TIPS AND TRICKS
PHASE ISSUES - WHAT IS IT AND HOW TO SOLVE IT?
In many cases it can be interesting to test several microphones on one and the same sound source. Whether it is by recording acoustic guitar in stereo with two microphones (as described in the previous article), by recording electric bass with a microphone and a live signal with a DI box, or by recording a drum kit as often involves far more than 2 microphones. Or you may include 808, synth bass or other similar effects to create more punch or fullness in the soundscape.
The moment you involve several recordings of one and the same sound source, you can encounter so-called phase issues. Phase issues are often difficult to describe, but easier to observe. This can be done by zooming in on the audio file in some recording software (often called a DAW - Digital Audio Workstation). The naked eye has difficulty observing this, but as you can see below, you can spot the problem by zooming in. Below you see a recording of an acoustic guitar with two microphones to create a stereo effect. The images below gradually zoom in on the sound waves, where with the first two images it is difficult to see what is really going on. But in the third picture you can see that the sound waves in the upper sound file move down, where the sound waves in the lower sound file move up, and vice versa.
The third image clearly shows in the selected area that the audio signal on the upper audio file first goes down, while on the lower audio file it goes up.
But what does this mean you are probably wondering now? Phase issues most often occur in the deepest or lowest tones, and have the simple explanation that bass tones come from large sound waves, which are easier to go over each other than light treble tones created by small and dense sound waves. What happens with phase errors, and specifically in the example above, is that these two audio files, together can cancel parts of the sound, and thus make it weaker, less full-bodied in the sound and it can confuse the stereo impression of the sound you have just recorded. Therefore, you may always want to check the sound wave itself as shown above in those situations where you have multiple microphones on one and the same sound source.
The solution to this can be done in several ways, of which three solutions are described here:
1. The most commonly used method is to use a so-called "polarity switch" which looks like this:
Most EQs that originally come with various DAWs have such a "polarity switch". What it does is turn the polarity of the audio signal 180 degrees. Which in turn means that if you use a "polarity switch" on the top file then the sound wave will no longer go down first within the marked area, but up (and vice versa - the other part within the marked area that goes up will in theory go down). This change can not be observed in the audio file, as it is the plugin itself that makes this digital. If you are unsure whether you have a phase error in any of your recordings, then you may want to test with such a "polarity switch". It is also not as easy to see with the naked eye if there is actually a phase issues in the audio signal, where you just have to try to make a mistake. And of course you should always choose what sounds best, not what should theoretically be right.
2. Audio files can be shifted so that the parts of the audio signal pointing down will point downwards at the same point as the other audio file. From the example above, you can move the lower audio file a little to the right so that the point where the sound wave goes up happens at the same time as it goes up on the upper sound file. Below is a picture of the same guitar tracks above where the lower audio file is offset so that the sound waves do not cancel each other out:
3. There are also some plugins that do this for you. Either Plug-ins where you manually set the time for the audio file to be shifted or where a Plug-in does this automatically for you. An example of this could be "Soundradix"'s plugin called "AutoAlign". This plugin makes automatic calculations of how large phase shifts will be required for the audio files to cancel each other as little as possible. This can be a time-efficient approach, but it is not a cheap investment. But if you use many different samples of drums or bass, it can make your everyday life even easier and the music sounds fat even faster with the help of, for example, this plug-in. There are probably many other variations of this as well. There are several mixers around the world who swear that you should use a plugin to move the audio file (and thus do not do as suggested 2. above) with various explanations, but most reasons are about leaving the audio file itself untouched.
For those who are more versed in the world of sound waves, one can of course discuss whether the phase concept is used completely correctly in this article. But that is not necessarily the purpose of this article. The purpose is for you to be able to make your music sound as good as possible. And if you get into situations where you do not make the sound sound as full and good as you want, and you use several microphones on the same source, then it may be the sound waves that cancel each other out and give you a thin and flimsy sound. And then hopefully, after reading this article, you will be able to take a closer look at whether phase errors are your problem.
Don't be afraid to try and fail with music. It's the only way to gain experience and get better at your job.