O3A Spatial Equalizer

O3A Spatial Equalizer

Host Support

Host TypeSupport





This plugin modifies a 3D O3A mix by changing sound in different directions. A canvas is shown at the bottom in the middle which can be "painted" on to control the directions that will be changed. The canvas is set out in the same way as in the O3A Visualiser and O3A Spatial Mask plugins.

This plugin combines features of the O3A Spatial Mask and O3A Graphic Equalizer plugins. It allows you to make precise changes to the frequency content of an O3A mix in particular directions, for instance to enhance a particular singer without modifying the whole mix.

The graphic equalizer is of the 31-band third-of-octave type. Parts of this plugin are implemented in the frequency domain and it has a significant latency, which hopefully your DAW will compensate for. The equalizer is linear-phase.

Sounds in different directions are separated out into two spatial channels, the "Thru" channel and the "Wet" channel. By default, the "Thru" channel is passed through unmodified and the "Wet" channel is modified by the graphic equalizer.

An ink control determines how the canvas is changed when it is clicked/drawn on. Dark ink means that sound in a particular direction should be sent to the "Thru" channel and light ink means to the "Wet". Ink in between indicates that an intermediate amount is sent to each of the two different channels. The Thru channel is modified by the Thru gain and delayed to have the same latency as the Wet channel. The Wet channel is modified by the Wet gain and also the graphic equalizer provided. The two channels are then combined.

This means that sound directions painted dark are affected by the Thru gain only and sound directions painted light are affected by the Wet gain and the equalizer. Colours in between are a mix.

That was all a bit confusing...

Yes. You might want to play with the O3A Spatial Mask and O3A Graphic Equalizer plugins to help get your head around what is going on here, before taking this plugin on. It's worth it though; this plugin makes a lot of good things possible.

The Thru and Wet gain sliders are useful, but can make things more confusing. If you set them both to "0.0" (the default) then dark means the sounds pass through unaffected and light means the equalizer is applied fully.


Most of this plugin can be automated. Pressing the buttons or drawing on the canvas are converted into changes in the internal ACN elements, so you can record these changes and play them back to reproduce canvas paint changes.

To put this another way, the ink control, brush and thru/wet/flip buttons are not accessible via automation, but the changes they make to the canvas are.

The plugin is available in the O3A Manipulators plugin library.


Controls: 20Hz - 20kHz Band Gains

These controls affect the frequency content of the soundfield at the frequency selected, in the sound directions affected by the "Thru" channel (light ink on the canvas).

If the DFT size is low, some of the frequency bands are ganged together.

Control: Ink Control

The first horizontal slider selects the colour of the "ink" that will be used when the panel is painted on. The grey tick marks are 6dB points.

Control: Thru Button

This instantly paints the entire canvas dark ("Thru"). This means that all sound directions are then affected by the Thru gain slider (and not the Wet gain or graphic equalizer).

Control: Wet Button

This instantly paints the entire canvas light ("Wet"). This means that all sound directions are then affected by the Wet gain slider and the graphic equalizer (and not the Thru gain slider).

Control: Flip Button

This instantly converts the parts of the canvas that were light to dark and the parts that were dark to light and so on. This has the effect of converting all sound direction contributions that were Thru to Wet and vice versa.

Control: Wet Gain

This sets the gain applied to sound directions that are painted as "Wet" (light).

By default this is set to "0.0" (unit gain). This means that light ink on the canvas indicates that sounds should not be changed in level. On the other hand, they will be affected by the graphic equalizer which is the main feature of this plugin.

Control: Thru Gain

This sets the gain applied to sound directions that are painted as "Thru" (dark).

By default this is set to "0.0" (unit gain). This means that dark ink on the canvas indicates that sounds should be let through the plugin unmodified.

Control: DFT Size

The DFT size is used in the internal processing of this plugin. The size can be 512, 1024, 2048, 4096, 8192, 16384, 32768 or 65536. Lower sizes give lower latency and use less CPU power, but provide a less sharp equalizer. In this case, the plugin may gang low frequency bands together.

Controls: ACN00 - ACN15 Elements

These controls are not shown on screen as numbers but are available for automation. They capture an internal representation of what is on the canvas and they can be used to automate the canvas. If you are recording them, make sure you record them all together!

We recommend that you do not attempt to interpret these numbers. However, it may be worth knowing that fading them together (linearly) will result in a natural (linear) fade of the canvas image.

Technically, these elements contain a spherical harmonic decomposition of the gain function, defined as a function mapping the surface of the unit sphere to values broadly between 0 and 1, where the spherical harmonics are encoded using the SN3D convention.