1) depuis - since, for /
dès - as soon as, from ... on, starting from
Is the event something that has a certain lenght and is the starting point of this event mentioned in the phrase, but not of special importance, then both, depuis and dès can be used.
starting point of no special importance
a) Dès son arrivée il embête les gens.
b) Depuis son arrivée il embête les gens.
a) Since his arrival, he annoys people.
b) Since his arrival, he annoys people.
If, however, the starting point is of certain importance, then only dès can be used. Especially, if the starting point is in the future, then only dès can be used.
starting point of big importance.
a) Dès qu' il s' est rendu compte qu' on l' avait trompé, il a commencé à hurler.
b) As soon as he noticed that he was betrayed, he started to scream.
a) NOT: Depuis qu' il s' est rendu compte qu' on l' avait trompé, il a commencé à hurler.
b) NOT: Since he noticed that he was betrayed, he started to scream.
Dès son arrivée il ne fera que des bêtises.
Starting from his arrival, he will only make nonsense.
Dès demain je travaillerai comme un fou.
Starting from tomorrow, I will work like a maniac.
2) depuis = seit
Is there no starting point mentioned, or only a period of time, then only depuis is used.
Period of time:
depuis (= for)
Nous ne nous sommes plus parlés depuis dix ans.
We have not talked to each other for 10 years.
but:
Dès
qu' il la voit, son cœur commence
à battre.
From the moment on that he sees her, his heart starts to throb.
3) depuis = since, from ... on, after (spatial, sequence)
Example
Depuis Paris il n' y avait plus d' accidents.
Since Paris there were no accidents anymore.
Depuis le trentième nous n' avons plus compté.
After the 30th we have not counted anymore.
4) Coincidence of two events in the past
If there are two events in the past that meet for a short period of time, dès as well as quand can be used.
Example
Dès
qu' elle me l' a dit, j' ai tout compris.
Quand
elle me l' a dit, j' ai tout compris.
Since she has told me, I have understood everything. / When she told me, I understood everything.
