When you boost or cut your audio using an EQ there's more going on to the signal than just increasing or decreasing the gain at chosen parts of the audio spectrum. This article explains what happens to your precious sound when you boost or cut so you can apply your EQ with expert care.
A Closer Look at an EQ Boost
The following diagram shows the decibel gain and phase response of an analog EQ boost:
The EQ boost of 5dB centered around 500Hz is causing a phase change in the audio which is also centered around 500Hz. This phase change mostly affects the frequencies between 100Hz and 1kHz imparting a slight tonal change in the overall audio. The EQ boost further amplifies this tonal change.
A Closer Look at an EQ Cut
The following diagram shows an equivalent analog EQ cut:
This EQ cut is the opposite magnitude and same center frequency as the boost above. It introduces an equivalent phase change (albeit a mirror image). This time, however, the EQ cut is reducing the effect of this tonal change.
This article illustrates the equal and opposite phase changes that occur around the center frequency of a cut vs a boost and highlights that boosting makes these phase changes more noticeable. It takes a different mindset to apply a cut if you are used to boosting. The opposite of a boost is not to apply cuts to achieve the same overall shape, but to tackle issues such as auditory masking where instead of boosting a frequency, you look to make a cut in a competing frequency range (which may be a different track to the one you are trying to make room for) so that the frequencies you are interested in become more discernible.