What is comb filtering? How does comb filtering affect sound quality? What causes comb filtering? All of these questions are answered in this video. This video contains demonstrations that show the various causes of comb filtering. You'll hear for yourself how phase cancellation can change the sound quality of a recording.

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0:00 - Intro
0:21 - What is Comb Filtering?
0:36 - The Basics of Phase Interference
1:00 - Time Delay & Comb Filtering
2:01 - Comb Filtering of a Voice Recording
2:21 - What Causes Comb Filtering in the Physical World?
3:50 - Subscribe to Audio University!

Read the article I wrote about comb filtering here for more information: https://audiouniversityonline.com/comb-filtering-explained/

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In this video, you'll learn about comb filtering.

I'll explain how it works, and I'll give you practical examples so that you can see and hear it for yourself.

My name is Kyle, and I've created Audio University to help you learn the fundamental concepts of audio and how to apply them.

If that sounds interesting, subscribe below.

Comb filtering occurs when 2 or more identical audio signals are mixed together at a slight delay.

The resulting frequency graph of these signals resembles a comb, hence the name comb filtering.

To understand comb filtering, it's first important to understand the basics of phase interference.

These 2 audio waves are identical and perfectly in sync or in phase.

They add together to create a bigger wave.

These 2 audio signals are also identical, but they're perfectly out of sync or out of phase.

In addition to waves being perfectly in phase and perfectly out of phase, waves can be slightly out of phase to varying degrees.

Here's what a wave like this would look like on a frequency graph.

Most sounds, however, are made up of many frequencies.

Here's a frequency graph of white noise which contains all frequencies.

Let's pretend that these tracks are the various frequencies and white noise.

I'll copy these frequencies and paste them below.

Now there are 2 copies of each frequency.

When the audio clips are in sync, all of the frequencies are in phase.

However, when I shift all of them by just 1 millisecond, look what happens.

Some frequencies are still in phase, Some frequencies are slightly out of phase, and some frequencies are completely out of phase.

Some frequencies will add together, some will cancel out, and that forms a comb on a frequency graph.

My voice is also made up of thousands of frequencies.

Here's what my voice looks like on a frequency graph.

Listen to the effect that even a slight delay can have on the sound of my voice.

There are 3 main causes of comb filtering in the real world.

Reflections, multiple speakers, and multiple microphones.

Let's start with comb filtering caused by reflections.

The sound from this speaker takes 2 paths to the microphone.

A direct path from speaker to microphone and a reflected path from speaker to wall to microphone.

The reflected sound travels a longer distance and will reach the microphone slightly later than the direct sound.

Listen to the way the comb filter changes based on how far away the wall is from the speaker.

Another cause of comb filtering is multiple speakers.

The sound from the left speaker reaches the microphone before the sound from the right speaker.

The sound changes depending on which speaker is closest to you.

And finally, comb filtering can occur when you're using multiple microphones.

Listen to the way the sound changes as the distance changes when I mix the sound from each microphone together.

In future videos, we'll take a look at how to avoid phase cancellation and comb filtering, but we'll also take a look at how phase cancellation can be harnessed in technology.

If you got value out of this video, click the like button, subscribe to Audio University, and check out the website at AudioUniversityOnline.com.


Speaker 0: In this video, you'll learn about comb filtering. I'll explain how it works, and I'll give you practical examples so that you can see and hear it for yourself. But if you're new here, welcome. My name is Kyle, and I've created Audio University to help you learn the fundamental concepts of audio and how to apply them. If that sounds interesting, subscribe below.

Comb filtering occurs when 2 or more identical audio signals are mixed together at a slight delay. The resulting frequency graph of these signals resembles a comb, hence the name comb filtering. To understand comb filtering, it's first important to understand the basics of phase interference. These 2 audio waves are identical and perfectly in sync or in phase. They add together to create a bigger wave.

These 2 audio signals are also identical, but they're perfectly out of sync or out of phase. They cancel when mixed together. In addition to waves being perfectly in phase and perfectly out of phase, waves can be slightly out of phase to varying degrees. Here's what a wave like this would look like on a frequency graph. Most sounds, however, are made up of many frequencies.

Here's a frequency graph of white noise which contains all frequencies. Let's pretend that these tracks are the various frequencies and white noise. I'll copy these frequencies and paste them below. Now there are 2 copies of each frequency. When the audio clips are in sync, all of the frequencies are in phase.

However, when I shift all of them by just 1 millisecond, look what happens. Some frequencies are still in phase, Some frequencies are slightly out of phase, and some frequencies are completely out of phase. Some frequencies will add together, some will cancel out, and that forms a comb on a frequency graph. A comb filter. My voice is also made up of thousands of frequencies.

Here's what my voice looks like on a frequency graph. Listen to the effect that even a slight delay can have on the sound of my voice. 0 milliseconds of delay. 10 milliseconds of delay. 20 milliseconds of delay.

There are 3 main causes of comb filtering in the real world. Reflections, multiple speakers, and multiple microphones. Let's start with comb filtering caused by reflections. The sound from this speaker takes 2 paths to the microphone. A direct path from speaker to microphone and a reflected path from speaker to wall to microphone.

The reflected sound travels a longer distance and will reach the microphone slightly later than the direct sound. Listen to the way the comb filter changes based on how far away the wall is from the speaker. Another cause of comb filtering is multiple speakers. The sound from the left speaker reaches the microphone before the sound from the right speaker. Imagine this microphone as your ear.

The sound changes depending on which speaker is closest to you. And finally, comb filtering can occur when you're using multiple microphones. Listen to the way the sound changes as the distance changes when I mix the sound from each microphone together. In future videos, we'll take a look at how to avoid phase cancellation and comb filtering, but we'll also take a look at how phase cancellation can be harnessed in technology. If you got value out of this video, click the like button, subscribe to Audio University, and check out the website at AudioUniversityOnline.com.

Thank you for watching.

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COMB FILTERING EXPLAINED: What Does a Comb Filter Sound Like?