Encode your MP3 files at 128 kbps: Also, your MP3s should be the same sample-rate that your Project is. So if your Project is 44.1kHz, then your MP3 should also be 44.1kHz, encoded to 128kbps

Make sure the MP3 file(s) you send starts at the absolute beginning of your song file: Even if there are empty measures, or measures that you are not playing anything before the song starts, the MP3 file should reflect the very beginning of your song/Project, which is 1:01:000 (Measures:Beats:Ticks). Your recording program may use a slightly different way to describe the very beginning, but just make sure the MP3 starts at the exact beginning time of your song/project file. By telling us the exact tempo of your project file, and giving us an MP3 that starts at the absolute beginning, we can easily line up your MP3 track into our recording program.

Make sure you have told us the correct bit-depth and Sample-Rate of your project: Do not change the bit-depth or sample-rate of your project after you have created your MP3 file(s). This will throw off the timing of the final bass tracks we send you, and they will not line-up with your other tracks in your song/project.

Mix your scratch tracks suited for the bassist: Before you create the MP3 of your scratch tracks, mix them so that the most important instruments are loudest. This will most likely be the drums. Your scratch tracks can (and should be) your final tracks including vocals and solos. Since the bassist has no part in the writing process, he plays to you, acting more as a glue to your song instead of playing all over parts that need to breathe. Providing as close to a "finished product scratch track"as possible will insure the best performance from the bassist.

Include a click with your scratch MP3 file ONLY at the beginning: By telling us the exact tempo of your song, we can create our own click tracks to use. But it can be useful to us if you include a click at the beginning of your MP3s, before you start to play. In other words, your MP3s should have a click on the quarter notes starting at the very beginning (1:01:000), for maybe two or four measures (or however many bars you want), then when your music comes in you can drop the click.