Filters are simply XML files with the extension ".eff"

Place them in a folder called `System` within your recordings folder.

The format is:

    <effect name="Filter Name">
        <filter....>
            [optional sub-components or filters]
        </filter>
        [<filter...>]
    </effect>

Currently implemented filters:

    <amplifier gain="1.0" />

Amplify (or attenuate) the sample by the given factor (1 = unity gain, 0 = silence, 2 = double, etc)

    <lfo frequency="10" depth="0.2" />

Modulate the audio with a low-frequency oscillator.  Specify the frequency and a factor of how much to modulate the audio signal.  You can also specify an optional `phase="..."` (specified in radians) as an initial phase offset for the modulation.

    <biquad type="..." fc="..." q="..." gain="..." />

A Biquad filter of the given type with a center frequency `fc` in Hz, a Q `q` and gain in Decibals of `gain`. 
Valid types are:

* lowpass
* highpass
* bandpass
* notch
* peak
* lowshelf
* highshelf

    <delay>
        <delayline samples="..." gain="...">
            [optional effects to apply to the delay line]
        </delayline>
    </delay>

A multi-tap delay line where each tap can have its own additional filters applied.  The delay is given in samples and the gain as
a factor where 1.0 is unity gain.

    <group name="Name">
        effects in the group
    </group>

Allows you to group effects together within a chain. Not of any real use yet (except that the outer wrapper of an effect chain is
actually an effect group) but may be used in the future.


An example: the "Ethereal Voice" - echoes starting off quiet and getting louder with a variable high-pass filter on the pre-echoes.  Also
includes a notch filter at 140Hz to cut out a specific annoying hum generated by my computer fans.

    <effect name="Ethereal Voice">
        <biquad type="notch" fc="140" q="20" gain="-50" />
        <amplifier gain="0.1" />
        <delayline>
            <delay samples="4000" gain="1.0">
                <biquad type="highpass" fc="400" q="1" gain="0" />
            </delay>
            <delay samples="8000" gain="1.5">
                <biquad type="highpass" fc="300" q="1" gain="0" />
            </delay>
            <delay samples="12000" gain="2.0">
                <biquad type="highpass" fc="200" q="1" gain="0" />
            </delay>
            <delay samples="16000" gain="3.0">
                <biquad type="highpass" fc="100" q="1" gain="0" />
            </delay>
            <delay samples="20000" gain="15.0" />
        </delayline>
        <biquad type="lowshelf" fc="1000" q="2.2" gain="-10" />
        <amplifier gain="1.5" />
    </effect>
