A parametric equalizer (parametric EQ, or EQ) is one of the specialized filters provided by Audio Toolbox™ for audio signal processing. It is typically a cascade of independently tunable filters used to alter the spectrum response characteristics of the original sound by cutting (gain attenuation) or boosting (gain increase) specific frequency bands in real time with MATLAB^® and Simulink^®.

In practice, several parametric equalizers are cascaded and used simultaneously to equalize an audio signal. A parametric equalizer is one of the widely used audio filters in audio systems and audio plugin in digital audio workstations (DAWs) for altering, blending, or correcting sound or music.

For example, the parametric equalizer:

• Enhances the listening experience by finely adjusting specific frequency bands to improve a particular musical instrument sound coming out of smartphone or MP3 player headphones, home stereo speakers, or car stereos
• Enables control of multiple key filter parameters individually to alter the overall frequency response characteristics of multichannel streaming audio
• Provides control for peak gain, central frequency, and bandwidth (quality factor) over a wide range of frequencies

Audio Toolbox and DSP System Toolbox provide many algorithms and specialized filter design techniques to quickly design, implement, and analyze tunable multiband parametric equalizers in MATLAB or Simulink. Depending on the audio filter constraints, you can design second-order or high-order IIR filters, which provide much more control over the shape of the filter by yielding sharper transition bands for the same bandwidth gain. For the design process, you can use various criteria ranging from quality factor to octave bandwidth constraints, using many filter types including low shelving and high shelving filters, and peaking and notching filters.

If you design an equalizer or another audio processing algorithm using MATLAB, you can use Audio Toolbox to convert it into a VST plugin to run it natively in an external DAW. Alternatively, if you already own an equalization algorithm as a VST plugin, you can host it in MATLAB and control it programmatically like a regular object to process MATLAB arrays.

Left: Examples of magnitude responses commonly used for signal equalization. Top right: A custom implementation of a three-band parametric equalizer tested in real time using the Audio Test Bench app. Bottom right: A VST plugin generated from a MATLAB authored parametric equalizer, as seen from REAPER, a third-party DAW.