What is Audio Phasing?
When you’re working with music, tracks and sound waves, you may notice that the timing between two tracks differs when you layer one over the top of the other.
The sound waves themselves might be nearly identical, but once they’re played together, audio phasing occurs.
Audio phasing can be a difficult concept to understand but it’s important to nail some of the basics before beginning to work with music and tracks as a DJ.
Understanding Audio Phasing
Breaking Down Sound Waves
Sound waves, scientifically speaking, are vibrations in the air and changes in air pressure that produce the sounds we then hear. These waves are made of sound ripples through the air- similar to water wave ripples. It is this rippling that vibrates our eardrums and allows our brains to then interpret the vibrations as sound.
When we record audio, the instrument or microphone we are using creates sound waves through vibration and sends those sound waves outwards.
In the world of music, sound waves are generally considered to be composed of three separate things:
- Amplitude
- Wavelength
- Frequency
Amplitude
The amplitude means the volume of the wave at any particular point in time along it. If the sound wave is repeating perfectly symmetrical, any two sequential points along the wave at the same amplitude will be equal distance from one another.
Wavelength
The term wavelength refers to this distance between any two points of equal amplitude. Note that this is the length between one point at X level and the next point at the same level.
Frequency
Frequency, also sometimes referred to as the pitch, is the number of times that a sound wave repeats its entire pattern within a single second.
The Effect of Combined Sound Waves
If you have two completely identical sound waves that are aligned symmetrically, when you layer one over the top of the other, the waves (being in-phase) will increase the amplitude by exactly double. This is called constructive interference.
If the reverse were to occur, namely layer one sound wave over the top of an inverse soundwave, then the peaks of the one track and the troughs of the other track will cause destructive interference. This phase cancellation means the high and low amplitudes will in effect ‘destroy’ each other.
Phase
Now we can look at an audio phase.
In a way, the term “audio phase” refers to a specific point in time in the sound wave.
In other words, a phase of any particular sound wave refers to a particular point somewhere along the sound wave cycle. The phase in question will occur the same number of times per second as the number of times the sound wave repeats itself.
When you’re mixing audio, the two tracks being combined into one has many different elements and components that are all being mashed together. The frequency, amplitude and wavelengths can vary from track to track which means that the audio phases may sync for a time, but will most probably ‘un-sync’ themselves over time.
When two audio signals become out-of-phase with each other, you’re going to run into disjointed and out-of-time audio tracks. Hence, the importance of audio phasing.
Audio Phasing Occurrences
Whether you’re recording multiple instruments or using multiple microphones at the same time, audio phasing is something you need to be aware of. Even when you’re recording relatively simple audio–think multiple drum tracks–across separate input devices, audio phase is more likely than not to be a detracting factor.
The reason for this is that each instrument or microphone is likely placed in different places with different effects from the frequencies, reverberations and sound waves causing minute differences that are amplified when layered over the top of each other.
The result? Parts of your audio mix will sound like they are “in time” while other parts will seem to be “out of time”.
Detecting Audio Phasing
The more you work with audio, the better your ability to pick up and notice audio phasing will be. One trick to help you while you’re still learning is to listen over to your track in mono. Once condensed, have a listen to the track. Is it duller and/or thinner in sound quality? The reason may be phase cancellation. If the audio signal remains only on the right and left channels when mixing in mono, you may be experiencing audio that is out of phase.
Preventing and Fixing Phasing Issues
1. Mono Mixing
Despite the fact that most tracks will be listened to or played in stereo, mixing tracks in mono can help you keep track and identify any phasing as early as possible. The easier and quicker you can detect phasing happening, the simpler it will be for you to fix the mix. At times, you may even be able to move the one track slightly to the left or to the right to fix the issue. (See below for more.)
2. Plug-ins
Nowadays, there are numerous plug-ins you can download to help you prevent or fix the problems of audio phasing. A simple search for compatible plug-ins for the software and programs you use will yield plenty of options.
3. Placement
When you’re working with two separate microphones, a 3:1 ratio rule can be used to mitigate the effects of audio phasing. In a nutshell, simply place the second microphone three times the distance from the first microphone of the distance between the first microphone and the source of the audio you are recording.
In other words, if your instrument is at point X, and your first microphone is 5 centimetres away, then your second microphone should be 15 centimetres away from the first mic. Please note that this ratio for placement doesn’t always work but it can help to minimise the phasing with all other factors being equal.
4. Manipulating Waveforms
One manual way of fixing phasing issues with your audio is to simply move the waveforms left or right to ensure that they are aligned as they should be. This isn’t always possible or practical. Of course, there are plug-ins nowadays that do all of this for you and will automatically fix any phasing issues you may have.
5. Check your Speakers
Phase cancellation can be caused by speakers that are not wired properly. More common in household stereo equipment, the actual issue of wiring that is out-of-phase is channel polarity. To check your speakers, simply use the mono technique as this will help you detect phasing.
The Upside of Audio Phasing
Audio phasing, when unintended and unwanted, can be a real pain for the up and coming DJ. But the truth is that it does actually have its constructive uses.
Audio phasing can be used as yet another technique in your track mixing. With the requisite skill and experience, you can use the existence of phasing to your advantage and achieve the tone and sound that you’re looking for. Boosting certain frequencies and employing certain filters can help you achieve a unique and highly effective sound.
Often, the intentional use of phasing is referred to as phase music, though this term can incorporate a range of other mixing techniques.
Take your DJing to the next level with DJ City
Here at DJ City, our team is more than just experts on all things DJ Equipment. We’re bona fide enthusiasts of all things audio and music. So if you have any further questions or are still confused about sound waves, audio mixing and audio phasing, feel free to contact us today.
