If you find it difficult to get a song sounding right when you come to mix it, you are not alone. Left to their own devices, many instruments used today tend to congregate in that busy 200Hz to 500Hz region of the audio spectrum, contributing to a muddy-sounding track, and many people discover the clutter too late in the game, at the mixing stage. Although it's true that EQ can be used to shave off excessive high and/or low end from individual tracks (a popular technique known as 'bracketing'), this has its limitations and can't always sort out problems originating from the very earliest stages of development, when the song was being arranged.
Modern instruments are capable of covering a very wide audio spectrum, creating sounds with rich harmonic structures that can make placing them in a mix with other instruments difficult. By contrast, acoustic instruments that have evolved to play in recognised ensembles such as orchestras and traditional ethnic music groups tend to occupy their own part of the audio spectrum, not overlapping too much with the other instruments in the ensemble.
In an orchestra, for example, only those instruments that are used for playing bass parts tend to generate much in the way of serious low end (basses and timpani being obvious examples). Violins and violas have no low end to speak of, and even their incursion into the lower reaches of the mid-range is very limited. Likewise, the oboe stays tidily above the lower mid-range mudbath, while the high-end instruments, such as triangles, piccolos and cymbals, typically play only when they're needed.
Looking at modern instrumental offerings, we come across the synthesizer, a wonderful invention that has fascinated me since I first heard one in the late '60s. But its flexibility is also its curse. When you look at the orchestra, most of its elements are monophonic, or duophonic at most, whereas a synth allows you to play a fistful of wide-frequency notes. Furthermore, most synths come loaded with exciting presets that help them sound good when you try them out in isolation, but many of these sounds are too dense to use in a practical arrangement. So you need to create your own patches, which might, when played on their own, seem less exciting than the stock presets.
The electric guitar has problems similar to those associated with the synthesizer; once you've added a bit of overdrive, the total range from deep cabinet thump to to upper-mid grind can take up lots of sonic real-estate, a situation compounded by the extra sustain that comes with distortion.
But what of the piano which, despite its age, is still omnipresent in music these days? Well, although it covers a wide musical range, the notes themselves leave plenty of spectral space around them and between their harmonics, while the naturally decaying envelope of the sound helps to create space.
Though the line-ups afforded by modern instruments, such as guitar, vocal, bass and drums in a rock band, are established, there's really no standard way that the instruments should sound, unlike with an orchestra, so it is up to the arranger to make sure that all the instrument sounds and their playing dynamics fit together like a jigsaw, rather than obscuring each other. Just remember, the more planning you do when choosing sounds, the less remedial work you'll be left with when you come to mix.
Paul White Editor In Chief