Phase occurs when two signal are time shifted. In other words, one signal will be offset by a specific amount to another. Basically, the phase is the progression along the cycle of the waveform determined as degrees. A 360 degree phase is one complete cycle of a waveform where 0 degress is the start of the cycle. If two signals are aligned exactly in time and location then they are deemed to be in phase. If they are not then they are deemed to be out of phase. Short of going into an epic debate about the subject of phase it is probably best to explain what happens when signals are either in or out of phase. I will use a basic sine wave in stereo and then show you what happens when it is in phase and then 180 degrees out of phase (total phase cancellation).
Both sine waves are in phase and aligned perfectly.
By moving the other sine wave by 180 degrees (inverting), which is halfway along the cycle, we are able to see what happens when they are summed. This waveform is now 180 degrees out of phase. That means it has moved 180 degrees (upside down or inverted). In other words the peaks of the cycle coincide identically with the troughs of the other cycle. If I now sum these two channels to one mono output I should get silence (cancel out). This is called total phase cancellation.
Once the channels are summed you get the following; total phase cancellation.
Because total phase cancellation has taken place the result is simply silence.
If you vary the amount of phase by degrees you get partial phase cancellation and so on whereby some frequencies are cancelled. This teaches us what happens with phase and how varying amounts of it affect the result. In terms of using phase in effects the results can be honed to taste depending on how much and what type (positive/negative) are used.
Phasing behaves in much the same way as chorus and flanging but with shorter delay times and the effect itself is far more subtle. Because phasing works with shorter delay times than chorus and flanging the impression is that there is only one sound as opposed to two distinct sounds and because the LFO modulates frequencies (peaks and trough, also known as notches) the filtering effect is quite pleasing. Unlike flangers which use delay lines phasers use all pass networks/stages which are all pass filters and by adjusting the frequencies, and phase, of the stages different phase effects can be created. By going back to the principles of phase earlier in this tutorial we can then see how certain frequencies cancel each other out and therefore create different textures.
Phasers can be used to add swirls to sounds or to completely maul a sound into something else. Because it is a subtle effect it doesn’t mean you can’t extreme it for sound design purposes. As with all effects and dynamics it is up to the individual to explore and experiment.
One of the more ‘delicious’ studio effects. Let me run through how it works and how to use it.
Topics covered in this video are:
- What is it, how to use it and when to use it
- Phase Shift
- Low Frequency Oscillator
- Stages and Rate
- Filters and Resonance Mode
- Positive and Negative Response
- Notch and Notch Phase
- All Pass Filters