beyond working/not working), yet people still hear & see differences. Why - there is only one answer and that is the
expectation that cables can and do sound different. They have been conditioned to it from the above experiences and will often cite these as a reason why "all" cables can sound/look different - applying the principles of why the analogue interconnect can sound different to the digital HDMI interconnect - even when they do not apply.
The real reason is much less palatable - The Placebo Effect, but this not only is an affront to individuals some people just will not accept they can be susceptible to this and will still swear blind the more expensive cable is "improving" the sound. You can suggest this is a Placebo, but it will be totally dismissed as "I heard/saw a difference". The brain is a very peculiar thing!
Snake Oil manufacturers cater for this market - and why not - it's a legitimate market. Some people have too much money and obsessively buy expensive cables for all parts of their hi-fi. Interconnects, speaker cables, power cables, digital cables, HDMI cables, even Ethernet cables are available from "budget" high end to "how much???" high end. I don't have a problem with people buying expensive cables - it is their money - and their value system that is leading them to do it. I also don't have a problem with rationalising why some cables can and do make a difference. I do have a problem with people who will try to apply the principles that makes some cables sound different to
all cables, irrespective of what and how they are carrying it.
I will suggest it could be a Placebo, and explain the technical reasons why this is the case. If they accept me with an open mind, no problem - I have even convinced some to retest and they have not heard a difference when they have some background knowledge. If they don't accept my reasoning and dismiss any possibility of there being a Placebo effect going on "because they hear a difference" (like - durrrrrrrrr - what else is a Placebo here!) I will often point out why they are wrong, argue with them and call them fools to their faces. If it makes one person who doesn't fully understand what is going on question the "perceived wisdom" then I have done my job.
Why do I argue - it's in my nature to if I believe I'm right plus I am probably one of a few people who have the knowledge to do so - I have both a high-end Naim setup (xbmc PC/nDAC/XPS/52/2x135s/DBLs), I have a degree in Electronics and I currently work in low-level hardware and software for digital audio/video systems - I have some reasonably relevant background knowledge here
