So you find it easy to isolate musical instruments with different frequency characteristics. For example if the mix is only consist of a simple vocal and a bass guitar; then even without any effects the vocal and the bass would stand out naturally because they are occupying completely different frequency characteristics.
As you might know, vocals frequencies are common around 300Hz to 3000Hz while bass guitar obviously occupies below 200Hz; so finding space for them in the mix is not really a serious problem. But what about you have two or more instruments in the mix having the same frequency characteristics? This is where you can see a lot of challenges in the audio mixing process because it is becoming hard to isolate them properly in the mix.
The following are very common audio mixing issues:
1.) Vocals vs. the Background vocals – particularly if the lead and background vocals are both female or both male. But in case of a male lead singer with female background vocals or vice versa; it won’t be a serious problem since female voices tends to occupy at a higher range of vocal spectrum.
2.) Kick drum and bass guitar – this is often a common source of audio mixing issues.
3.) Guitar vs. Vocals vs. Other string or wind instruments (violin, flute, etc.) – these instruments have the same frequency characteristics, becoming harder for them to isolate properly in the mix.
Effects that you can use to improve clarity and space in the mix
For best results, you would be using the following effects:
1.) Parametric EQ –Basically the principle is that; supposing two instruments sound the same (or occupying the same frequency spectrum); you can use EQ to make them sound different in the mix. This is done by applying the concept of “contrasting EQ”. This works by boosting a certain frequency range favoured for that first instrument for clarity/definition and then cutting that same frequency range on the second instrument. Make sure that the amount of cut and boost are in the same values but in opposing direction. The Q should be the same as well. See an example EQ setting of two instruments occupying the same frequency spectrum applied with “contrasting EQ” effect:
First instrument: Boost +6dB 400Hz at Q=1.4, Cut -3dB 2000Hz at Q=1.0, Cut -3dB 8000Hz at Q=1.4
Second instrument: Cut -6dB 400Hz at Q=1.4, Boost +3dB 2000Hz at Q=1.0, Boost +3dB 8000Hz at Q=1.4