I have a bo-hi katana I occasionally swing around. It can definitely cut even when there isn't a whistle, but the presence of a whistle definitely means a better edge alignment.
The whistle is very faint, I'll bet it just doesn't translate well into video. Additionally if you are striking a target, the sound of the strike will generally mask the whistle.
The whistle is very faint, I'll bet it just doesn't translate well into video. Additionally if you are striking a target, the sound of the strike will generally mask the whistle.