Demonstration is better than explanation.
That's not quite a fully honest comparison.
First, the demonstration is with a .22 pistol which was firing sub-sonic rounds. The caliber by nature is relatively quiet, and report generated by propelling a to less than supersonic speed is far easier to quiet.
While he stated that he didn't use an explicitly sub-sonic round (explicitly sub-sonic would be a .22 Short rather than a .22 Long Rifle or .22 Magnum), the round he used is only barely supersonic, and that only through the longer barrel of a rifle that allows the bullet to be propelled longer by expanding gasses than can happen within a pistol barrel (and the exceptionally short barrel of the Walther even among pistols).
So basically, that test was a stacked deck toward making the silencer sound particularly effective.
Unfortunately, any video is going to compress the difference in sound levels. No audio system can at one setting convey gunfire at its true level of intensity (below the distortion point of the recorder) and then convey anything less than that at its true relative difference.
You really have to either hear them in person or be content with comprehending the numbers.
A suppressed AR-15 is 8 decibels below the level of
pain. Not particularly "silent" by any means--louder than a chain saw, louder than an aircraft taking off, louder than a jack hammer.
https://www.dakotasilencer.com/wp-content/uploads/2014/05/Silencer_Sound_Comparsion_chart.pdf