Introduction to Music Production 3 – EQ
Some more background information on Frequency before we dive into the world of EQ!
Frequency, as stated before, is exponential with regard to pitch.
A sine wave is the only ‘pure’ wave shape that produces only the frequency in which it is being oscillated (called the fundamental frequency). Other wave shapes produce more frequencies higher (and sometimes lower) than the fundamental frequency, called partials.
Partials consist of harmonics and inharmonic frequencies. The partials give a sound it’s timbre (character). For instance, a guitar and a piano can share the same fundamental frequency, but since they have different partials, they produce two totally different timbres.
To find the harmonic series, take the original frequency and multiply it by the increment of the harmonic. For instance, A4 is 440 Hz. The first harmonic is the fundamental frequency, 440 Hz. The second is 880 Hz, third is 1320 Hz, fourth is 1760 Hz, fifth is 2200 Hz, sixth is 2640 Hz, seventh is 3080 Hz, and so on. This series does not include all of the partials that exist for every sound, but harmonics are a very important part.
Here is an audio clip of a sine wave playing the harmonic series starting at A4.
In digital synthesis, inharmonic partials are largely determined by the shape of the wave(s) being oscillated. In physical instruments, those partials are determined by factors such as the shape and size of the instrument, medium of vibration (the natural oscillator), material of the instrument, and other factors.
An octave, an increment discussed often in music theory, is simply double the fundamental frequency. For instance, A4 is 440 Hz. A5 is 880 Hz, A6 is 1760 Hz, A3 is 220 Hz.
Here is an audio clip of a sine wave playing octaves starting at A3 – 220 Hz.
Now for EQ!
What is Equalization (EQ)? Equalization is the process of adjusting the balance between frequency components within an electronic signal. How does this help in production? It creates space in your mix of instruments by taking out unnecessary frequencies, and helps balance the overall timbre of each instrument.
Frequency – The amount of times a wave oscillates per second, measured in hertz or Hz. Frequency determines pitch. Higher frequency = higher pitch. Lower frequency = lower pitch.
Bandwidth: the range of frequencies within a band.
Q = Frequency/Bandwidth (Frequency divided by bandwidth). This value determines the width of a point on an EQ, as Frequency relative to pitch is exponential, and bandwidth needs to be scaled. Higher Q means smaller band, Lower Q means wider band.
Gain – used to boost or cut volume, measured in dB.
EQ is used to shape the timbre of sounds by boosting and attenuating (cutting) frequencies. There are a few shapes associated with EQs that are crucial for understanding how it all works. Note: Most EQs read frequencies from left to right, where the left side contains lower frequencies, and the right contains higher frequencies.
Low Pass (High Cut) & High Pass (Low Cut) Filter – Low Pass (High Cut) removes frequencies above the set frequency. High Pass (Low Cut) removes frequencies below the set frequency. Lower poles (i.e. -6 dB) give a smoother cutoff, higher poles (i.e. -30 dB) gives a sharper cutoff. The Q can also somewhat alter the smoothness of the curve, but can also introduce resonance around the set frequency. The high pass filter is on the left in the photo, and the low pass is on the right.
Low and High Shelf – Shelves boost or cut every frequency above (high) or below (low) a set frequency. The Q on a shelf determines its shape. The low shelf is on the left in the photo, and the high is on the right.
Bell Curve – the set frequency is at the center of the curve, and the Q determines the bandwidth. Bell curves are used to boost and cut frequency ranges.
Notch Filter – the set frequency of a notch filter is at the center of the notch. Notch filters are used to cut frequency bands, where the maximum attenuation (cut) is at the set frequency, and the Q determines bandwidth and the slope of frequencies on either side.
Band Pass Filter – A bandpass filter’s highest point is at the set frequency, and frequencies on either side are progressively attenuated (cut). The Q of a bandpass determines the bandwidth and the slope of attenuation on either side of the set frequency.
Personally, I practice a type of EQing called subtractive equalization. The premise is that you carve out a specific frequency space for each instrument by using high and low pass filters. For instance, if you record a vocalist, you may find inaudible, but existing frequencies under 200Hz. For this, you could use a high pass (low cut) filter around 200Hz to remove the unnecessary information. Even though you may not be able to hear that information, it could potentially muddy up the lower frequencies in your mix. I frequently put an EQ on every sound with a high pass and a low pass to remove any sounds outside of the instrument’s range.
In addition to using high and low pass filters to remove unwanted frequencies, I find that when I need more of a frequency of a sound, it is smoother to reduce the other frequencies instead, or to EQ another instrument differently to let the first shine through. Boosting EQs over 6 dB can sometimes cause unwanted digital distortion by means of artifacts.
Don’t forget to use your ears! It’s good to understand what the numbers mean/do, but mixing by numbers will never have an end result as good as your ears.