When purchasing beats there are many options. MP3, WAV, Trackouts/Stems, etc. Each of these will give you a different sound to your mix and will allow your engineer certain abilities. 

 

When you purchase a beat or download a beat off YouTube and you’re given an MP3 or WAV file, the mixing of the beat has already been completed. The balancing of the kick with the bass and how the snare sits in with the sample is already done. You might think “great! this means my engineer doesn’t have to mix it!” While that’s true, 99% of the time it’s not properly mixed as well as it’s distorted. This is because most producers aren’t mixing engineers. When only given the instrumental as a “two-track” in the form of an MP3 or WAV, the engineer does not have control over the individual instruments and layers to cater it to the artist and their vocal. Most of the time this results in the artist's vocals sitting on top of the beat rather than melded with the beat. 

 

Mixing engineers when given an MP3 or WAV of the instrumental can mix the song and we may even be able to mix it very well, but it will not sound as good as it could if the Track-outs, Stems, or Multi-tracks are provided. Any song you’re hearing on the radio or released under a label has been mixed with these and not the “two-track”. This gives the engineer the ability to craft each individual layer to the artist's voice and song to make sure each sliver of audio is perfect. This is how a mix can have dynamics, depth, and width while having that warm low end and top end shine. 

 

Above is the entire process from the rough mix after the recording session, to the mix with the two-track and then the master of a two-track, as well as the comparable mix and master with the multitrack/stems of the same track. This will give you the idea of how big of a deal having the track outs can be to make a record that much better.