#type: node
#context: chop
#internal: acoustic
#icon: CHOP/acoustic

= Acoustic =

"""Design audio filters and sound materials for the spatial audio
system."""

The Acoustic CHOP allows you to design audio filters and sound materials
for the SpatialAudio 3D audio system.

Three different types of filters are available:

Transmission:
    Describes which frequencies are transmitted (values close to 1) and
    which are absorbed by the material (values close to 0).
Reflection:
    Describes which frequencies are reflected off the material.
    Currently reflections are not supported.
Absorption:
    Describes which frequencies are absorbed by the filter (inverse of
    the transmission filter).
A sound material for a geometry object or a transmission filter requires
either a transmission or absorption filter. A microphone filter requires
an absorption filter.

For more information on spatial audio, see the [Spatial Audio|Node:chop/spatial] CHOP,
[Microphone|Node:obj/microphone] object, [Geometry|Node:obj/geo] object and the [Sound|Node:obj/sound] object.

When designing the filter, the CHOP graph should be in Frames mode, so
that 1 frame on the graph equals 1KHz and frame 0 corresponds to 0Hz
(DC). This means that frame 5.5 corresponds to 5.5kHz (5500Hz).

Filters cannot have negative values. If a filter has values of more than
one, it will add power to that frequency (turn on __No Resonance__ to
avoid this). A value of 0.4 in a filter will reduce that frequency by
60%.


@parameters

    == Acoustic ==

        Transmit Sound:
            If checked, a transmission filter is created.
        Reflect Sound:
            If checked, a reflection filter is created.
        Absorb Sound:
            If checked, an absorption filter is created.
        Frequency Range:
            #channels: /freqrange1-2

            The frequency range of the filter(s).
        Power:
            Selects a power conservation method. Applicable when more
            than 1 filter is being designed.

            No Power Conservation:
                Power can be reduced or amplified.
            Conserve Total Power:
                Total power is conserved but the individual frequencies'
                power is not.
            Conserve Power Per Frequency:
                Each frequency has its power conserved.
        Lock:
            If power conservation is on, moving a handle on a filter
            will adjust the other filters. This parameter allows you to
            lock one of the filters.
        No Resonance:
            Disallows filter values greater than 1.

    == Handles ==

        Handles:
            #channels: /numhandles

            The number of manipulation handles to create.
        Logarithmic Handles:
            If on, the handles are logarithmically spaced, which is more
            useful than linear spacing (off) for designing audio
            filters.
        Samples:
            #channels: /samples

            The number of samples in each filter.
        Interpolation:
            How the samples are interpolated from the handles; either
            nearest neighbor, linearly or cubically.
        Reset All Waveforms:
            Resets all filters to a constant value.

@related
    - [Node:chop/spatial]