Your monitoring setup is super important if you are recording music. I would say that it is much less important for voice-over or video narration for a number of reasons, but primarily due to the fact that only your voice is being recorded, which is a pretty simple sound source at a predictable frequency that it doesn't have to share.
With music though, you have multiple sound sources with energy at multiple frequencies, many of which overlap. That means you have instruments (including vocals) often competing for the same frequency real estate. That can cause some sounds to be hidden or masked in a mix. But on top of all of that is the enormous problem of monitoring in a less-than-acoustically-ideal room. Hint: for those of use monitoring music in rectangular rooms, like bedrooms, our monitoring spaces are less-than-ideal by definition. Sound waves coming out of the speakers bounce off the walls and ceilings and collide with other waves. The parallel boundaries (walls, celings, floors) create areas where certain frequencies combine to sound much louder than they really are (yes, the room lies to you!), or do the opposite - make certain frequencies sound much softer than they really are. Sometimes in the latter situation, frequencies disappear altogether!
So imagine mixing in such a room. If bass frequencies are being hyped by the room, and certain middle frequencies are disappearing, you will turn the bass down and the middle frequencies up until they sound "right." But then in a different space, or on an iPod, etc. suddenly the song has no bass at all, and the mids are ripping your sinuses out!
The solution to controlling a monitoring setup is a combination of knowing your mixing room and its tendencies, and doing as much acoustic treatment as you can do reduce the distorting effects of the room. You can also make sure you listen in different spaces to help you get to the "truth" of the mix and then compensate accordingly.
So let's say you have gotten used to your room and maybe treated it as well. You know how to create a good, portable (meaning it will sound good anywhere it's played). But suddenly you either have to move, or mix in an unfamiliar room or studio. That new room will sound strange to your ears. You need to be able to calibrate your ears to that new space.
Here is a great article telling you how to do that quickly by creating your own playlist of songs that you can use to test the acoustic aspects of the new room. They recommend 6-10 songs, each designed to test a different parameter like stereo imaging, dynamic range, 3D imaging, low frequency response, high frequency response, etc.
Read the full article here: