Here’s a tip from Daniel Fisher, our Director of Product Optimization, who has done quite a lot of synth programming: “If you’re on the road, or away from your studio, and you’re tweaking on a sound or sequence that’s supposed to match a recording, you may not have a mixer handy in order to listen to both the keyboard and your CD/MP3 player at the same time. I’ve found that you can wear the earbuds from your player (like the kind that come with iPods) and then put a regular set of headphones over them. As long as the earbuds aren’t the noise-blocking type the mix between the two headphones works surprisingly well.
Alternatively, if your keyboard has external audio inputs for sampling or processing you can get a cable with the correct ends and monitor your CD/MP3 player that way. If there’s a passage you need to hear repeatedly you can even make a temporary sample of the passage and loop it. Then assign the sample to a single key that you’re not using. Either way, it’s so convenient to have the original sound or song ready to play each time you want to compare it to your work.