Understanding the Audio EQ Tool

By in Video Editing

Hello, my name is Benjamin Hershleder and this is my second contribution to the Avid Blogs. I recently had a book about Media Composer editing published. However, the publisher had a page count limit for the book, which meant that some entries had to be left out. Not one to let things go to waste, below is an “outtake” that provides an overview of the EQ Tool.

Now, this isn’t going to be an entire section on everything about sound. I’ll leave that to the experts. But what I can do is give you a general understanding of what the EQ Tool is allowing you to adjust. But that means giving you a bit of background on a few things before we get to the tool.

Frequency Basics Overview

Equalization (“EQ” for short) is essentially reducing or increasing the volume level of certain frequencies in an audio signal to make them less prominent or more prominent (quieter or louder). What is a frequency? Well, that term refers to how many regular fluctuations (a.k.a. “oscillations”) of a sound wave occur during one second. If there are very few waves per second (a low frequency), then the sound is a low note. If there are a lot of waves per second (a high frequency), then the sound is a high note.

Anything that occurs at a regular rate (a number of “somethings” happening in one second) can also be described as a cycle. For example, a piston in your engine moving up and down does this a specific number of times each second, in other words in cycles. Each sound wave can also be described as a cycle. It has a beginning, a middle and an end; and then it repeats again, and again, and again. However, when we talk about sound, we generally don’t say “Waves per second” or “Cycles per second.” Instead, we use the term Hertz (abbreviated as Hz), which is named after the German physicist Heinrich Hertz. For emphasis: “Cycles per second” and Hertz are the same thing. Hertz are used to describe various phenomena that occur at a regular rate. You’ve likely heard the term Hertz used before to describe electricity (e.g. 50 Hz or 60 Hz), and I imagine you’ve heard it used to describe the processing speed of a computer (e.g. 3 GHz). Computers are so fast today that we don’t relate the speed in terms of just Hertz, but instead in terms of billions of Hertz, which are called Gigahertz (abbreviated as GHz). OK, let’s get back to sound. Below is an animated picture of sound wave frequency in one second, and you can see in the top right of the image (below) how the number of Hz increases as the number of waves increases.

Source credit: Image from Wikipedia – http://en.wikipedia.org/wiki/File:Wave_frequency.gif

Remember that in sound, the greater the Hertz, then the higher the note. Essentially, people can hear very low frequencies starting at about 20 Hz and as high up as around 20,000 Hz (a.k.a. 20 Kilohertz, which is abbreviated as 20 kHz). The bad news is that, generally, the older you get the less frequencies you can hear, with the most noticeable loss being in the high frequencies. So, the average middle-aged adult can generally hear frequencies between approximately 60 Hz and 17,000 Hz (a.k.a. 17 kHz). If you’d like to unscientifically test out your own hearing range, then stop by this web page: http://www.egopont.com/hearing_tests.php (Mac users may be prompted to install the Flip4Mac plug-in).

It’s also helpful to know where human speech falls on the frequency spectrum. Adult men generally have speech that ranges from approximately 80 Hz to 180 Hz, while adult women generally have speech that ranges from approximately 160 Hz to 260 Hz.

Demystifying The EQ Tool

If you have your Media Composer or Symphony in front of you, I’d encourage you to fiddle with the tool as I go through the overview. I think it will help some things to make a bit more sense. The EQ Tool can be found here: Tools Menu > Audio EQ Tool.

Media Composer’s standard EQ Tool is what is referred to as a “Three Band Equalizer.” This means that it can affect three bands, or sections, of the audio frequency spectrum. You can think of bands as ranges of frequencies across the audio frequency spectrum starting at 0 Hz up to 20 kHz. The more bands you have available to tweak, the more control you have over specific frequencies. For example, one of the plug-ins available in the AudioSuite (Tools Menu > AudioSuite) provides 7 bands of EQ adjustment.

Below are some basics to help demystify the Audio EQ Tool.

A – EQ Effect Icon: Drag this to any open bin to create an Effect Template that can be applied to Segments in the future.

B – Audio Loop Play Button: You can make adjustments while Media Composer loops. To do this, Mark In/Out for a portion of a Segment, one Segment, or multiple Segments. Then press the Audio Loop Play button. Make adjustments during the loop. Note that the changes will not be applied until the loop cycles back to the beginning. For this reason, you may find that selections of short durations work the best. Stop the looping playback by clicking the Audio Loop Play button. Any adjustments made during the audio looping will be applied.

C – Render Effect Button: If you make adjustments to an EQ Effect that you previously rendered then it may need to be re-rendered. You can use any render method; this button is provided as a convenience.

D – EQ Tool Fast Menu:

  • Provides various functions to more efficiently add and remove multiple EQ effects to tracks that are enabled. These functions can affect an entire track (“Global”, meaning that there are no marks on the track) or to just the segments that are between an In-Mark and an Out-Mark (“I/O”).
  • Provides a variety of EQ Presets. Once a preset is selected it is applied to the Segment(s) on the enabled track(s). These preset templates cannot be modified. The presets include:
  • NTSC and PAL Hum Busters: Reduces the hum that can occur when audio cables are placed too close to electrical cables during production. This preset template targets (a.k.a. “Notches”) specific frequencies and reduces them.
  • Tape Hiss Filter: Targets high frequencies, starting at approximately 12 kHz, and reduces them.
  • Telephone EQ “A” and “B”: The two presets boost and reduce a variety of frequencies to emulate how a person may sound when heard over the telephone. These are also useful to make audio sound as if it is coming out of an old radio.

E – Track Selector Menu. Use this menu to target one or more tracks in the Timeline for an EQ effect. To target multiple tracks, using this menu, you would use the Shift key. Alternately, you can enable/disable the Track Selectors in the Timeline to target which tracks’ segments get the EQ effect.

F – Decibel (dB) Level Display. There is one of these displays for each EQ “Band” Slider.

G – Bypass Real Time EQ: Note that this does not apply to EQ effects that have been rendered. Avid states, “Lets you instruct the system to ignore all the EQ effects. This button is also available in the Audio Mixer tool and the Output tab in the Audio Project Settings dialog box. If you select this feature in one place, it is selected in the others as well.”

H – IN Button: “In” is an abbreviation for “Inline.” This lets you enable or disable the current EQ effect. When the button is yellow, the effect is enabled.

I – Low Shelf: Rather than using the Audio Mixer to make all the frequencies in the audio signal louder or quieter, this is essentially allowing you to affect just the lower frequencies as dictated in the Low Shelf Turnover Point Menu (see letter “L”).

J – Parametric Midrange: Rather than using the Audio Mixer to make all the frequencies in the audio signal louder or softer, this is essentially allowing you to affect just the frequencies in the middle of a range of frequencies you dictate by using the Parametric Midrange Turnover Point Menu (see letter “M”) in conjunction with the EQ Range Slider (see letter “O”).

K – High Shelf: Rather than using the Audio Mixer to make all the frequencies in the audio signal louder or quieter, this is essentially allowing you to affect just the high frequencies as dictated in the High Shelf Turnover Point Menu (see letter “N”).

Definition of Turnover Point for letters L, M, and N:

Avid’s Help document relates, “A turnover point is the point at which the curve [in the display graph – see letter “P” below] starts to return to 0.” The three menus discussed below (letters L, M, and N) allow you to adjust the Turnover Point for each EQ Band. This is essentially allowing you to instruct Media Composer what range of frequencies you want to affect.

L – Low Shelf Turnover Point Menu: Selections are 50 Hz, 80 Hz, 120 Hz, and 240 Hz. If you select 50 Hz, then you are affecting fewer frequencies (50 Hz and below). If you select 240 Hz, then you are affecting many more frequencies (240 Hz and below).

M – Parametric Midrange Turnover Point Menu: Selections are 2 Octaves and 1/4 Octave. You use the EQ Range Slider (letter “O”) to select a center-point of frequencies you want to affect. When you set the menu to “2 Oct” you are affecting frequencies 1 Octave on either side of the center-point you’ve chosen. When you set the menu to “1/4 Oct” you are affecting frequencies just 1/8 Octave on either side of the center-point you’ve chosen. The 1/4 Oct setting is useful for isolating a small area of frequencies in order to boost or reduce them. To do this:

  1. Start by setting the Midrange Slider (letter “J”) to its loudest value (+15).
  2. Mark In/Out around a few seconds of audio (short durations, approximately 2 to 5 seconds, work best).
  3. Press the Audio Play Loop Button (letter “B”).
  4. Adjust the EQ Range Slider (letter “O”).
  5. Allow the blue Position Indicator to cycle back to the beginning of the region you’ve marked in order to hear the adjustment take affect.
  6. Once you’ve located the specific range of frequencies you want to affect, you will adjust the Midrange Slider to a value that works best for your needs.

N – High Shelf Turnover Point Menu: Selections are 6 kHz, 8 kHz, 12 kHz, and 15 kHz. If you select 15 kHz, then you are affecting fewer frequencies (15 kHz and above). If you select 6 kHz, then you are affecting many more frequencies (6 kHz and above).

O – EQ Range Slider: This is used together with the Parametric Midrange Slider (letter “J”) and the Parametric Midrange Turnover Point Menu (letter “M”). It allows you to adjust the center-point of the parametric curve by adjusting the slider left and right along the audio frequency spectrum (low frequencies on the left, high frequencies on the right).

P – EQ Adjustment Display Graph (Avid calls it the EQ Parameter Graph): Provides you with a visual representation of which frequencies you are affecting, how you’re affecting them (boosting or reducing), and how much you are affecting them. This is a display only. It is not interactive.

I hope this overview was helpful in demystifying the EQ Tool. I also encourage you to take advantage of all the explanations, tips, tricks, and step-by-step help offered in my book Avid Media Composer Cookbook.

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Benjamin Hershleder has been an Avid Certified instructor since 1997, and is the author of "Avid Media Composer Cookbook". He provides private Avid training in addition to being a freelance editor and director, as well as an adjunct professor at American Film Institute in Los Angeles.