An equalizer or EQ allow you to boost or cut certain frequencies. Some EQ's only have a very few bands, other have more than 10 bands giving you more detailed control.

The most basic EQ is the Graphic Equalizer, where you have a fixed set of sliders each controlling a fixed frequency. You have most like seen one of those on some HiFi equipment.

The Parametric Equalizer give you more control by allowing the user to modify Level (boost or cut), the center of the primary frequency and the bandwidth or range of frequencies.

Ableton EQ Eight is a 8-band equalizer with an integrated real-time spectrum analyzer. By clicking the triangle icon in the upper left corner, the frequency view is enlarged and displayed in the session or arrangement view, which makes it easier to fine tune the EQ settings. In this mode you will also have direct access to controls for all 8 EQ points, which is very useful combined with a MIDI controller. Price: Included in Ableton Live

FabFilter Pro-Q 2 is a professional mixing and mastering EQ with pristine sound and a highly optimized workflow. With integrated spectrum analyzer, where you can graphically modify EQ nodes, EQ Match, Spectrum Grab, Solo mode and much, much more, this will improve your daily work in so many ways.

Neutron from iZotope is a mixing channel strip with EQ, Compressor, Exciter, Transient Shaper and Limiter. The presets and Track Assistant quickly gives you a good starting point and the Masking Meter helps to avoid frequency collisions.

Solid EQ from Native Instruments is a high quality 6-band equalizer with 2 parametric mid-range bands, 2 semi-parametric hi and low bands + hi and low cut. The two mid-range bands are switchable to shelf or bell shape. Available separately or as part of the SOLID MIX SERIES or Komplete 11 and Komplete 11 Ultimate bundles. Price: € 99 or €199 for SOLID MIX SERIES bundled with Solid Bus Comp and Solid Dynamics