# FreeFieldDirectivityTF

## Description

The `FreeFieldDirectivityTF`

object stores SOFA data following the
FreeFieldDirectivityTF convention. This convention stores directivities of acoustic sources
(for example, instruments, loudspeakers, singers, and talkers) in the frequency domain for
single or multiple measurements (for example, musical notes or playing styles). It considers
musical notes as a parameter directly addressing musical instruments and singers. The
measurements are performed in the free field with a single source that is surrounded by
receivers. The measured data is represented as complex frequency-domain transfer functions
(TF).

Use `sofaread`

and
`sofawrite`

to read
and write SOFA files with this convention.

## Creation

Create a `FreeFieldDirectivityTF`

object using `sofaconvention`

.

s = sofaconvention("FreeFieldDirectivityTF");

## Properties

## Data

`FrequencyResponse`

— Frequency response

`0`

(default) | *M*-by-*R*-by-*N* array

Measurements in frequency response form, specified as a complex
*M*-by-*R*-by-*N* array, where
*M* is the number of measurements, *R* is the number
of receivers, and *N* is the frequency response length.

`FrequencyVector`

— Frequency vector

1 (default) | vector

Frequency vector, in hertz, corresponding to the frequency response, specified as a vector.

`DataType`

— Type of data

`"TF"`

This property is read-only.

Type of data in the file, returned as a string.

## Listener

`ListenerPosition`

— Listener position

`[0 0 0]`

(default) | 1-by-3 matrix | *M*-by-3 matrix

Listener position in Cartesian, spherical, or spherical harmonics coordinates,
specified as a 1-by-3 or *M*-by-3 matrix, where *M* is
the number of measurements.

For more information, see Spatial Data Representations.

`ListenerPositionType`

— Listener position type

`"cartesian"`

(default) | `"spherical"`

| `"spherical harmonics"`

Listener position type, specified as `"cartesian"`

,
`"spherical"`

, or `"spherical harmonics"`

.

`ListenerPositionUnits`

— Listener position units

`"meter"`

| `"degree, degree, meter"`

This property is read-only.

Listener position units, returned as `"meter"`

if
`ListenerPositionType`

is `"cartesian"`

or
`"spherical harmonics"`

. If `ListenerPositionType`

is `"spherical"`

, the units are returned as ```
"degree, degree,
meter"
```

.

`ListenerView`

— Listener view direction

`[1 0 0]`

(default) | 1-by-3 matrix | *M*-by-3 matrix

Listener view direction, specified as a 1-by-3 or *M*-by-3 matrix,
where *M* is the number of measurements. This property defines the
direction of the positive x-axis of the local listener coordinate system.

`ListenerViewType`

— Listener view type

`"cartesian"`

(default) | `"spherical"`

Listener view type, specified as `"cartesian"`

or
`"spherical"`

.

`ListenerViewUnits`

— Listener view units

`"meter"`

| `"degree, degree, meter"`

This property is read-only.

Listener view units, returned as `"meter"`

if
`ListenerViewType`

is `"cartesian"`

or
`"degree, degree, meter"`

if `ListenerViewType`

is
`"spherical"`

.

`ListenerUp`

— Listener up direction

`[0 0 1]`

(default) | 1-by-3 matrix | *M*-by-3 matrix

Listener up direction, specified as a 1-by-3 or *M*-by-3 matrix,
where *M* is the number of measurements. This property defines the
direction of the positive z-axis of the local listener coordinate system.

## Receiver

`ReceiverPosition`

— Receiver positions

`[0 0 0]`

(default) | 1-by-3 matrix | *R*-by-3 matrix | *R*-by-3-by-*M* array

Receiver positions in Cartesian coordinates, spherical coordinates, or spherical
harmonics, specified as a 1-by-3 matrix, *R*-by-3 matrix, or
*R*-by-3-by-*M* array, where *M* is
the number of measurements. If `ReceiverPositionType`

is
`"cartesian"`

or `"spherical"`

, *R*
is the number of receivers. If `ReceiverPositionType`

is
`"spherical harmonics"`

, *R* is the number of
spherical-harmonic coefficients.

For more information, see Spatial Data Representations.

`ReceiverPositionType`

— Receiver position type

`"spherical"`

(default) | `"cartesian"`

| `"spherical harmonics"`

Receiver position type, specified as `"cartesian"`

,
`"spherical"`

, or `"spherical harmonics"`

.

`ReceiverPositionUnits`

— Receiver position units

`"meter"`

| `"degree, degree, meter"`

This property is read-only.

Receiver position units, returned as `"meter"`

if
`ReceiverPositionType`

is `"cartesian"`

or
`"spherical harmonics"`

. If `ReceiverPositionType`

is `"spherical"`

, the units are returned as ```
"degree, degree,
meter"
```

.

## Source

`SourcePosition`

— Source position

`[0 0 1]`

(default) | 1-by-3 matrix | *M*-by-3 matrix

Source position in Cartesian or spherical coordinates, specified as a 1-by-3 or
*M*-by-3 matrix, where *M* is the number of
measurements.

For more information, see Spatial Data Representations.

`SourcePositionReference`

— Description of spatial reference of source

`""`

(default) | string

Description of the spatial reference of the source position, specified as a string
(for example, `"The bell"`

for a trumpet or ```
"On the front
plate between the low- and mid/high-frequency unit"
```

for a loudspeaker). This
property provides a reference across different sources.

`SourcePositionType`

— Source position type

`"cartesian"`

(default) | `"spherical"`

Source position type, specified as `"cartesian"`

or
`"spherical"`

.

`SourcePositionUnits`

— Source position units

`"meter"`

| `"degree, degree, meter"`

This property is read-only.

Receiver position units, returned as `"meter"`

if
`SourcePositionType`

is `"cartesian"`

or
`"degree, degree, meter"`

if `SourcePositionType`

is `"spherical"`

.

`SourceView`

— Source view direction

`[1 0 0]`

(default) | 1-by-3 matrix | *M*-by-3 matrix

Source view direction, specified as a 1-by-3 or *M*-by-3 matrix,
where *M* is the number of measurements. This property defines the
direction of the positive x-axis of the local source coordinate system.

`SourceViewType`

— Source view type

`"cartesian"`

(default) | `"spherical"`

Source view type, specified as `"cartesian"`

or
`"spherical"`

.

`SourceViewUnits`

— Source view units

`"meter"`

| `"degree, degree, meter"`

This property is read-only.

Source view units, returned as `"meter"`

if
`SourceViewType`

is `"cartesian"`

or
`"degree, degree, meter"`

if `SourceViewType`

is
`"spherical"`

.

`SourceViewReference`

— Description of spatial reference of source view

`""`

(default) | string

Description of the spatial reference of the source view, specified as a string (for
example, `"Viewing direction of the bell"`

for a trumpet or
`"Perpendicular to the front plate"`

for a loudspeaker). This
property provides a reference across different sources.

`SourceUp`

— Source up direction

`[0 0 1]`

(default) | 1-by-3 matrix | *M*-by-3 matrix

Source up direction, specified as a 1-by-3 or *M*-by-3 matrix,
where *M* is the number of measurements. This property defines the
direction of the positive z-axis of the local source coordinate system.

`SourceUpReference`

— Description of spatial reference of source up direction

`""`

(default) | string

Description of the spatial reference of the source up direction, specified as a
string (for example, `"Along the keys, keys up"`

for a trumpet or
`"Perpendicular to the top plate"`

for a loudspeaker). This property
provides a reference across different sources.

`SourceManufacturer`

— Source manufacturer

`""`

(default) | string

Source manufacturer, specified as a string.

`SourceType`

— Description of acoustic source

`""`

(default) | string

Description of the acoustic source, specified as a string (for example,
`"Violin"`

, `"Singer"`

, or ```
"2-way
loudspeaker"
```

).

`SourceTuningFrequency`

— Source tuning frequency (hertz)

`0`

(default) | numeric scalar

Source tuning frequency, in hertz, to which the musical instrument is tuned corresponding to the note A4 (MIDI note number 64), specified as a numeric scalar.

## Emitter

`EmitterPosition`

— Emitter positions

`[0 0 0]`

(default) | 1-by-3 matrix | *E*-by-3 matrix | *E*-by-3-by-*M* array

Emitter positions in Cartesian coordinates, spherical coordinates, or spherical
harmonics, specified as a 1-by-3 matrix, *E*-by-3 matrix, or
*E*-by-3-by-*M* array, where *M* is
the number of measurements. If `EmitterPositionType`

is
`"cartesian"`

or `"spherical"`

, *E*
is the number of emitters. If `EmitterPositionType`

is
`"spherical harmonics"`

, *E* is the number of
spherical-harmonic coefficients.

For more information, see Spatial Data Representations.

`EmitterPositionType`

— Emitter position type

`"cartesian"`

(default) | `"spherical"`

Emitter position type, specified as `"cartesian"`

or
`"spherical"`

.

`EmitterPositionUnits`

— Emitter position units

`"meter"`

| `"degree, degree, meter"`

This property is read-only.

Emitter position units, returned as `"meter"`

if
`EmitterPositionType`

is `"cartesian"`

or
`"degree, degree, meter"`

if `EmitterPositionType`

is `"spherical"`

.

`EmitterDescription`

— General emitter description

`""`

(default) | string

General emitter description, specified as a string.

`EmitterDescriptions`

— Descriptions of each emitter

empty array (default) | *M*-by-1 string array | *E*-by-1 string array | *M*-by-1 cell array of character strings | *E*-by-1 cell array of character strings

Descriptions of each emitter, specified as an *M*-by-1 or
*E*-by-1 string array or *M*-by-1 or
*E*-by-1 cell array of character strings, where *M*
is the number of measurements and *E* is the number of emitters.

## Room

`RoomType`

— Room type

`"free field"`

(default) | string

Type of room used to perform the measurements, specified as a string.

## Metadata

`Musician`

— Description of musician

`""`

(default) | string

Description of musician, such as position or behavior, specified as a string (for
example, `"artificial excitation by R2D2"`

).

`SOFAConventions`

— Name of SOFA convention

`"FreeFieldDirectivityTF"`

This property is read-only.

Name of the SOFA convention, returned as a string.

`DatabaseName`

— Name of database

`""`

(default) | string

Name of the database that this data belongs to, specified as a string.

`Version`

— Version of specifications

`"2.1"`

(default) | string

This property is read-only.

Version of the SOFA AES69 specifications, returned as a string of the format
`"x.y"`

where `x`

is the version major and
`y`

is the version minor.

`APIName`

— Name of API

`"Audio Toolbox"`

(default) | string

This property is read-only.

Name of the API that created or edited the SOFA file, returned as a string.

`APIVersion`

— Version of API

`"1.0"`

(default) | string

This property is read-only.

Version of the API that created or edited the SOFA file, returned as a string of the
format `"x.y"`

or `"x.y.z"`

where `x`

is the version major and `y`

and `z`

are the version
minors.

`SOFAConventionsVersion`

— Version of convention set

`"1.1"`

(default) | string

This property is read-only.

Version of the SOFA AES69 convention set, returned as a string of the format
`"x.y"`

where `x`

is the version major and
`y`

is the version minor.

`Title`

— Title

`""`

(default) | string

Title containing a succinct description of the file contents, specified as a string.

`AuthorContact`

— Contact information of author

`""`

(default) | string

Contact information of the author (for example, an email address), specified as a string.

`Organization`

— Name of organization

`""`

(default) | string

Name of the organization of the author, specified as a string.

`License`

— Legal license

`""`

(default) | string

Legal license under which the data is provided, specified as a string.

`ApplicationName`

— Name of application

`"Audio Toolbox"`

(default) | string

Name of the application that created or edited the file, specified as a string.

`ApplicationVersion`

— Version of application

`"3.0.0"`

(default) | string

Version of the application that created or edited the file, specified as a string.

`Comment`

— Comment

`""`

(default) | string

Comment that can contain miscellaneous information about the data or methods used to produce the data, specified as a string.

`History`

— History

`""`

(default) | string

History defining the audio trail for modifications to the original data, specified as a string.

`References`

— References

`""`

(default) | string

Published or web-based references that describe the data or the methods used to produce the data, specified as a string.

`Origin`

— Origin

`""`

(default) | string

Origin, specified as a string representing the method used for creating the original data. In the case of model-generated data, the origin should name the model and its version. In the case of observed or measured data, the origin should characterize the data and, where possible, name the measurement method.

`DateCreated`

— Date created

string

This property is read-only.

Date and time of the creation of the file, returned as a string in ISO 8601 format
`"YYYY-MM-DD hh:mm:ss"`

. This property is set when a new file is
created.

`DateModified`

— Date modified

string

This property is read-only.

Date and time of the last file modification, returned as a string in ISO 8601 format
`"YYYY-MM-DD hh:mm:ss"`

. This property is updated when a file is
saved.

## Examples

### Create FreeFieldDirectivityTF SOFA File

Create a SOFA template object following the FreeFieldDirectivityTF convention.

`s = sofaconvention("FreeFieldDirectivityTF");`

Generate mock frequency response data to store in the file. Initialize the `FrequencyResponse`

property to store 512-point frequency responses for 25 measurements of a single receiver. Use `freqz`

to get the complex frequency responses from random Butterworth filters.

M = 25; R = 1; N = 512; s.FrequencyResponse = complex(zeros(M,R,N)); fs = 44100; for m = 1:M [b,a] = butter(5,rand); [h,f] = freqz(b,a,N,fs); s.FrequencyResponse(m,1,:) = h; end s.FrequencyVector = f;

Save the data to a SOFA file.

`sofawrite("mockFreqResponseData.sofa",s);`

## More About

### Spatial Data Representations

In this SOFA convention, you can represent spatial data using Cartesian or spherical coordinate systems with spatially discrete representations. Alternatively, you can represent spatial data with a continuous representation using spherical harmonics.

Each spatial representation stores the position data in numerical triplets (for example,
`[0 0 0]`

).

Cartesian coordinates contain three orthogonal linear values in the format

`[x y z]`

. The units of the values are meters.Spherical coordinates contain angular values for azimuth and elevation and a linear value for the radius in the format

`[azimuth elevation radius]`

. The azimuth angle, in degrees, must be in the range [0, 360). The elevation angle, in degrees, must be in the range [-90, 90]. The units of the linear radius are meters.The spatially continuous representation uses the spatial frequency domain represented by a finite series of spherical harmonics. The position data stores the real-valued spherical-harmonic coefficients in Ambisonic Channel Number (ACN) order. For spherical harmonics, only the third element of the triplet is relevant.

The number of spherical-harmonic coefficients

*N*defines the highest spherical-harmonic order*L*, where*N*=(*L*+1)^{2}.

## Version History

**Introduced in R2023b**

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