Equalization, or EQ for short, means boosting or reducing (attenuating) the levels of different frequencies in a signal.
The most basic type of equalization familiar to most people is the treble/bass control on home audio equipment. The treble control adjusts high frequencies, the bass control adjusts low frequencies. This is adequate for very rudimentary adjustments — it only provides two controls for the entire frequency spectrum, so each control adjusts a fairly wide range of frequencies. Advanced equalization systems provide a fine level of frequency control. The key is to be able to adjust a narrower range of frequencies without affecting neighbouring frequencies.
Equalization is most commonly used to correct signals which sound unnatural. For example, if a sound was recorded in a room which accentuates high frequencies, an equalizer can reduce those frequencies to a more normal level. Equalization can also be used for applications such as making sounds more intelligible and reducing feedback.
There are several common types of equalization, such as:
In shelving equalization, all frequencies above or below a certain point are boosted or attenuated the same amount. This creates a "shelf" in the frequency spectrum.
Bell equalization boosts or attenuates a range of frequencies centred around a certain point. The specified point is affected the most, frequencies further from the point are affected less.
Graphic equalizers provide a very intuitive way to work — separate slider controls for different frequencies are laid out in a way which represents the frequency spectrum. Each slider adjusts one frequency band so the more sliders you have, the more control.
Parametric equalizers use bell equalization, usually with knobs for different frequencies, but have the significant advantage of being able to select which frequency is being adjusted. Parametrics are found on sound mixing consoles and some amplifier units (guitar amps, small PA amps, etc).
Commercial Audio Equalizers
As we know the commercial audio equalizers come packed with lots of features and a very nice casing and with multiple options. Unlike the audio EQ that we can build in our workshops using OpAms and PCBs. Many EQ now a days come with very easy to use interfaces that allow the user to visually set a level and accurately adjust the desired gains.
Graphic equalization is indispensable for response control in a wide range of audio applications. The Yamaha Q2031B delivers professional quality with versatile control and outstanding audio performance. It can be used for live sound, recording, A/V production, electronic musical instruments, broadcasting, music listening, or any other application that requires precise response tailoring. The Q2031B features two independent channels of graphic EQ with full 31-band control over the 20Hz to 20kHz range.
As we can see a commercial EQ is very well presented and ready to use. One of the features that caught our eyes was the part about High Pass Filters. The feature stated: Variable High Pass Filters
High pass filters are useful in minimizing low-end boominess, AC hum, wind noise ... generally preventing subsonic components from muddying the sound as well as wasting amplifier power. The Q2031B incorporates continuously variable high pass filters on both channels, providing 12dB/octave roll-off below any frequency from 20 Hz to 200.
This made a lot of sense to us because when we were designing our Audio Equalizer we were looking into high pass filters to clean the audio signal and have a better quality. In our case this commercial EQ has 31 equalization bands at 1/3 octave intervals from 20Hz to 20KHz. For us it was only to design an EQ with 3 bands. This is the result:
Band Pass Filter Audio Mixer
High Pass Filter...