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.
It's Better to Cut
It's a question often asked: is it better to boost or cut using an EQ? Cutting has the desirable property that the resulting phase changes are in the same range as the cut. Any undesirable tonal changes from an EQ cut are therefore reduced compared to a boost where they are amplified. If you are trying to keep your EQ transparent, cutting is a better option than boosting.