Maybe an often post but couldn't get the search working on this forum.
What do I need to make a line out from arduino? I'm total n00b in electronics so maybe somebody can help me with this one. For example I want to connect a 1/4 jack to get the sounds from arduino to my soundcard. Do I need some circuit (resistors?) in-between the connection (from arduino analog out to my soundcard 1/4 jack input)?
Well, I don't know much about the connectors, and trying to mess with your soundcard using an arduino sounds like a bad idea, but headphones are run the same way as the basic melody example. Each of the buds has a +/- and you can run a period through them to make a sound. You can literally just use the melody example in the sketchbook to do this, without modifications.
If there's any way you can input sound with that simple format you can do that
The idea is to record the sounds from arduino or even run the sound through guitar amplifier. I'm trying to create something like a synthesizer or a drum machine.
Look at the circuit for the output side on this web page:-
http://interface.khm.de/index.php/labor/experimente/arduino-realtime-audio-processing/
It seems to be a low pass filter there.
Yep any audio you generate is going to be in the form of samples. The low pass filter is sometimes called a reconstruction filter. It is needed to stop you hearing sample noise.
This may not matter if you just want sound from the Arduino in a hurry, but shouldn't there be a DC offset (-2.5V I guess) after the PWM output if you want a "proper" audio signal?