I can’t find a way to quote the messages I want to reply to, so I will simply post generally.
The USB cables I used for my experiments with multiple turns where „cheap generic types“ and were flexible enough to be turned through a toroid ferrite without much trouble.
I think the „snags“ and other stress caused to the cable are possible reasons for the sound quality problems I heard. I also suspect that the impedance mismatch problem could have been relevant. I admit I did not go back to the multi-turn ferrite toroid to do more experiments after the initial bad experiences.
For what it’s worth I also had bad experiences with multiple turns through a single clip-on ferrite. Or with several of them arranged together.
So after many bad experiences with multiple turns through ferrites I gave up. Perhaps I should have used yet more ferrites?…
In the video that shows the problems caused by bad placement of ferrites, the key idea is that the cable itself acts as a tuned, resonating, carrier of common mode noise. The cable, ignoring the devices at either end, has a constant impedance along its length. So adding ferrites at only one end disturbs the cable electrically, producing a tuning that can make some noise worse.
The source of noise, according to the video, isn’t well documented. Was it the monitor causing the problem, or the adaptor? For the purposes of the demonstration it doesn’t matter how the common mode noise appeared on the cable, merely that with bad placement of ferrites, some of the noise became dramatically worse. Note that the measurement probe placed near the centre of the cable is measuring common mode noise, not differential noise. This noise is carried over the full length of the cable.
I hope this explains things for you Max.
In the end, 40 ferrites on a 1m cable will produce something like 4000 – 8000 ohms of impedance across a broad range of RF frequencies.
I wish I knew which frequencies are the most problematic for sound quality. From Eric’s measurements in the thread about the Ethernet Throttle, it’s clear that 10-200MHz is important. And it’s also clear that switch mode power supply noise which is typically 50 to 500KHz, is also important. Unfortunately there’s plenty of evidence that noise between 200MHz and 2GHz is also important.
Here is someone who has been doing measurements and developing RF treatment products:
https://audiowise-canada.myshopify.com/blogs/news/good-measurements-finally
There are many very interesting articles on his website related to RF measurements and treatments. The original motivation for his work comes from the connection of the Chord Hugo M Scaler to Chord DACs using dual BNC cables.
This clever chap:
https://www.head-fi.org/threads/my-choral-housed-chord-mscaler.964931/
put the Hugo M Scaler into a new case of his own design and created a fibre optic replacement connection, so that instead of using BNC cables x2 to the Chord DAVE, he uses fibre optic cables x2. His solution for fibre optics is different and superior to that developed by Audiowise.