Lookup Table (LUT) - Harman AudioworX

The Lookup Table (LUT) audio object performs a table lookup to create a relationship between a control input and a control output.

For example, The LUT converts vehicle speed value to gain by manipulating the speed values using a look up table. LUT module gives out values of multiple 1-D functions (i.e. control outputs) at specific query points using ‘linear’ or ‘nearest index’ or ‘lower index’ LookUp Method.

The number of columns in the LUT is configurable by modifying the number of control outputs from the SFD. The first column of the table contains one independent vector which corresponds to the x axis of the interpolation. Each of the corresponding columns corresponds to the interpolation slopes for the outputs. The number of rows of LUT denote the number of steps in interpolation of each control output.

The LUT performs LookUp Method (floor, round, linear interpolation) between values.

If the control input is below the minimum value in the x- axis, the LUT will output the minimum value in the table.
If the control output is above the maximum value, the output is limited to the maximum value in the table.

The LUT supports Axis Linearity and when enabled, LUT optimizes interpolation and assumes equally spaced steps of interpolation i.e., x-axis interpolation.

If ‘Linear Interpolation’ (LookUp Method = 1) is selected and the control input has value between two rows, then it is manipulated to create the control output vector.
If ‘Lower Index’ (LookUp Method = 2) is selected and the control input has value between two rows, then control output is the previous known control output which is the (nearest) lower index. This follows for the other control inputs.
If ‘Nearest Index’ (LookUp Method = 3) is selected and the control input has value between two rows, then control output is the nearest index (rounded value index). This follows for the other control inputs.

LUT Axis linearity is to be used with linearly spaced axis values.

Every time the LUT receives an input on its control pin, it will output on each control pin output (one per element).

Currently, the LUT is a series of dimensional tables of resolutions from 1-200. The number of elements corresponds to the number of columns. The table resolution on columns is configurable by modifying the first additional variable ‘Table Height’. Both the dependent and independent table values are configurable in the GTT. The x-axis (control-input) needs to be in ascending order and is configurable through the tuning tool.

Lookup Table Properties

Below table describes about the Lookup Table (LUT) audio object properties and functionality.

Properties	Description
Number of elements	Enter the number of channels. Range: 1 to 254 Default is set to 1.
Display Name	Display name of the LUT audio object in signal flow design. It can be changed based on the intended usage of the object.
Object Mode	LUT works in two modes. LUT 2d LUT Index

Mode

LUT audio object is used to manipulate some control input to pass to one or multiple connected objects. The object operates in two modes.

Mode

Description

LUT 2d

In the 2D mode, there is one control input, and the number of outputs varies based on the number of elements selected.

The objective of this LUT mode is to take in a control input, such as vehicle speed, and interpolate an output value, such as gain, based on values set during tuning. The output is then sent as input to other audio blocks.

Primary Success Scenario

The user will tune the object and initialize from GTT.
Capture input parameter.
Perform interpolation to determine output, based on the selected interpolation type.
Output to next object in signal flow.

LUT Index

In the Index mode, there is a second control input. This control input selects which ‘set’ of tables to use. Otherwise the modes behave the same. The number of sets is configured by the additional variable ‘LUT Depth’. The maximum depth is 8.

The objective of this mode of LUT operation is to determine output given an indexed set of tables.

Primary Success Scenario
The user will tune the object and initialize from GTT
Capture input parameters
Determine which indexed table to use
Perform interpolation to determine output, based on the selected interpolation type
Output to next object in signal flow

Additional Parameters

Following are additional parameters you can configure, for more details refer to Additional Parameters.

Table Height
UNUSED_VAR
LUT Axis Linearity
LUT Depth
LookUp Method
Block Control
Group

Parameter	Description
Table Height	This parameter corresponds to the size of each table in linear steps which can be configured through an additional configuration variable. Default height of each table in linear steps is 2. Min height of each table in linear steps is 1. Max height of each table in linear steps is 200.
UNUSED_VAR	This parameter is used to configure old variable through an additional configuration variable which is used to control how values were ramped outside of table ranges.
LUT Axis Linearity	This parameter is used to set the manipulation logic for interpolation through an additional configuration variable. Manipulation logic 0: Input axis may be unevenly spaced. This allows the user to specify table resolution where needed but requires greater effort by the object resulting in slower execution time. 1: Object assumes evenly spaced values on the input axis in order to speed operations. Default value of LUT Axis Linearity is 0.
LUT Depth	This parameter is used to determine the depth of the table which can be configured through an additional configuration variable. Default depth of each table in linear steps is 1. Min depth of each table in linear steps is 1. Max depth of each table in linear steps is 8.
LookUp Method	This parameter supports one additional configuration of LookUp Method (linear interpolation/floored index/rounded index) for values on the output axis. This decides how output is computed for an input value that is between two given input axis values. LookUp Method = 1 (Linear interpolation): This is the default type. It provides standard linear interpolation of output between two axis points. LookUp Method = 2 (Lower Index): This is Zero-hold or “previous” type of interpolation. it gives the nearest lower index which is the floor value index. For a given input, control output is the value of the output that corresponds to most previous input. LookUp Method = 3 (Nearest Index): this gives the nearest index which is the rounded value index.
Block Control	This parameter supports additional configuration of Block Control which can be enabled or disabled by selecting between Block Control Disabled (default) and Block Control Enabled. If it is enabled, all the control output signals are grouped into one control pin.
Group	The Group feature allows organizing the LUT audio objects into different groups. When the native panel of any LUT audio object is opened, all the LUT audio objects with the same group name are displayed in that native panel. If no LUT objects are assigned to any group, native panel displays all the LUT audio objects.

Tuning Parameters

The total number of tuning parameters depends on the LUT table height, table depth, and number of elements; which specifies the number of dependent output values and is equal to the number of columns in the LUT parameter table.
Hence, the number of elements = number of control outputs = number of LUT table columns.

In the LUT table, there is also an additional column for ‘LUT Index’ mode, which stores the values of x-axis interpolation points. As a result, the total number of elements in the LUT’s parameter memory is as follows.

Parameter	Description	Data Type	Range	Unit
m_Params for ‘LUT 2D’ mode	Total tuning parameters = (NUM_ELEMENTS+1) * TableHeight	Float	-99999.0 to 99999.0	None
m_Params for ‘LUT Index’ mode	Total tuning parameters = (NUM_ELEMENTS+1) * TableHeight * TableDepth	Float	-99999.0 to 99999.0	None

Control Interface

There are one or two control input values for LUT based on the mode selected.

LUT 2D: 1 float word
LUT Index: 2 float words

The first corresponds to the value that needs to be converted to control output. The second determines which table index to use for interpolation.

Name	Description	Data Type	Range	Unit
m_states [0]	Corresponds to the control input value that needs to be modified.	Float	-32768.0 to 32767.0	None
m_states [1]	Determines which table index to use for interpolation.	Float	1.0 to 8.0	None

Create LUT Object

Load xAF DLL in GTT that supports LUT.
Open the Signal Flow Designer.
Drag and drop LUT audio object into the Signal flow design view.
Verify the object is created with no error messages.

The properties and compare to these defaults.

The additional variables below are not actually object variables, they only belong to the GUI object are not covered by this document. See Global Tuning Tool User Guide for further information.

AudioObject Properties		Additional Variables
number of elements	1	Table Height	2
Object Mode	LUT 2D	UNUSED_VAR	0
		LUT Axis Linearity	0
		LUT Depth	1
		LookUp Method	1
		Block Control	0

Create LUT Object in Mode 0 (LUT 2D)

The object should already be in mode 0 (LUT 2D).
Verify there is one control input and one control output. Change the number of elements to three.
Verify the object now has three control outputs.

Create LUT Object in Mode 1 (LUT Index)

Change the object mode to LUT Index.
Verify the object now has two control inputs.
Change the number of elements to six.
Verify the object now has six control outputs.