Become a member
Become a member
Continuer avec Google

or
Log in
Log in
Se connecter avec Google

or
learning

Understanding Phase

Everything about Phase Problems - Part 1

If you are into audio, you have surely heard about phase many times — whether in reference to mixing or recording live in the studio — and usually in a negative way.

View other articles in this series...

Most times, beginners suffer from these phase "problems" without being aware of it. They just know something is wrong with the sound, but don't really know what it is or where the problem is coming from, and they grope for what almost always ends up being a dubious solution. Yet, you don't have to be a rocket scientist to understand phase and it might even become a precious ally if you dig a bit deeper into it. So, with that in mind, in this first part, we will address the issue in a simple manner to better understand the theory behind that nasty phase!

Genesis

To simplify our task, let us consider one of the simplest sounds there is, a sine wave, which is made out of regularly alternating "peaks" and "valleys" (in this case at a frequency of 440Hz).In the beginning there was sound. As you know, sound is basically vibrations propagating through the air in the form of pressure variations. When you capture a sound with a microphone, the former is transformed by the latter into an electrical signal that can be represented with a waveform.

Comprendre la phase

If you add to that first signal an identical sine wave, perfectly lining up the "peaks" and "valleys" (which means without any delay between them), you get a waveform oscillating at the same frequency, but with a 6dB increase in amplitude. It is said that these two signals are in phase.

Conversely, if you align the "peaks" of one with the "valleys" of the other, the signals will cancel each other out and you will get absolute silence. It is said that the signals are out of phase. 

Comprendre la phase
In phase
Comprendre la phase
Out of phase
 

 

Comprendre la phase

Without going to such extremes, any delay between two signals will result in a more or less intense level change at the output. This delay is called phase difference or phase shift and is expressed in degrees. A phase difference of 180° corresponds to an out-of-phase phenomenon, while a difference of 360° makes the waves line up perfectly again, but with a phase shift of one full cycle.


 

Comb filter

Comprendre la phase

All that theory is very nice, but in real life you will hardly ever find yourself working with a pure sine wave. However, regardless of the complexity of the waveform, it will always be the combination of simpler waveforms at different frequencies. Thus, in the example opposite, the third waveform is the sum of the two others. While it is easy to understand what happens to a signal when we superimpose an identical in-phase or out-of-phase signal (an amplitude increase of 6dB or absolute silence, respectively, for those who aren't paying attention!), what happens when you apply a small delay that results in a phase shift of just a couple of degrees between both waveforms?

Comprendre la phase

What you get is a phenomenon known as comb filtering, which is basically the reinforcement and cancellation of different frequency zones, as you can see in a spectrum analyzer. The red curve here represents the two signals in phase, while the green one shows the result of the delay in the previous image. This phenomenon can be easily explained taking apart a complex signal into simpler waveforms. It is thus easy to understand that delay leads to phase problems with certain waveforms, but not with others, and that's where the comb filter in the spectrum analyzer comes from.

To be continued…

 

After reading this article, it seems obvious that phase issues can easily ruin your work. In an upcoming article we will dig further into this matter to turn this problem into an opportunity.

Next article in this series:
Phase — Practical Cases →

Vous souhaitez réagir à cet article ?

Log in
Become a member
cookies

We are using cookies!

Yes, Audiofanzine is using cookies. Since the last thing that we want is disturbing your diet with too much fat or too much sugar, you'll be glad to learn that we made them ourselves with fresh, organic and fair ingredients, and with a perfect nutritional balance. What this means is that the data we store in them is used to enhance your use of our website as well as improve your user experience on our pages (learn more). To configure your cookie preferences, click here.

We did not wait for a law to make us respect our members and visitors' privacy. The cookies that we use are only meant to improve your experience on our website.

Our cookies

Cookies not subject to consent

These are cookies that guarantee the proper functioning of Audiofanzine and allow its optimization. The website cannot function properly without these cookies.

Website preferences

We store your preferences so that you do not have to re-enter them every time your come back (forums options, dark or light theme, classifieds filter, standard or buzz news, newsletters popups...).

Log in

This one makes sure you don't have to re-enter your credentials every time you visit Audiofanzine.

Analytics

This data allows us to understand the use that our visitors make of our website in an attempt to improve it.

Advertising

This information allows us to show you personalized advertisements thanks to which Audiofanzine is financed. By unchecking this box you will still have advertisements but they may be less interesting :)

We did not wait for a law to make us respect our members and visitors' privacy. The cookies that we use are only meant to improve your experience on our website.

Our cookies

Cookies not subject to consent

These are cookies that guarantee the proper functioning of Audiofanzine and allow its optimization. The website cannot function properly without these cookies.

Website preferences

We store your preferences so that you do not have to re-enter them every time your come back (forums options, dark or light theme, classifieds filter, standard or buzz news, newsletters popups...).

Log in

This one makes sure you don't have to re-enter your credentials every time you visit Audiofanzine.

Analytics

This data allows us to understand the use that our visitors make of our website in an attempt to improve it.

Advertising

This information allows us to show you personalized advertisements thanks to which Audiofanzine is financed. By unchecking this box you will still have advertisements but they may be less interesting :)


You can find more details on data protection in our privacy policy.