Skip to main content
Version: 2.0

Wave Field Synthesis (WFS) Bus

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.

Speaker Layout Requirements

New in HOLOPHONIX 2.0

Wave Field Synthesis is now available on 3D loudspeaker setups.

WFS Parameters

Default parameters were chosen to ensure optimal results for sources with a fixed position or with slow movements.

Front Fill Optimization

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 will not get any signal of the source in the loudspeakers in front of them. To avoid that effect, simply activate the Front Fill Optimization, that will apply a wider gain distribution.

info

To explore more advanced front-fills optimization parameters, see the Advanced Front-Fills Optimization section.

Interference Compensation Pre-Filter

See this section.

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 (see this section. Adjust the smoothing time depending both on the speed of the movements and your audio content.

WFS Advanced Parameters

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.

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.