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3 comments / Posted by Bruce Ohms

High Shelving, Low Shelving Graphic EQ

It is highly unusual to come across any sound system that lacks some form of equalization. While many features are only on the fanciest and most expensive systems, EQ is just about everywhere. Yet of all processing equipment equalization is one of the least understood and most underestimated by everyday musicians. It’s not surprising with all the strange terms used to describe these versatile and powerful tools: from high shelving to low-pass, parametric, semi-parametric, quasi-parametric, bandwidth, “Q”, notch-filters, etc., -sounds like sci-fi movie term. At first glance these tools can seem a little bland and unexciting, but knowing how they work can mean the difference between music that sounds lackluster (or terrible) and music that sounds so good it comes to life. We’re going to take a tour of the world of EQ and by the time we’re finished you’ll hopefully approach equalization with more precision and confidence. But first we need to understand a little about frequencies- these odd and invisible little ‘things’ that are so important to capturing great sound.

When we talk about frequencies we often refer to how “high” or “low” they are.
In general terms this refers to the period of the waveform. The shorter the period of the wave, the faster it cycles, and the higher it sounds to our ears. We commonly talk about the frequency of the waveform in Hz, or cycles per second. But music is rarely as simple as a single waveform; when we listen to music we are hearing many waveforms all at once. Even a single instrument playing only one note typically produces multiple frequencies, something we call ‘harmonics.’ When you play a middle-C or an A-440 you hear more than just that single frequency (called the fundamental) but you are also hearing many other frequencies (called harmonics) at varying levels usually much lower than the fundamental frequency. It is this layering of additional notes which create the distinctive timbre of each instrument, acoustic or electric. The decidedly ‘clean’ sound of a flute is due to the very small number of additional harmonics it creates (and how low their volume level is) so you mostly hear just the fundamental. Each instrument has a different collection of prominent harmonics. Modern electric bass tone with lots of upper midrange character is loaded with harmonics, as are the complex distortion sounds most rock guitarists choose. This means being able to control the level of the various harmonics allows a very great degree of control of the overall sound. If your amp sounds “too fuzzy” it might be due to having your high frequency EQ adjusted incorrectly, and judicious use of EQ can also help make an amp “pop” out of or “blend into” the mix. An equalizer is just a way of sorting these frequencies into groups so we can adjust how loud or soft they are. The more sophisticated the EQ system is, the more precision and accuracy we have to select narrow groups (or bands) of frequencies, but also the more complicated and time-consuming it is to adjust in a practical situation (which is why nearly every Carvin Audio bass amp offers the same combination EQ section as our BX1600).

BX1600 Bass Amp Head with Combination EQ

BX1600 Bass Amp Head with EQ

We started off wondering what is meant by ‘high-shelving’ and ‘low-shelving’ EQs and these are the most basic and common types in use (also called ‘treble’ and ‘bass’ respectively). The filter allows all frequencies beyond a pre-selected point to ‘pass’ while attenuating the rest. A graphic representation of the EQ curve resembles a ‘shelf,’ hence the name. While these basic EQs are easy to operate and allow you to tailor the overall sound, they don’t allow more precise adjustments, which is where all the various types of equalizers come in. Once you begin to see how effective each of these EQs can be, you’ll begin to know intuitively which type EQ will help you achieve the sound you’re looking for the fastest.

In Part Two of this series we explore the different types of equalizers and how you can use them to take your sound to a whole new level.


  • Posted On February 24, 2017 by Bernie Hynson, Jr

    Excellent article on “Shelving”. The “High End” quality of your products, demands such ‘quality’ articles (shelving) to be a regular appearance on your web page. Bravo! Let the rest buy from the neighborhood music store.

  • Posted On February 24, 2017 by Steve Luster

    Very helpful. A recording engineer was trying to explain this to me after I’d complained that my bass sounded very flat, and was difficult to hear in the mix. I’m very much looking forward to part 2.

  • Posted On February 24, 2017 by Claude Hitt

    I’m always struggling on stage with my sound . One sound doesn’t fit for all songs . For me . The article helps . I have to get my EQ working for me ..,

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