Two Easy Methods for Distance Phasing

Intro

In this post, we’ll explore two simple methods of recreating distance-based phasing, and how these can be used and emphasized to recreate distance-based movement, without the need for complex reverberation or acoustic simulation.

Distance Phasing: What is it?

For the uninitiated, phasing happens when multiple different soundwaves with some similarity in frequency content, but difference in phase, affect each other, resulting in amplification (Superposition) and attenuation (Phase Cancellation) of different frequencies in the final perceived sound.

In a natural, non-virtual environment, any sound that finds itself in a non-vacuumized space will be perceived with some amount of phasing due to acoustic reflections. Every reflection creates a certain amount of phase cancellation with the direct sound.

When applying this phenomenon to moving sound sources, the resulting sound and its evolving phase cancellation creates an effect of audible movement, even if there is no given volume difference. This is what we describe as “Distance Phasing”.

Distance Phasing: How do we recreate it?

Without going into elaborate solutions such as complex distance-calculating reverberation, is there an easy way to recreate this effect?

There is indeed, and we will be looking at two of the simplest ways of recreating this effect!

Ultimately, the effects we are going to end up with are more akin to a manually-controller phaser rather than a complex distance-based phasing simulation, but for design purposes, these approaches cover this need very well.

We'll be using the following sound as an example for both of these methods:

All-Pass Filter

An EQ plugin with an All-Pass filter is a secret tool just waiting to be used. Using Reaper’s native ReaEQ as an example, setting a single filter to the All-Pass type, and enabling the “Show Phase” option, we’re able to see which frequencies are getting their phases shifted.

The initial effect is inaudible, as is expected for an All-Pass, but by lowering the Wet/Dry knob in the FX window, we can slowly introduce the unaffected sound into the mix, creating a noticeable filtering effect on the frequencies that are now cancelling each other. Setting the knob to 50% gives us the strongest result, as both phase-shifted and non-phase-shifted signals are reproduced at a 1:1 ratio volume.

Now here comes the real trick: Movement.

By automating the Frequency parameter in the All-Pass filter in ReaEQ, we can create a movement phasing effect somewhat similar to what distance phasing sounds!

Additionally, playing around with the Bandwidth parameter increases or decreases the range of phase-cancelling frequencies, allowing for different depths of this same effect.

ReaEQ All-Pass filter bandwidth at 0.25:

ReaEQ All-Pass filter bandwidth at 4.00:

While this approach gives us a quick and easy solution to our distance phasing needs, it merely replicates half of the phenomena present in phasing: Phase cancellation. While it is all well and good for the simpler use cases, it can sound dull when comparing it to something that does both phase cancellation as well as superposition.

Comb Filtering

A Comb Filter is the induction of a sound onto itself with a very, very short delay.

In turn, a Comb Filter plugin replicates the original sound and reproduces it on top of the original with a very, very short delay. The delay is usually defined as Hz, as the time difference is correlated to the wavelength of the selected frequency. For the purpose of this post, we’re using KiloHearts’ kHs Comb Filter plugin.

By applying a Comb Filter onto our original sound source (especially one with modulation on the Frequency parameter!), we get a result that is more akin to distance phasing than the previous All-Pass filter approach. This is due to the delayed signal not only phase-cancelling some frequencies, but superpositioning and emphasizing other as well.

Similar to the All-Pass filter effect, the strongest effect occurs with the Mix at 50%, since the same 1:1 volume ratio applies to the original and delayed signal.

Conclusion

With only All-Pass filtering and Comb Filtering, you can already create some fairly believable distance phasing:

However, while distance phasing is an essential part when designing sounds that either move towards or away from the listener, you should not rely solely on these effects and volume fading for this sort of work!

Additional details such as reverb, distance filtering, diffraction, echoes and delays, all of these and many more are as crucial to recreate spatial distance as distance phasing is. It’s all about mixing and matching what’s fitting, and finding your own preferences and approach to dealing with this sort of design work.

Have fun!