.. _gettingStartedFeedbackDoc:

.. index:: single: Example; Feedback and Processor Modules

==============================
Feedback and Processor Modules
==============================
Let's create a feedforward comb filter as shown in Figure 1. This can be achieved by using the :ref:`FixedDelay() <FixedDelay_SCP>` processor.

.. figure:: Images/FeedforwardCombFilter.png
   :scale: 75%
   :alt: Feedforward Comb Filter
   :align: center
   
   **Figure 1:** Feedforward Comb Filter.

::
	
	signal DelayedSignal {		
		default:	0.0
		rate:		AudioRate
		reset:		MasterReset
		meta:		none
	}
	
	# Feedforward Comb Filter Implementation
	AudioIn[1]
	>> FixedDelay (
		samples:	32
		default:	0.0
		reset:		off
		bypass:		off
	)
	>> DelayedSignal;
	
	[ AudioIn[1], DelayedSignal ]
	>> Level (
		gainType:	'Linear'
		gain: 		[ 0.5, 0.45 ]
		offset:		0.0
		bypass:		off
	)
	>> Mix ()
	>> AudioOut[1];

	
.. figure:: Images/FeedforwardCombFilterImplementation.png
   :scale: 85%
   :alt: Feedforward Comb Filter Implementation
   :align: center
   
   **Figure 2:** Feedforward Comb Filter Implementation.

----

Let's create a feedback comb filter as shown in Figure 3. 

.. figure:: Images/FeedbackCombFilter.png
   :scale: 75%
   :alt: Feedback Comb Filter
   :align: center
   
   **Figure 3:** Feedback Comb Filter.

::
	
	signal Feedback {
		default:	0.0
		rate:		AudioRate
		reset:		MasterReset
		meta:		none
	}
	
	# Feedback Comb Filter Implementation
	[ AudioIn[1], Feedback ]
	>> Level (
		gainType:	'Linear'
		gain: 		[ 0.5, -0.45 ]
		offset:		0.0
		bypass:		off
	)
	>> Mix ()
	>> AudioOut[1]
	>> FixedDelay (
		samples:	32
		default:	0.0
		reset:		off
		bypass:		off
	)
	>> Feedback;
	
	
.. figure:: Images/FeedbackCombFilterImplementation.png
   :scale: 85%
   :alt: Feedback Comb Filter Implementation
   :align: center
   
   **Figure 4:** Feedback Comb Filter Implementation.

----

Let's create an allpass filter as shown in Figure 5. 

.. figure:: Images/Allpass.png
   :scale: 75%
   :alt: Feedforward Comb Filter
   :align: center
   
   **Figure 5:** Allpass Filter.

::

	signal FeedForward {
		default:	0.0
		rate:		AudioRate
		reset:		MasterReset
		meta:		none
	}
	
	signal Feedback {
		default:	0.0
		rate:		AudioRate
		reset:		MasterReset
		meta:		none
	}

	# Allpass Filter Implementation 
	
	

	[ AudioIn[1], Feedback ]
	>> Level (
		gainType:	'Linear'
		gain: 		[ 1.0, -0.90 ]
		offset:		0.0
		bypass:		off
	)
	>> Mix ()
	>> Feedforward
	>> FixedDelay (
		samples:	32
		default:	0.0
		reset:		off
		bypass:		off
	)
	>> Feedback;
	
	[ Feedback, FeedForward ]
	>> Level (
		gainType:	'Linear'
		gain: 		[ 1.0, 0.90 ]
		offset:		0.0
		bypass:		off
	)
	>> Mix (
		gainType:	'Linear'	
		gain: 		0.5
		offset:		0.0
		bypass:		off
	)
	>> AudioOut[1];
	
.. figure:: Images/AllpassImplementation.png
   :scale: 66%
   :alt: Allpass Filter Implementation.
   :align: center
   
   **Figure 6:** Allpass Filter Implementation.

----

Let's create an biquad filter as shown in Figure 7. 

.. figure:: Images/BiquadFormII.png
   :scale: 75%
   :alt: Biquad Filter Direct Form II
   :align: center
   
   **Figure 7:** Biquad Filter Direct Form II. (source: Wikipedia)

::

	constant A [2] {
		value:	[0.0, 0.0]
		meta:	'Output difference polynomial coefficients.'
	}
	
	constant B [3] {
		value:	[1.0, 0.0, 0.0]
		meta:	'Input difference polynomial coefficients.'
	}

	signal Z [3] {
		default:	0.0
		rate:		AudioRate
		reset:		MasterReset
		meta:		none
	}
	
	
	[ AudioIn[1], Z[2], Z[3] ]
	>> Level (
		gainType:	'Linear'	
		gain: 		[ 1.0, -A[1], -A[2] ]
		offset:		0.0
		bypass:		off
	)
	>> Mix ()
	>> Z[1]
	>> FixedDelay (
		samples:	1
		default:	0.0
		reset:		off
		bypass:		off
	)
	>> Z[2]
	>> FixedDelay (
		samples:	1
		default:	0.0
		reset:		off
		bypass:		off
	)
	>> Z[3];
	
	[ Z[3], Z[2], Z[1] ]
	>> Level (
		gainType:	'Linear'	
		gain: 		[ B[3], B[2], B[1] ]
		offset:		0.0
		bypass:		off
	)
	>> Mix ()
	>> AudioOut[1];

----
	
The following block declares a processor block for reuse. The examples is based on the Biquad filter example. 
	
::

	module Biquad {
		input:			Input
		output:			Output
		propertyName:		[ 'inputCoefficients', 'outputCoefficients', 'reset', 'bypass' ]
		propertyDirection:	in
		propertyBlock: 		[
			constant B [3] { value: [ 1.0, 0.0, 0.0 ] }, 
			constant A [2] { value: [ 0.0, 0.0 ] },
			trigger Reset {},
			switch Bypass { default: off reset: none }
		]
		internalBlock:		[ 
			signal Input { rate: streamRate reset: Reset },
			signal Output { rate: streamRate reset: Reset },
			signal Z [3] { rate: streamRate reset: Reset },
		]
		streams:		[ 
			[ Input, Z[2], Z[3] ]
			>> Level (
				gainType:	'Linear'	
				gain: 		[ 1.0, -A[1], -A[2] ]
				offset:		0.0
				bypass:		off
			)
			>> Mix ()
			>> Z[1]
			>> FixedDelay (
				samples:	1
				default:	0.0
				reset:		Reset
				bypass:		off
			)
			>> Z[2]
			>> FixedDelay (
				samples:	1
				default:	0.0
				reset:		Reset
				bypass:		off
			)
			>> Z[3];
			,
			[ Z[3], Z[2], Z[1] ]
			>> Level (
				gainType:	'Linear'	
				gains:		[ B[3], B[2], B[1] ]
				offset:		0.0
				bypass:		off
			)
			>> Mix ()
			>> Result;
			,
			Bypass
			>> Select (
				whenOn:		Input
				whenOff:	Result
			)
			>> Output;
		]
		meta:			none
	}

	constant Y [2] {
		value:	[0.0, 0.0]
		meta:	'Output difference polynomial coefficients.'
	}
	
	constant X [3] {
		value:	[1.0, 0.0, 0.0]
		meta:	'Input difference polynomial coefficients.'
	}
	
	AudioIn[1] 
	>> Biquad (
		inputCoefficients: 	X
		outputCoefficients:	Y
		reset:			off
		bypass: 		off
	)
	>>  AudioOut[1];