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Wave Field Synthesis (WFS)

Wave Field Synthesis is a technique that aims at recreating exactly the wave front a sound source would have created at its specified position. It relies on delay and level differences. As such, it has the advantage that the localization of sounds will be correctly perceived at any position in the audience area.

Learn more about Wave Field Synthesis with our Spatialization Guides.

Speaker Layout Requirements

New in HOLOPHONIX 2.0

Wave Field Synthesis is now available on 3D loudspeaker setups. You can now extend the many advantages of Wave Field Synthesis to immersive loudspeakers.

Loudspeaker orientation

WFS now takes into account your loudspeakers' orientation.

You can use the WFS algorithm on frontal loudspeaker arrays, but also on immersive setups, including elevation speakers.

For sound reinforcement applications, we recommend you follow these guidelines:

  • Crate a bus containing your Main frontal speakers, Surround speakers, and Delay speakers. Your Delay loudspeakers will be automatically time-aligned on your Main speakers.
  • Create a separate bus for your Front-Fill speakers. With the Speakers Parameters window, change the z Coordinate of the front fill speakers, and align them with the Main speakers' z Coordinate.

Alternatively, if you want to manually adjust the time alignment of your Delay loudspeakers, you can either:

  • Add an individual delay to each Delay speakers in the Speakers Parameters window;
  • Or create a separate bus for your Delay speakers. In that case, you will need to manually adjust the delay of the array using the Bus Delay.

WFS Parameters

note

Default parameters were chosen to ensure optimal results for sources with a fixed position or with slow movements. Some optimizations are available to enhance WFS in common use cases such as Front Fills optimization.

To tune the WFS algorithm, you can switch to Advanced Settings mode, and access more in-depth settings. However, for most uses we recommend working the default settings.

Front Fill Optimization

Depreciated Parameter

This option has been removed in HOLOPHONIX 2.1. This setting used to set the Gain Scaling at 80%. Switch to "Advanced Settings" to change the Gain Scaling.

For more advanced Front Fill Optimisation, see the LSO optimisation for front fills.

WFS Pre-Filter

Activate this parameter to compensate dynamically for the extra bass amplification caused by the WFS array. This will apply a low shelf filter automatically computed depending on the distance between the loudspeakers.

2D mode

Activate this parameter to switch your bus to 2D mode. In 2D mode, the height (Z) parameter of sources or speakers will have no effect on the resulting spatialization.

Delay Smoothing Time

When a source is moved from one position to another, artifacts are caused by the delay change. HOLOPHONIX applies a smoothing on delay changes. Adjust the smoothing time depending both on the speed of the movements and your audio content.

info

For more control over the delay smoothing parameters, switch to Advanced Settings.

WFS Advanced Parameters

WFS Pre-Filter

Activate this parameter to compensate dynamically for the extra bass amplification caused by the WFS array. This will apply a low shelf filter automatically computed depending on the distance between the loudspeakers.

Delay Scaling

This setting allows the user to modify proportionally the delay values, by decreasing the delay differences (under 100%) or increasing them (over 100%).

The chosen percentage will act as a multiplication factor for the set of delay values applied. When the delay scaling is set to 200%, all delays will have double the value they had at 100%, while at 50% they will have half the value. Setting the delay scaling at 0% will set all delays to 0 ms, only the level differences will remain.

The delay scaling has a direct impact on the filtering effects (coloration) that are caused by the delays when moving a source. Depending on the audio signal, this comb filtering-like sensation can be more or less disturbing.

tip

In most cases, a Delay Scaling value around 90% preserves a natural timbre, while maintaining a good spatial accuracy when changing grid position.

Delay Scaling can be used to modify the shape of the wave front, making it closer to a plane wave for values under 100%, or to increase the delays between the speakers for values over 100%, thus relying more on the precedence effect for the perception of sound localization.

Gain Scaling

This setting allows modifying the differences between the gain values by decreasing them (under 100%), or increasing them (over 100%).

tip

Use this setting when sources are positioned close to the WFS speaker array. With a setting a little bit lower than 100%, you will start using more loudspeakers, and enhance the perception for listeners closer to the array.

Interpolation Parameters

When moving a source from one position to another, the algorithm will have to shift from one set of gain and delay values to another. These parameters allow the user to choose how this interpolation will be performed.

Delay Smoothing Mode

When a source is moved from one position to another, the delay value has to change continuously. Changing a delay continuously creates artifacts, no matter what method is used. But depending on your audio signal (voice, rhythmic or melodic instrument, etc.), and the type of movements, you might prefer one method over another.

Variable Delay method will apply a variable delay, causing a Doppler-like effect (pitch variation).

Crossfade method applies a crossfade between signals, causing comb-filtering (coloration).

Inter-Sample Delay Interpolation Mode

Theoretically, in digital audio, a delay value can only be a multiple of the sample rate. To allow a smooth delay transition when a source is moved, it is necessary to apply delay values in between samples. Several methods allow to do that, each with its pros and cons. The recommended method is All Pass.

Lagrange 3 mode computes more precise delay values, but introduces delay-dependent filtering and phase delay in the audible spectrum, unless it is used at an oversampling frequency (i.e. at a sample rate ≥ 88.2 kHz or 96 kHz).

All Pass mode has the advantage to offer an excellent tone fidelity, as it does not introduce filtering. Delay values are not as precise as Lagrange 3, but are, but at the cost of less precise delay values. However, this method is more CPU-Intensive.

tip

We recommend using All Pass as it offers excellent results and does not require oversampling.

Delay Smoothing Time

The Delay Smoothing Time corresponds to the time it will take to shift from one set of delay values to another. If you need to change this parameter, take into account the audio characteristics of your source (tone, sustained or percussive, ...), as well as the speed of its movements. You can also try changing this parameter along with Interpolation Mode.

Gain Smoothing Time

The Gain Smoothing Time is the time it will take to shift from one set of gain values to another.

Minimal Delay Mode (Zero Latency)

When disabled, the bus calculates source delays and gains related to their distance from the speaker array. Thus, moving a source away from the speaker array increases the source delay.

When enabled (Minimal Delay or Zero Latency mode), the bus subtracts the delay between the source and the nearest speaker. The delay and gain differences between the loudspeakers remain identical. It results in a lower source delay, while keeping the sonic image unchanged.

WFS Windowing (Gain Reduction Optimisation)

Activate this parameter to smooth out the edges of the wavefront at the extremities of the WFS array. This will prevent undesired localization artefacts. In practice, windowing will apply gain reduction for speakers located on the opposite side of the virtual source.

Window Size

This parameter determines by percentage the windowing effect’s factor. When set to 0%, no windowing will be applied. 100% is the maximum allowed windowing. Default value is 30%.

LSO Front Fills Optimization

LSO (Large Stage Optimizer) is an optimization developed for very wide stages, when the listeners are seated close to the loudspeakers (like front-fills for example).

When you position a virtual source close to the loudspeakers, only the closest loudspeakers will be used. If listeners are close to the WFS array (which is the case with front-fills), the listeners that are on the opposite side of the source will not get any signal of the source in the loudspeakers in front of them.

To avoid that effect, you can use the LSO (Large Stage Optimisation). It will apply a wider gain distribution (i.e., there will be more sound on the loudspeakers further away from the source). Therefore, the listeners that are on the opposite side of the source will get more sound and keep a good intelligibility.

How does it work?

LSO applies a dynamic Gain Scaling depending on the source’s distance to the loudspeakers. When a virtual source is placed close to the loudspeakers, the gain scaling of that source will be increased, therefore spreading that source's signal over more loudspeakers. When the virtual source is further away from the speakers, no gain scaling will be applied.

You can use the LSA EQ to choose a target a specific frequency range for the additional spread signal.

Speaker Setup

LSO optimisation will only work on frontal systems, without surrounds.

Show LSO

Display a visualization of the LSO range of action. The red line indicates the threshold where the dynamic gain spreading will be applied to sources.

LSO Bus EQ

Adjust the equalization of the LSO bus. You can use it to target the speech intelligibility range, for example.

LSO Gain

Adjust the level of the additional spread signal of the LSO Bus.

Stage Depth

The stage depth will impact the positioning threshold where the dynamic gain spreading is applied.

LSO Curvature

This setting adjusts the curvature of the positioning threshold where the dynamic gain spreading is applied. It ranges from 30% to 300%.