Small EQ adjustments create wide curves while larger gain changes create narrower boosts and cuts.ġ5-band, or 2/3 octave graphic EQs, are commonly seen in smaller live sound setups, built into bass and guitar amps, or mounted in studio racks. Some graphic EQs, like the 10-band API 560, use proportional Q technology for a musical response. With the ability to quickly notch out multiple frequencies, 31-band graphic EQs are an excellent choice for live sound applications, where notching out resonances is a necessity. These models typically offer gain adjustments up to 12 or 15 dB. Graphic EQs come in various sizes, including 31-band, 15-band, 10-band, 5-band, and even 3-band.ģ1-band or “1/3 octave” graphic EQs feature 31 center frequencies spaced in 1/3 octave intervals-in other words, three adjacent bands cover the range of one musical octave. Graphic equalizers (like the API 560 graphic EQ pictured below) are simply a collection of fixed-frequency peak/notch filters that can be used to cut or boost several predefined frequency bands at once. That’s why there are so many EQs to choose from. Each brand and model of equalizer chooses design elements that impart a particular color or purity that suits an intended musical purpose. For example, a Chebyshev type filter has a smooth slope the easy-to-implement Butterworth filter may have notable phase nonlinearities the gentle Bessel filter has minimal phase shift artifacts, and the elliptic filter has the steepest filter slope. The sonic characteristics of a filter are based on the type of analog circuit or algorithm that it uses. They’re built into instruments, amplifiers, and equalizers and are used by everyone from musicians to mastering engineers. Notice that each slope crosses 100 Hz at the same level, even with their different slopes.įilters are used in almost every stage of audio processing. This diagram displays three different slopes of 6dB, 12dB, and 24dB per octave. A filter’s corner frequency, referred to as the -3dB point, indicates the point where the filter has attenuated the level by 3dB. Some advanced filter designs create a resonance peak (boost) right at the cutoff point for a little emphasis at the cutoff frequency.įILTER SLOPE. Most analog filters have slopes of between 6dB and 24dB per octave, with higher numbers correlating to steeper slopes. The slope of a filter describes the shape of the transition between the filtered frequencies and the passed frequencies. Band-pass filters can create effects like the sound of a cell phone speaker, while notch filters can remove ground buzz or other resonant frequencies. The opposite of a band-pass filter is a band-rejection filter, also known as a notch filter, which removes a narrow frequency band and leaves most of the signal unaltered. High-pass filters on microphone channels can remove low-frequency rumble from air conditioning, trucks driving by the studio, or bass that bleeds through the control wall into the vocal booth.īand-pass filters remove the content both above and below the center frequency, allowing only the audio around the center frequency to be heard. Alternatively, low-pass filters block frequencies above a selected point, attenuating the highs and allowing the lows to pass through. High-pass filters, for instance, cut all the frequencies below a selected point, attenuating the low frequencies and allowing the high frequencies to pass through. In this article, we will mainly discuss “pass” type filters, which only allow certain frequencies to come through while rejecting everything else. Filters are commonly thought of for removing unwanted elements, but a filter is more technically any single frequency band of an equalizer. Generally speaking, a filter is any device or circuit that changes the tone, or timbre of an audio signal by amplifying or attenuating a range of frequencies. Filtersįilters are considered one of the basic building blocks of signal processing. We will also explain the role that each type of EQ plays as part of your audio toolbox. In this article, we’ll break down everything you need to know about filters, graphic EQs, parametric EQs, linear-phase EQs, and dynamic EQs. When it comes to tools of the trade, the equalizer is easily the most important signal processor in any audio engineer’s arsenal, and to use EQs properly, we need to understand how all the different types of equalizers work.
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