Any single one of these qualities can be achieved easily. The problems begin when a client of the professional mixing service demands all these qualities to be present together. Of course, active using of reverberation, chorus, pitch shifter and other effects will lead to an increase in base width and space of the song. However, it also means that transparency and density will be lost. Too much space processing will cause sound to be incoherent and blurred. And if you remove spacing effects, you will improve instruments’ audibility with the expense of audio spaciousness.
These problems can only be solved as a whole. During mixing and mastering, you should imagine yourself both as an artist and as a sculptor. How does sculptor work? He takes a rock and cuts off extra parts. That’s exactly what an audio engineer should do when mixing a song. Let’s consider an example. You have two parts playing simultaneously: strings play the rhythm and the pad flows in the background. Strings’ audibility is usually determined by a frequency range of 2 to 4 kHz. In that case this part of spectrum has to be free of the pad (its part must be lower than 2 kHz).
Another example: higher part of spectrum is usually occupied by hats, shakers and other percussion instruments. When arrangers choose sounds, they usually follow their own taste, ignoring compatibility of instruments. In order to solve this problem, a mixing engineer needs to spread instruments all over the spectrum. For example, hi-hats should be lifted up to 6…8 kHz, the shaker should be lowered to 2…4 kHz and the tambourine will be great in the middle of them. All of the above applies to other instruments as well.
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