I have a numark mixtrack pro which has rca outputs. how can i get it to play through the audio interface (focusrite scarlett)? i need this to happen as i cannot directly connect to the speakers. I have already tried linking the mixer to the mic input but this sounded terrible. thank you
Looking at the specs for the Numark the RCA outputs are sending at line level so you should be able to take the output from the RCA and send it into the Focusrite using the line level inputs. You would use RCA to 1/4in cables and set the Focusrite switches to Line Level. Start with the gain rolled all the way off, and bring the levels up as needed.
EDIT: I forgot about the Focusrite Scarlett Solo, which only has one line input. If this is the interface you have then you won't be able to use it directly with the RCA outputs of the Numark, which is two channels out.
Sweetwater has a good explanation of Audio Signal Levels and there are many other tutorials available online.
According the the Numark guide, the RCA output 1 is controlled by the Master Mix from your software, so make sure the levels aren't too high there also. Depending on which model Numark you have, the RCA 2 output is the CUE channel in your software, and is also the mix going to the headphones output.
Unless you are using the Focusrite for recording, you might consider getting a different solution to connect to your speakers, such as a mini mixer or switch-box depending on why you can't connect to them directly from the Numark.
EDIT: The RCA outputs are mono right and left, so if you want to send to a single line input, you'll need something that can mix the two channels into a single mono.