In theory, the same individual sonic results can be be achieved through additive EQ as subtractive. There is the issue that boosting is in effect adding gain and potentially noise to a sound- which is why a lot of engineers (especially monitor and systems engineers) stick to using the latter. Aside from this even if these things aren’t an issue in a given situation we generally stick to one system or the other.
I have recently adopted a predominately subtractive model- for reasons that are not technical. The decision was prompted by a question that I asked myself one day as I was stood at Front of House: “what is my thought process and motive for what I am doing here?” If we are boosting a frequency, I think we need to be careful that we aren’t trying to add more than a sound contains; unnaturally over exaggerating fundamentals which should naturally be prominent. I think there is a massive difference in choosing to make an additive boost or instead using a subtractive approach. The difference in sound quality we can technically achieve is minimal and this is not what I’m talking about here. When shaping a mix I used to loved the process of additive EQ simply because I believed it was more creativley effective than its subtractive counterpart: adding more and more to the foundation of a sound to create the aural landscape I had in mind.
Now my belief is that the sound I am mentally visualising, as I stand at the desk, has always been there in reality, and to get there, what I really need to do is carve it out; destroying impurities created by the room, electronics, acoustics, harmonics and standing waves etc. Look again at the EQ curve above. Do you immediately see the EQ as the coloured mass sinking downwards or do you see the emergence of three smooth black peaks? The Italian renaissance artist and architect Michalengo famously quoted:
“Every block of stone has a statue inside it and it is the task of the sculptor to discover it.”
My belief is that subtractive processing is an advanced technique not because it is technically difficult; but because it comes from a wholly different belief system. I think sometimes it’s good to remember that the gift we have been given in music and sound is not created by us. We cannot create sound itself. At best we generate it from an instrument, our vocal chords or from some form of computer. I think we would find so much joy and effectiveness by realising that we are stewards of this amazing gift given to us and use that as the basis of our creativity. Our realisation of the sound that we envision already awaits us to be chiselled out; creating in us a tenacity to strive for mixes that we discover are sonically possible.