The recording engineer uses "EQ" to adjust for microphone placement and overpowering frequencies. In any drum microphone setup, certain frequencies can overwhelm others. For example, the attack of the cymbals may drown out the attack of the snare. With proper EQ application, the engineer can balance the competing frequencies. Engineers also use EQ as a way to make the drums fit into the rest of the song. If the drums may overwhelm the other parts, the engineer adjusts the frequencies until it sits perfectly in the song.
Every drum kit causes undesired noises, such as ringing snare drums, squeaky drum pedals and creaky drum thrones. A noise gate cuts out these undesirable sounds. The noise gate works as a cut-off switch. It allows a signal through until it drops below a certain threshold, at which point the noise gate cuts the signal. When the signal rises above the threshold, the noise gate opens. By setting the threshold to cut off the unwanted noise, only the drum signal is heard.
Compression levels out the drum track by bringing up the softest sounds to match the loudest sounds. For drummers with inconsistent hits, compression can save a drum track from being lost in the mix. Careful use of light compression gives snares and tom-toms more sonic space in the drum track without competing with the kick drum's frequencies. Compression comes with two dangers, though. First, it can kill the attack of the kick and the cymbals. Second, a compressed track cannot be uncompressed.
Reverb simulates room acoustics. This allows the recording engineer to provide the correct atmosphere for the song. It also allows certain production tricks to make drum kits sound better. A technique called "gated reverb," first popularized by producers Peter McIan and Hugh Padgham in the early 1980s, provides an explosive quality to snare drums. Reverb also allows producers to create a wash-out effect on specific drums. The technique creates dreamy, atmospheric drum sounds.