Effects For Violin: EQ

Overview

Equalization (EQ) is one of the most important tools we have for shaping our sound, but many players don’t understand it. In this article we’ll cover what EQ is and how to use it to make your violin, viola, or cello sound better. We’ll list specific frequencies that are problematic and/or important to have, and we’ll talk about EQ tools such as filters, shelves, roll-offs, parametric EQ, graphic EQ, and which EQ pedals might work best for you.

Frequency

We manipulate EQ by lowering or boosting frequencies (or ranges of frequencies) within our signal. Therefore, it's important to understand a little about frequency.

The frequency of any wave is defined as the number of cycles per unit of time. Visible light waves are perceived as colors based on their frequency. We perceive the lowest frequency (visible) light as red, and the highest frequency (visible) light as violet, with a full range of colors corresponding to every possible frequency in between.

Similarly, sound travels as a wave through a medium (air) at different frequencies. Our ears receive disturbances in the air as vibrations and transmit them to our auditory center in the brain, where they are interpreted as pitch corresponding to their frequency. The smaller the number cycles per second (i.e. the lower the frequency), the lower sounding the pitch. Higher frequency translates to higher sounding pitch.

We use the unit 'Hertz', abbreviated Hz, to denote audio frequency. We further abbreviate frequencies over 1,000 Hz as kilohertz, or kHz. For example, 1,000 Hz = 1 kHz, and 15,500 Hz = 15.5 kHz.

The normal range of human hearing at birth is from 20 Hz to 20 kHz. As we age (and as our ears are overexposed to loud noise) the top range of our hearing deteriorates. Most adults may not hear well, or even at all, above 15 kHz.

Pitch vs. Timbre

Frequencies determine both perceived pitch and timbre, but the two are not the same. The fundamental frequency of a note corresponds to pitch. When an orchestra tunes to 440 Hz, we call that 'A'. Octaves are double or half the fundamental frequency, so the violin and viola's open A is 440 Hz, while the cello's open A is at 220 Hz. The lowest A you can play on a violin E-string is 880 Hz.

Yet when we hear a violin and a viola play the same 440 Hz, we can differentiate between the two sounds, even though they're playing the same pitch. How? Because we can identify the unique character or quality or their sounds, otherwise known as timbre.

What one must understand about musical tone is that a note, as sung played by an instrument, contains not only the frequency that defines its pitch (e.g. A = 440 Hz), known as the 'fundamental', but also many other frequencies above and even below that fundamental frequency. These other frequencies are known as 'partials' and, along with the fundamental add up to form a musical tone with both pitch and timbre.

The timbre is determined by the relative strength of the partials contained in a musical tone. While a violin and viola A may have the same fundamental and all the same partials, some of these partials are stronger or weaker in the violin's A than in the viola's A. The result is timbre and how we can tell which instrument is playing. Every violin has a unique timbre as well, which is how we can tell a Stradivarius from an Amati, or a ZETA from a Viper. That said, the frequency profile of all violins are more similar to each other than to a viola's, making their tones all identifiable to our ear as belong to the timbre category 'violin'.

EQ Explained

Having established that a single musical tone contains a multitude of frequencies working together to relay both pitch and timbre information to the listener, we arrive at the concept of equalization, abbreviated as EQ. EQ is the process of manipulating all the different frequencies to alter the quality of the tone.

Applying EQ to a signal is as much art as science. It requires a trained ear that knows what to listen for, which is what we hope to teach you below. When you hear the sound of your instrument coming through a speaker, you'll have an opinion as to whether it is good or bad sounding. Beyond that, you'll need to understand what is bad about it or, if already good, what could still be improved to make it sound even better, or make it either stand out more or less in a mix. 

Whereas there are a plethora of words to describe different visible light frequencies (the many names we have for different colors), we don't have many that describe sound frequencies. In lieu of precise language, we can do our best to describe the perception of certain ranges of frequencies. This chart shows some frequency ranges with a description of what those ranges add to your tone, as well as cautioning you about what happens if a particular range is too prominent.

EQ Techniques

In applying EQ to your signal, there are a number of ways to manipulate frequency. For starters, you will rarely EQ individual frequencies* but rather you will apply a change to a range of frequencies, known as a bandwidth. These techniques are best visualized using a Real-Time Analyzer (RTA), which you can find in any DAW (Digital Audio Workstation, aka recording software).

An RTA shows all the component frequencies in a signal and their relative amplitude (volume). EQ manipulates the signal by either lowering or raising the amplitude of different frequency ranges, or by cutting them out of the signal completely.

• High Pass / Low Cut aka Low Pass / High Cut

  These techniques do just what they sounds like, and are applied using a 'filter'. A High Pass Filter (HPF, aka Low Cut Filter) allows all frequencies above a certain point to pass through in the signal, which is to say, all frequencies below the set point are cut out of the signal, or blocked from passing. An HPF is applied at the bottom end of the signal. Similarly, a Low Pass/High Cut filter will let you define the highest frequencies to pass, cutting out all higher frequencies from your signal, and is applied at the top end.

  
  
  
  The very first EQ you can and usually should apply to any signal is a HPF. The reason is that sounds below a certain frequency (what Hz depends on the instrument you're playing) are probably unwanted artifacts that aren't contributing positively to your tone, e.g. the thumping of your bow changes. Getting rid of these low frequencies does two things: 1) cleans up your sound, 2) prevents speakers from overworking to reproduce these low frequencies at the expense of the higher ranges that you actually want!
  
  
  Similarly, a LPF that cuts out frequencies at the top end may be useful in cleaning up your sound, but is typically less crucial than applying a HPF at the bottom end.
  
  
  The method for applying an HPF effectively is to set a point below your fundamental frequency and sweep up until you notice a change in sound. At that point, back it down to the highest frequency that does't alter your tone. Remember, the purpose of an HPF isn't so much tone sculpting as it is signal clean-up.
  
  

• Bell Filters

  A bell filter is your most nuanced EQ tool, as it is extremely adjustable. It's called a bell filter because when you apply one to your signal it looks like a bell shape on your RTA. There are three parameters involved in setting a bell filter: center frequency (what Hz the middle of the bell centers on), bandwidth (how wide a range of frequencies fall within the shape of the bell), and amplitude (by how many decibels are your raising or lowering the range for frequencies).

  There's another term you should know, which is 'Q'. Q is the shape of the EQ filter response, as in, how wide and shallow vs. narrow and tall your bell shape is. Q and bandwidth are directly related, in that a higher Q value means a narrower bandwidth with a deeper/taller bell shape, while a lower Q value means a wider bandwidth with a shallower/shorter bell shape.

  When you want to affect a range of frequencies in a way that doesn't sound weird and artificial, you want to use a low Q / wide bandwidth to gentle scoop a wide range of frequencies.

  

  When you want to address a particular problematic frequency--say one that is causing feedback--then you want a high Q / low bandwidth to more surgically remove the offending frequency without much affecting the rest of your tone.

  

   

• Shelf Filters

  A shelf filter boosts or cuts every frequency above or below a given set point. In the example below, a low boost shelf boosts all of the frequencies below 106 Hz while a high cut shelf cuts all frequencies above 4,260 Hz. You'll notice that it's a gradual run up to the flat part of the "shelf" from the set point, as a more abrupt shelf shape would be quite noticeable in the tone. As with bell filters, you can alter the slope of the shelf filter with the Q setting.

  

  
  

Graphic EQ vs. Parametric EQ

Parametric EQ's offer more flexibility and control, in that you can define the center frequency and the width for an EQ band. The EQ plugins you find in DAW (such as in the examples shown above) are total parametric DIs.

Some pedals, while not fully parametric, allow you to tune some ofthe EQ bands to center on a particular frequency, giving you more control. The LR Baggs Para DI and Venue DI both feauture tuning for the mid-range EQ bands.

General Principles For Applying EQ

You may be asking yourself, "when should I use EQ?" The answer is: early and often! There is almost no situation in which you won't want to apply EQ in whatever form it's available to you.

For starters, and before you've added any effects to your signal chain, you'll want to establish your optimal clean tone using EQ. Then, with each stage you add to your signal chain, you'll want to further EQ, since those effects will change your sound. Most effects have a tone control, which is a single-band EQ setting that lets you boost or roll off (usually) the treble end.

If you're working digitally, whether in a DAW or in a mutli-effects software, you'll have even greater control over EQ at every stage. You may find that an effect has added frequencies to your sound that you don't want, in which case you'll need to apply EQ to reduce or eliminate it. In other instances, say with high gain effects, you might get the best result by boosting certain frequencies post-effect.

EQ Strategies

• Before you do anything else, run a High Pass Filter at as high a frequency you can without altering the tone. Remember, this one is about getting rid of unwanted garbage on the bottom end of your signal.Cut unwanted frequencies first. Find offending ranges and gently reduce them to your ear's satisfaction. Notch out any problematic frequencies.
• Cut first, boost last. Subtractive EQ is preferable to additive EQ! If you're trying to get more mids, it's better to cut the lows and highs, leaving a relatively louder mid-range than it is to simply boost mids above lows and highs.
• Use reference recordings. If there's a tone you like and want to emulate, refer to a recording of that sound when sculpting your own EQ. 
• Use an RTA to see the frequencies present in your tone in real-time as you play. Every DAW software comes with and RTA, and you can also download RTA apps for your phone or tablet. This will help greatly in adding a visual reference to what you're hearing, and will result in better training yourself to understand what frequency ranges you're listing to.
• Lastly, be willing to experiement. If you don't know whether cutting a frequency will help or hurt your sound, simply try it! Listen carefully and decide if it's better or worse and why you think so. You'll learn faster and train your ear better by experimenting and noting the results.

Videos