@Override
    public void write(JmeExporter ex) throws IOException {
        super.write(ex);
        OutputCapsule oc = ex.getCapsule(this);
        oc.write(volume, "volume", 1f);
        oc.write(highFreqVolume, "hf_volume", 1f);
    }
Sets the overall volume.

@param volume the new overall volume scaling (0.0 - 1.0).
@throws IllegalArgumentException if {@code volume} is out of range.
jme3-core/src/main/java/com/jme3/audio/LowPassFilter.java