After you have done all that you can do in the production of a recording session,it has been concieved,it has been recorded,it has been mixed,you turn up the studio moniters to hear the tune in it's premier state but you are not quite finished.You have got to master it.The final and permanent tweak.some studios may house mastering labs,most do not.If you have come this far does it not make sense to go a couple of extra hundred bucks to etch the tune,to capture that final mix forever?The object you want to send to the pressing plant is not a cd of the final mix to duplicate,or to make available for download sales or streaming,you want to etch it on pure crystal glass.A single speed glass master.Aw sure I know you may scoff at your humble good teacher about this.When I ought to be charging you for this knowledge.I am a very respected scientist in many quarters,this process makes your session "industry standard."this does not mean that it is a major label high dollar session,what it means is no matter how it is heard,through whatever medium known or to become known,it is going to reproduce faithfully the final mix.The final mix enhanced by the maximum EQ levels.The icing upon the wonderful cake.Sure,a great song is a great song but how do you want it to be interpretated by the listener?I am deadly serious about what I do,I don't fuck around with anything.That stuff has got to be right.Even the outakes are mastered.You have already bet your ass on it.For a couple of extra bucks you buy insurance to hedge your bet.The final mix was pumping,champagne flowed in the control room,you had the world by the ass.In the mastering lab you are sitting very quietly,not rocking your head back and forth,the room is sonically designed to the highest spec for listening.Your tech has perfect pristeen hearing and a very strong engineering backround."Creme de la creme."Specialists.They hear everything going down on your final mix.you are hushed,you dare not make a sound.The adjustments to the EQ are milli-second tweaks.You can hear everything that was done on your session.The whole is greater than the sum of all of it's parts.Say for instance on the web,wherever you hear it however it sounds the same.Real bad-ass just like you want it.It jumps up off the tracks!If you do not master your final mix may sound horrific to you on internet radio.If you are really into recording arts and science you find out about "formatting."Now it is mathmatic in three ways,algebraic,plane geometry,and physics.Algebriac in terms of whatever you do to one side of the given equasion you have to equally do to the other.(Stereophonic).Plane geometry,you must set up the appropriate space for what is called "Headroom" plus the ambience of all of the parts.Some frequencies can only hold a limited amount of sound,if you have to many things hogging one frequency "phase cancellation" will occur,the mixing board and recording machine will decide that,which frequency from what it shall pick.And then physics, which is mathematical balance of opposing elements in relation to time and space.For example the setting of the intonation of your guitar is pure physics.why is my instrument in tune in this position and out of tune up an octave?I master my recordings.You ought to do that too.