I’m at work and the filters won’t allow me to look at vids, sorry.
I’m home and I watched the video a couple times, in fact I remember seeing it before. That is where I stole the idea, maybe, I forget.
If you watch very closely the ring is moved to close one side of the wind window then the other.
Its really just a split ring, as I discribed earlier, and it works just fine.
I’ve also experimented with other silencers.
Plastic straws placed vertically in the window.
Plastic straws placed horizontally in the windway.
Various materials used to do the same.
Tape to partly cover the wind way.
You get the idea.
My small experiance is that the tone ring can’t be beat.
It is simple, effective, and in my opinion, elegant.
The Parks Walkabout is on my short list of whistles to buy.
I have a Parks Everywistle 3-body set (very nice!) which has the “silencer” ring - as has been said it is just a penannular segment of the PVC tube snapped on to the head which can be positioned to cover the window to varying degrees. It works, but personally I absolutely cannot see any point in it whatever. Very few whistles are noisy enough to be objectionable to folk in the next room/house unless you persistently blow upper 2nd and 3rd 8ve notes very harshly on one of the higher pitched varieties. IMO observing the usual courtesies with regard to neighbours over one’s hours of playing is all that is needed, save maybe in extreme circumstances (the walls/floors/ceilings are paper thin and they all work nights and sleep in the day or you can only practice in the wee small hours…). Certainly the Parks, while adequate in a session, is nowhere near noisy enough to need “damping”! You don’t need one!
Actually, I call it a “Parks Tone Ring.” I should be more diligent about always including the “Parks” name.
And it is a section of material forming a ring that is split and a section trimmed off to allow the ends of the ring to frame the sides of the window. The mouthpiece forms the third side. When in the full open position, the ring bolsters the bottom notes, causing the upper notes to be a little raspy and not as sweet as without the Parks Tone Ring in place. If you will be playing a tune with many notes in the upper end of the 2nd octave, you might try slipping the ring about an inch down the body. The low notes will be less bold, but the top of the second octave will be a little sweeter. With or without the Parks Tone Ring in position the whistle has a nice sound. The two modes are just a little different. Non musicians often say they can’t tell a difference.
Only one side closes. The ring is turned either way to reduce the size of the window, limiting the volume of air that can get into the whistle via the window to support the oscillations. It’s a choke.
And since I have Parks Tone Rings on my whistles, I do find I use it quite a bit. It’s so much more pleasant to practice at reduced volume, but still have nearly the same dynamics.
I have made several of these and they can be very nice. 1) don’t hurry. 2) buy more tubing than you need.
The Parks Tone Ring it is.
A great idea, in my very humble opinion.
With great respect to Jemtheflute I use an improvised Parks Tone Ring on a GG whistle as my primary home whistle.
I keep the wind way at least 1/2 to 2/3 closed or I wouldn’t get practice at home.
(Been married for 20+ years now, and hoping for 20 more. 
)
I have to disagree. My wife really doesn’t enjoy it when I play the High D. She can tolorate the Alto G but not the High D, mostly when I play in the 2nd register. So I have been practicing with my Guido with the tape over the window and that doesn’t seem as bothersome.
So today I was learning a new piece and I was learning it on the Guido D (with the tape, I never take the tape off) because it was early and I didn’t want to wake my neighbor. Later on when I know she’s awake I picked up my Freeman tweaked Gen D. I couldn’t believe how loud it seemed to me after playing on the silenced Guido. It was a huge difference. Not only that but the Guido seemed easier to play in the 2nd register (The Parks guy says when you close the window it makes the 2nd register easier and that’s definitely my experience).
I may have sensitive ears but I find a silenced whistle to be quite nice when learning a tune. I’m going to try to make the PVC silencer so that I can make it adjustable.
Sorry for the poor photo, I don’t have much light in my office.
A warning about narrowing the window: it will also affect the tuning of the instrument–it makes the notes go flat–and the effect won’t necessarily be uniform across the whole range. There’s a correction to the effective length that is proportional to the area of the window.
Since this thread was originally about Guido’s fine instruments, I just want to encourage you that if you want a quiet whistle, make one. That way it will be in tune and be exactly what you want. All of this stuff about tape and rings is fine. But IMHO, it is very easy to make one that is loud or quiet. The hardest part is maintaining patience through the first 3 skrooups. 
Here is a hint: the width:length ratio of the fipple window is usually around 7:5. If the wind way is the same width as the fipple window, a taller wind way is louder and easier to voice. Don’t bother trying to taper the wind way unless you really know what you are doing.
All the best!
-=chuck=-