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Although phase is often seen as an evil thing when mixing audio, it does have its advantages when you’re aware you’re using it. The important thing is to learn to recognise what phase sounds like and the effect it has on your audio so that you know whether you want it there or not.
Signals - Stereo Vs Mono
With regards to phase, your main warning is that if something is too far out of phase it means that it’s not going to be properly audible when listened to in mono.
Some people might question why that matters in an age where the majority of home systems and headphones are now stereo? Your answer is specifically two ways that people still listen to music in mono: firstly is through mobile phones and mono laptop speakers (obviously these people are evil, but they do exist and if they’re listening to your music out loud through a phone or laptop, you want the mix to sound good!) Secondly is on mono sound systems in clubs and music venues.
When creating music in a digital audio workstation you have one channel of which all of your other channels are linked to, this is called the master channel (also known as Output 1-2 on Logic, the reason being because you can work in surround sound and still link to a master channel which is more than two channels in total).
The master channel is (generally) a stereo channel made up of two separate signals panned hard left and right. Now when you listen to this stereo in mono you have to consider that anything that’s hard panned 100% left or right will not be audible, and even when it’s partly panned it’s going to sound quieter in mono because mono will be playing everything that is 100% centred in the split signal properly then anything panned is essentially turned down in volume by the pan pots.
For this reason I make sure the key parts of my drum sounds i.e. kick and snare are 100% centred, as well as my sub bass. As a rule, anything below 500/600Hz is generally 100% centred and I am a bit less strict with my high mids/highs (above 4000Hz essentially) and let them have a bit more stereo space as they’re the ‘pretty’ parts of my tracks which will be more applicable to home listening.
Many producers and mix engineers recommend that ALL of your sounds are mono before effects as they would be when recorded in the analogue world and then use subtle effects to add stereo space afterwards. This isn’t always ideal now as so many plug-in instruments have stereo sounds, but there are ways you can make sure that your sounds always sound prominent, regardless whether they’re playing on a stereo or mono system, as I will go on to cover.
Phase is a result of two identical or similar sound waves overlapping one-another at a slightly different time interval. The audible effect is that some of the signal will sound louder and others will sound quieter, which happening quickly causes a slight ‘flutter’ in the left and right channels.
When a sound is in-phase it will have two of the exact same sound overlapping and the sound will be doubly as loud audibly.
When a sound is completely out of phase you will hear absolutely nothing as each of the signals will counter each other out.
Phase Invert / Reverse Phase
Unless you’re trying to cancel out noise or something in a sound you don’t want to hear, phase can be very annoying, so this is where phase inverting or reversing comes into play. The purpose of phase reverse or inverting is to swap the direction of one of your signals’ waves around so that it then becomes in phase with the other wave.
There are very powerful plugins out there which will put only certain parts of the wave back into phase so that when you have a signal which is slightly out of phase as opposed to completely, you can effectively make an out of phase stereo signal in-phase so that it will be audible on a mono signal, or just if you want it more prominent in the mix altogether.
Phase As An Effect
Chorus, flanger & (obviously) phase are all effects caused by phasing. They work in different speeds of which the two signals go out of phase and how far they go out of phase, creating dips and rises in audio in each signal which can give sounds a wider feeling across the stereo field.
More info on these effects in later tutorials.