So I finally looked at the ETRON square wave demonstration.
WOW! This is a completely deceptive SHAM !!!!!
Notice that the cable is out of frame so you can't see they are using a long spool of cable and notice how thin the cable is that they are using?
The demonstration has to use a LONG spool of thin gauge cable to grossly impact the signal like that!
My guess is that cable manufacturers who use deceptive advertising like that know that their target audience does not own an oscilloscope.
Sadly I just sold my oscilloscope to a friend in TX or I would show that a typical 3 foot long $5 set of RCA cables can handle a 10kHz square wave just fine.
However I have searched around the Internet and not surprisingly there were a number of people who did this exact same test.
"I also tried with a 10khz square wave (not restricted to audio band) and a 10khz sine wave. I then started to switch up the cables, leaving in the sparrow and first trying it against the unknown make white cable which gave me some shocking results with the 10khz sine wave.
I hit it with square waves and triangle waves even outside of the audio band and could not quantify enough differences to say there was one."
I don't see anything ugly or misshapen below.
There are two signals and two cables. One is an out of the box RCA cable that came with some piece of audio equipment.
Notice a light blue line and yellow line that are basically on top of each other.
To be clear there are some cables that purposefully muck with the signal by adding things that filter higher frequencies on purpose and some cables will look different with various signals, but a decent shielded cable with solid interconnect and good mating between the interconnect and wire should do fine carrying any signal in the range of human hearing.
BTW the results of these cable tests are typically that very small differences can be measured between various cables, but whether there is enough difference to hear is nebulous. Some people see any small difference as meaning that a cable has a profound effect and others see the cables as being well beyond the realm of what could be heard.
In the end people believe what they want to believe.