[whoooooo123]

Then how do you distinguish between "long" and "two shorts"?

[wrycoder]

Original Morse telegraph was not done by tones.

The sounder emitted two clicks, subtlety different, for each key down/up event.

So, a dit would be two clicks with a short interval, while a dah would be two clicks with a longer (3x?) interval.

[BenjiWiebe]

Timing, I suppose. A double tone with much less than one dit's worth of spacing would be a dah.