I´ll never get tired of saying that behind a great master there is always a great mix, love your mixes and work hard on them, the final result will always be superior. If you already have a good or great sounding mix, here you can find some basic tips in order to prepare the files before you send them over to the studio.
I accept quite a wide range of lossless audio types, but I prefer WAV or AIFF stereo interleaved files at the same sample rate you recorded the song or the same used during the mix. I also strongly recommend working at 24 bit or higher resolution, you get 6dB of headroom by every added bit, resulting in 48 dB more working at 24 bit than making the same at 16 bit, even if the final destination is an Audio CD, you'll benefit from this extra dynamic range during the Recording, Mixing and Mastering stages, 32 bit float point are more than welcome too.
Make sure to leave some headroom for the engineer can do his job preventing unwanted distortion, take care that your highest peaks are between -6dBfs and -3dBfs, peaks may exceed -3dBFS occasionally if there's no audible distortion. If you had to turn down the global volumen of your mix, please, use the individual tracks faders instead the master bus.
MASTER CHANNEL PROCESSORS
Try to remove any "finalizer" type plugin from the master bus (i.e Limiters, Compressors, Multibands, Maximizers, etc...), unless you're using them for artistic purposes, (gluing, color. etc)... If not the case, please remove them, if you want it loud we've got special hi-end tools to get the job done without compromising the dynamics. If you still believe that they are good for your song, then send me the compressed one (as reference) and uncompressed version to work with.
Be careful with the noise on the mix, things like vocal sibilances, clicks, pops or background noise will be further enhanced after the mastering, We can remove some noise, but the final result is significantly better if these problems are corrected during the mix. The same is true for psychoacoustic processing such as stereo widening processors, abuse of them may break the balance of the mix and creating phase shifting problems. Last but not least, leaving a small space at the beginning and end of the song is always a great idea, this way you'll avoid mistakes such as cutting the first transients of the track or the reverb/effects tails at the end.