General information on SOFA - Revision history

Isfmiho: Typical HRTF/DRIR measurement setup figure added; old links remain as "source"

2020-10-30T07:00:54Z

Typical HRTF/DRIR measurement setup figure added; old links remain as "source"

← Older revision		Revision as of 09:00, 30 October 2020
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	One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] measured in human listeners was the CIPIC database [2]⁠. The measurements were performed at a constant distance of 1 m for 1250 spatial directions around the listener. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are available for 43 listeners as IRs of 200 samples at a sampling rate of 44.1 kHz. Since then many other [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIR databases have been made publicly available [3–8]⁠.		One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] measured in human listeners was the CIPIC database [2]⁠. The measurements were performed at a constant distance of 1 m for 1250 spatial directions around the listener. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are available for 43 listeners as IRs of 200 samples at a sampling rate of 44.1 kHz. Since then many other [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIR databases have been made publicly available [3–8]⁠.

			[[File:Typical HRTF measurement.png\|right\|thumb\|225px\|Fig. 1: Typical HRTF/DRIR measurement setup]]
⚫	All those measurement setups have the following properties in common. In an anechoic chamber or in a room, excitation signals are generated and microphones are used to record the incoming signals (see Fig. 1 ~~from~~ [http://sourceforge.net/projects/sofacoustics/files/SOFA%20specs%200.1%20%28as%20of%20AES%202013%29.pdf/download ~~here~~]). The measurement is repeated while varying the spatial position of the excitation source relative to the listener, which is done by varying the position of the listener, the sound source, or both in different dimensions.

⚫	Binaural [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] measurement setups use only two microphones to record the left and right ear signals. However, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIRs measurements may also consider multiple microphones, e.g., three microphones per head side in hearing-assist devices [7]⁠, tens of microphones arranged in an array structure at different directions and distances from the center [9]⁠, a multichannel microphone array arranged around the listeners in a reciprocal [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] measurement system [10], [11]⁠, multichannel microphone arrays for measuring DRIRs [12]⁠ or various microphone positions in a room, e.g., for concert-hall acoustics measurements [13]⁠. As a generalization, microphones and an object comprising those microphones can be identified. Thus, in this article, a microphone as the single receiver of the sound field is called the receiver, and the comprising all the receivers is called the listener, see Fig. 1 ~~from~~ [http://sourceforge.net/projects/sofacoustics/files/SOFA%20specs%200.1%20%28as%20of%20AES%202013%29.pdf/download ~~here~~].
		⚫	All those measurement setups have the following properties in common. In an anechoic chamber or in a room, excitation signals are generated and microphones are used to record the incoming signals (see Fig. 1, [http://sourceforge.net/projects/sofacoustics/files/SOFA%20specs%200.1%20%28as%20of%20AES%202013%29.pdf/download source]). The measurement is repeated while varying the spatial position of the excitation source relative to the listener, which is done by varying the position of the listener, the sound source, or both in different dimensions.
		⚫	Binaural [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] measurement setups use only two microphones to record the left and right ear signals. However, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIRs measurements may also consider multiple microphones, e.g., three microphones per head side in hearing-assist devices [7]⁠, tens of microphones arranged in an array structure at different directions and distances from the center [9]⁠, a multichannel microphone array arranged around the listeners in a reciprocal [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] measurement system [10], [11]⁠, multichannel microphone arrays for measuring DRIRs [12]⁠ or various microphone positions in a room, e.g., for concert-hall acoustics measurements [13]⁠. As a generalization, microphones and an object comprising those microphones can be identified. Thus, in this article, a microphone as the single receiver of the sound field is called the receiver, and the comprising all the receivers is called the listener, see Fig. 1 ([http://sourceforge.net/projects/sofacoustics/files/SOFA%20specs%200.1%20%28as%20of%20AES%202013%29.pdf/download source]).

	The sound source used for the excitation signal is not necessarily a single point source. Loudspeaker arrays were used, either to control the sound field surrounding the listener, e.g., wave-field synthesis [11], [14], [15]⁠, or higher-order Ambisonics [16], [17]⁠ or to control the radiation characteristics of the sound sources [18]⁠. Similarly to the concept of listener and receivers, in this article, the particular sources creating the excitation signal are called emitters and the object comprising the emitters is called source. Note that a measurement setup with a source with multiple emitters and a listener with multiple receivers has already been considered [19]⁠.		The sound source used for the excitation signal is not necessarily a single point source. Loudspeaker arrays were used, either to control the sound field surrounding the listener, e.g., wave-field synthesis [11], [14], [15]⁠, or higher-order Ambisonics [16], [17]⁠ or to control the radiation characteristics of the sound sources [18]⁠. Similarly to the concept of listener and receivers, in this article, the particular sources creating the excitation signal are called emitters and the object comprising the emitters is called source. Note that a measurement setup with a source with multiple emitters and a listener with multiple receivers has already been considered [19]⁠.

Petibub: /* Typical measurement setups */

2020-03-28T10:42:23Z

Typical measurement setups

← Older revision		Revision as of 12:42, 28 March 2020
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	One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] measured in human listeners was the CIPIC database [2]⁠. The measurements were performed at a constant distance of 1 m for 1250 spatial directions around the listener. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are available for 43 listeners as IRs of 200 samples at a sampling rate of 44.1 kHz. Since then many other [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIR databases have been made publicly available [3–8]⁠.		One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] measured in human listeners was the CIPIC database [2]⁠. The measurements were performed at a constant distance of 1 m for 1250 spatial directions around the listener. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are available for 43 listeners as IRs of 200 samples at a sampling rate of 44.1 kHz. Since then many other [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIR databases have been made publicly available [3–8]⁠.

	All those measurement setups have the following properties in common. In an anechoic chamber or in a room, excitation signals are generated and microphones are used to record the incoming signals (see Fig. 1). The measurement is repeated while varying the spatial position of the excitation source relative to the listener, which is done by varying the position of the listener, the sound source, or both in different dimensions.		All those measurement setups have the following properties in common. In an anechoic chamber or in a room, excitation signals are generated and microphones are used to record the incoming signals (see Fig. 1 from [http://sourceforge.net/projects/sofacoustics/files/SOFA%20specs%200.1%20%28as%20of%20AES%202013%29.pdf/download here]). The measurement is repeated while varying the spatial position of the excitation source relative to the listener, which is done by varying the position of the listener, the sound source, or both in different dimensions.
	Binaural [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] measurement setups use only two microphones to record the left and right ear signals. However, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIRs measurements may also consider multiple microphones, e.g., three microphones per head side in hearing-assist devices [7]⁠, tens of microphones arranged in an array structure at different directions and distances from the center [9]⁠, a multichannel microphone array arranged around the listeners in a reciprocal [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] measurement system [10], [11]⁠, multichannel microphone arrays for measuring DRIRs [12]⁠ or various microphone positions in a room, e.g., for concert-hall acoustics measurements [13]⁠. As a generalization, microphones and an object comprising those microphones can be identified. Thus, in this article, a microphone as the single receiver of the sound field is called the receiver, and the comprising all the receivers is called the listener, see Fig. 1.		Binaural [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] measurement setups use only two microphones to record the left and right ear signals. However, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIRs measurements may also consider multiple microphones, e.g., three microphones per head side in hearing-assist devices [7]⁠, tens of microphones arranged in an array structure at different directions and distances from the center [9]⁠, a multichannel microphone array arranged around the listeners in a reciprocal [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] measurement system [10], [11]⁠, multichannel microphone arrays for measuring DRIRs [12]⁠ or various microphone positions in a room, e.g., for concert-hall acoustics measurements [13]⁠. As a generalization, microphones and an object comprising those microphones can be identified. Thus, in this article, a microphone as the single receiver of the sound field is called the receiver, and the comprising all the receivers is called the listener, see Fig. 1 from [http://sourceforge.net/projects/sofacoustics/files/SOFA%20specs%200.1%20%28as%20of%20AES%202013%29.pdf/download here].

	The sound source used for the excitation signal is not necessarily a single point source. Loudspeaker arrays were used, either to control the sound field surrounding the listener, e.g., wave-field synthesis [11], [14], [15]⁠, or higher-order Ambisonics [16], [17]⁠ or to control the radiation characteristics of the sound sources [18]⁠. Similarly to the concept of listener and receivers, in this article, the particular sources creating the excitation signal are called emitters and the object comprising the emitters is called source. Note that a measurement setup with a source with multiple emitters and a listener with multiple receivers has already been considered [19]⁠.		The sound source used for the excitation signal is not necessarily a single point source. Loudspeaker arrays were used, either to control the sound field surrounding the listener, e.g., wave-field synthesis [11], [14], [15]⁠, or higher-order Ambisonics [16], [17]⁠ or to control the radiation characteristics of the sound sources [18]⁠. Similarly to the concept of listener and receivers, in this article, the particular sources creating the excitation signal are called emitters and the object comprising the emitters is called source. Note that a measurement setup with a source with multiple emitters and a listener with multiple receivers has already been considered [19]⁠.

	In typical [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] measurements, only the direction of the incoming signal is varied. In more recent setups also different sound-ear distances have been considered [4], [11], [20]⁠. However, sometimes the variation of other parameters is of interest. For example, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] were measured as a function of the head orientation relative to the torso [21]⁠, or the room IRs were measured as a function of the room temperature [22]⁠. An [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] file format should thus consider even such parameters.		In typical [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] measurements, only the direction of the incoming signal is varied. In more recent setups also different sound-ear distances have been considered [4], [11], [20]⁠. However, sometimes the variation of other parameters is of interest. For example, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] were measured as a function of the head orientation relative to the torso [21]⁠, or the room IRs were measured as a function of the room temperature [22]⁠. An [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] file format should thus consider even such parameters.


	== Aim of SOFA ==		== Aim of SOFA ==

Isfmiho at 06:54, 22 May 2013

2013-05-22T06:54:28Z

← Older revision		Revision as of 08:54, 22 May 2013
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	* Predefined description conventions for the most common measurement setups.		* Predefined description conventions for the most common measurement setups.

	[[SOFA Specifications]] aim at fulfilling all those requirements. In a nutshell, the measurement setup is described by various objects and their relations. The information is stored in a numeric container based on [[netCDF-4]]. We consider a measurement as a discrete sampled observation done at a specific time and under a specific condition. Each measurement consists of data (e.g., an [http://en.wikipedia.org/wiki/Impulse_response impulse response, IR]) and is described by its corresponding dimensions and metadata. All measurements are stored in a single data structure (e.g., a matrix of IRs). A consistent description of measurement setups are given by [[SOFA conventions]].		[[SOFA Specifications]] aim at fulfilling all those requirements. In a nutshell, the measurement setup is described by various objects and their relations. The information is stored in a numeric container based on [http://en.wikipedia.org/wiki/NetCDF netCDF-4]. We consider a measurement as a discrete sampled observation done at a specific time and under a specific condition. Each measurement consists of data (e.g., an [http://en.wikipedia.org/wiki/Impulse_response impulse response, IR]) and is described by its corresponding dimensions and metadata. All measurements are stored in a single data structure (e.g., a matrix of IRs). A consistent description of measurement setups are given by [[SOFA conventions]].

	== Other existing data formats ==		== Other existing data formats ==

Ente: Protected "General information on SOFA" (‎[edit=sysop] (indefinite) ‎[move=sysop] (indefinite))

2013-05-21T12:13:41Z

Protected "General information on SOFA" (‎[edit=sysop] (indefinite) ‎[move=sysop] (indefinite))

← Older revision	Revision as of 14:13, 21 May 2013
(No difference)

Isfmiho at 13:06, 17 May 2013

2013-05-17T13:06:47Z

← Older revision		Revision as of 15:06, 17 May 2013
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	== Typical measurement setups ==		== Typical measurement setups ==

	One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] were those of a dummy-head microphone measured in an anechoic room [1]. Two microphones placed at the ear simulators were used for the recordings and one loudspeaker was used for the signal excitation. The loudspeaker was moved to the desired elevation and the mannequin was rotated to the desired azimuth. Taken together, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] for 710 spatial positions were measured at elevations from -40° to +90° in steps of 10° and 360° azimuthal range in steps of 5° and a constant distance of 1.4 m. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are provided as [http://en.wikipedia.org/wiki/Impulse_response impulse responses (IRs)] with the length of 512 samples at a sampling rate of 44.1 kHz.		One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] were those of a [http://en.wikipedia.org/wiki/Dummy_head_recording dummy-head] microphone measured in an anechoic room [1]. Two microphones placed at the ear simulators were used for the recordings and one loudspeaker was used for the signal excitation. The loudspeaker was moved to the desired elevation and the mannequin was rotated to the desired azimuth. Taken together, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] for 710 spatial positions were measured at elevations from -40° to +90° in steps of 10° and 360° azimuthal range in steps of 5° and a constant distance of 1.4 m. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are provided as [http://en.wikipedia.org/wiki/Impulse_response impulse responses (IRs)] with the length of 512 samples at a sampling rate of 44.1 kHz.

	One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] measured in human listeners was the CIPIC database [2]⁠. The measurements were performed at a constant distance of 1 m for 1250 spatial directions around the listener. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are available for 43 listeners as IRs of 200 samples at a sampling rate of 44.1 kHz. Since then many other [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIR databases have been made publicly available [3–8]⁠.		One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] measured in human listeners was the CIPIC database [2]⁠. The measurements were performed at a constant distance of 1 m for 1250 spatial directions around the listener. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are available for 43 listeners as IRs of 200 samples at a sampling rate of 44.1 kHz. Since then many other [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIR databases have been made publicly available [3–8]⁠.

Isfmiho at 13:03, 17 May 2013

2013-05-17T13:03:45Z

← Older revision		Revision as of 15:03, 17 May 2013
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	[http://en.wikipedia.org/wiki/Head-related_transfer_function Head-related transfer functions (HRTFs)] describe the spatial filtering of the incoming sound due to the listener's anatomy. [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are crucially important for the binaural reproduction of virtual acoustics. [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] have been measured by a number of laboratories and are typically stored in each lab's native file format. While the different formats are of advantage for each lab, an exchange of such data is difficult due to incompatibilities between formats.		[http://en.wikipedia.org/wiki/Head-related_transfer_function Head-related transfer functions (HRTFs)] describe the spatial filtering of the incoming sound due to the listener's anatomy. [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are crucially important for the binaural reproduction of virtual acoustics. [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] have been measured by a number of laboratories and are typically stored in each lab's native file format. While the different formats are of advantage for each lab, an exchange of such data is difficult due to incompatibilities between formats.

	The '''spatially oriented format for acoustics (SOFA)''' aims at representing spatial data in a general way, allowing to store not only [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] but also more complex data, e.g., directional room impulse responses (DRIRs) measured with a multichannel microphone array excited by a loudspeaker array. In order to simplify the adaption of SOFA for various applications, examples of implementation of the format specifications are provided together with a collection of exemplary data sets converted to SOFA.		The '''spatially oriented format for acoustics (SOFA)''' aims at representing spatial data in a general way, allowing to store not only [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] but also more complex data, e.g., [http://en.wikipedia.org/wiki/Impulse_response directional room impulse responses] (DRIRs) measured with a multichannel microphone array excited by a loudspeaker array. In order to simplify the adaption of SOFA for various applications, examples of implementation of the format specifications are provided together with a collection of exemplary data sets converted to SOFA.

	== Typical measurement setups ==		== Typical measurement setups ==

	One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] were those of a dummy-head microphone measured in an anechoic room [1]. Two microphones placed at the ear simulators were used for the recordings and one loudspeaker was used for the signal excitation. The loudspeaker was moved to the desired elevation and the mannequin was rotated to the desired azimuth. Taken together, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] for 710 spatial positions were measured at elevations from -40° to +90° in steps of 10° and 360° azimuthal range in steps of 5° and a constant distance of 1.4 m. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are provided as impulse responses (IRs) with the length of 512 samples at a sampling rate of 44.1 kHz.		One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] were those of a dummy-head microphone measured in an anechoic room [1]. Two microphones placed at the ear simulators were used for the recordings and one loudspeaker was used for the signal excitation. The loudspeaker was moved to the desired elevation and the mannequin was rotated to the desired azimuth. Taken together, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] for 710 spatial positions were measured at elevations from -40° to +90° in steps of 10° and 360° azimuthal range in steps of 5° and a constant distance of 1.4 m. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are provided as [http://en.wikipedia.org/wiki/Impulse_response impulse responses (IRs)] with the length of 512 samples at a sampling rate of 44.1 kHz.

	One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] measured in human listeners was the CIPIC database [2]⁠. The measurements were performed at a constant distance of 1 m for 1250 spatial directions around the listener. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are available for 43 listeners as IRs of 200 samples at a sampling rate of 44.1 kHz. Since then many other [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIR databases have been made publicly available [3–8]⁠.		One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] measured in human listeners was the CIPIC database [2]⁠. The measurements were performed at a constant distance of 1 m for 1250 spatial directions around the listener. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are available for 43 listeners as IRs of 200 samples at a sampling rate of 44.1 kHz. Since then many other [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIR databases have been made publicly available [3–8]⁠.
Line 30:		Line 30:
	* Predefined description conventions for the most common measurement setups.		* Predefined description conventions for the most common measurement setups.

	[[SOFA Specifications]] aim at fulfilling all those requirements. In a nutshell, the measurement setup is described by various objects and their relations. The information is stored in a numeric container based on [[netCDF-4]]. We consider a measurement as a discrete sampled observation done at a specific time and under a specific condition. Each measurement consists of data (e.g., an impulse response, IR) and is described by its corresponding dimensions and metadata. All measurements are stored in a single data structure (e.g., a matrix of IRs). A consistent description of measurement setups are given by [[SOFA conventions]].		[[SOFA Specifications]] aim at fulfilling all those requirements. In a nutshell, the measurement setup is described by various objects and their relations. The information is stored in a numeric container based on [[netCDF-4]]. We consider a measurement as a discrete sampled observation done at a specific time and under a specific condition. Each measurement consists of data (e.g., an [http://en.wikipedia.org/wiki/Impulse_response impulse response, IR]) and is described by its corresponding dimensions and metadata. All measurements are stored in a single data structure (e.g., a matrix of IRs). A consistent description of measurement setups are given by [[SOFA conventions]].

	== Other existing data formats ==		== Other existing data formats ==

Isfmiho at 13:01, 17 May 2013

2013-05-17T13:01:11Z

Petibub at 12:34, 17 May 2013

2013-05-17T12:34:43Z

← Older revision		Revision as of 14:34, 17 May 2013
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	In typical HRTF measurements, only the direction of the incoming signal is varied. In more recent setups also different sound-ear distances have been considered [4], [11], [20]⁠. However, sometimes the variation of other parameters is of interest. For example, HRTFs were measured as a function of the head orientation relative to the torso [21]⁠, or the room IRs were measured as a function of the room temperature [22]⁠. An HRTF file format should thus consider even such parameters.		In typical HRTF measurements, only the direction of the incoming signal is varied. In more recent setups also different sound-ear distances have been considered [4], [11], [20]⁠. However, sometimes the variation of other parameters is of interest. For example, HRTFs were measured as a function of the head orientation relative to the torso [21]⁠, or the room IRs were measured as a function of the room temperature [22]⁠. An HRTF file format should thus consider even such parameters.

	== ~~What~~ ~~SOFA~~ ~~provides~~ ==		== Aim of SOFA ==

	While designing SOFA, we set up the following requirements:		While designing SOFA, we set up the following requirements:

Petibub: Petibub moved page More general information on SOFA to General information on SOFA

2013-05-17T09:27:50Z

Petibub moved page More general information on SOFA to General information on SOFA

← Older revision	Revision as of 11:27, 17 May 2013
(No difference)

Petibub: /* What SOFA provides */

2013-05-17T09:24:28Z

What SOFA provides

← Older revision		Revision as of 11:24, 17 May 2013
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	* Predefined description conventions for the most common measurement setups.		* Predefined description conventions for the most common measurement setups.

	[[SOFA ~~specifications~~]] aim at fulfilling all those requirements. In a nutshell, the measurement setup is described by various objects and their relations. The information is stored in a numeric container based on [[netCDF-4]]. We consider a measurement as a discrete sampled observation done at a specific time and under a specific condition. Each measurement consists of data (e.g., an impulse response, IR) and is described by its corresponding dimensions and metadata. All measurements are stored in a single data structure (e.g., a matrix of IRs). A consistent description of measurement setups are given by [[SOFA conventions]].		[[SOFA Specifications]] aim at fulfilling all those requirements. In a nutshell, the measurement setup is described by various objects and their relations. The information is stored in a numeric container based on [[netCDF-4]]. We consider a measurement as a discrete sampled observation done at a specific time and under a specific condition. Each measurement consists of data (e.g., an impulse response, IR) and is described by its corresponding dimensions and metadata. All measurements are stored in a single data structure (e.g., a matrix of IRs). A consistent description of measurement setups are given by [[SOFA conventions]].



	== Other existing data formats ==		== Other existing data formats ==

← Older revision		Revision as of 15:01, 17 May 2013
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	== General ==		== General ==

	Head-related transfer functions (HRTFs) describe the spatial filtering of the incoming sound due to the listener's anatomy. HRTFs are crucially important for the binaural reproduction of virtual acoustics. HRTFs have been measured by a number of laboratories and are typically stored in each lab's native file format. While the different formats are of advantage for each lab, an exchange of such data is difficult due to incompatibilities between formats.		[http://en.wikipedia.org/wiki/Head-related_transfer_function Head-related transfer functions (HRTFs)] describe the spatial filtering of the incoming sound due to the listener's anatomy. [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are crucially important for the binaural reproduction of virtual acoustics. [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] have been measured by a number of laboratories and are typically stored in each lab's native file format. While the different formats are of advantage for each lab, an exchange of such data is difficult due to incompatibilities between formats.

	The '''spatially oriented format for acoustics (SOFA)''' aims at representing spatial data in a general way, allowing to store not only HRTFs but also more complex data, e.g., directional room impulse responses (DRIRs) measured with a multichannel microphone array excited by a loudspeaker array. In order to simplify the adaption of SOFA for various applications, examples of implementation of the format specifications are provided together with a collection of exemplary data sets converted to SOFA.		The '''spatially oriented format for acoustics (SOFA)''' aims at representing spatial data in a general way, allowing to store not only [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] but also more complex data, e.g., directional room impulse responses (DRIRs) measured with a multichannel microphone array excited by a loudspeaker array. In order to simplify the adaption of SOFA for various applications, examples of implementation of the format specifications are provided together with a collection of exemplary data sets converted to SOFA.

	== Typical measurement setups ==		== Typical measurement setups ==

	One of the first publicly available HRTFs were those of a dummy-head microphone measured in an anechoic room [1]. Two microphones placed at the ear simulators were used for the recordings and one loudspeaker was used for the signal excitation. The loudspeaker was moved to the desired elevation and the mannequin was rotated to the desired azimuth. Taken together, HRTFs for 710 spatial positions were measured at elevations from -40° to +90° in steps of 10° and 360° azimuthal range in steps of 5° and a constant distance of 1.4 m. The HRTFs are provided as impulse responses (IRs) with the length of 512 samples at a sampling rate of 44.1 kHz.		One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] were those of a dummy-head microphone measured in an anechoic room [1]. Two microphones placed at the ear simulators were used for the recordings and one loudspeaker was used for the signal excitation. The loudspeaker was moved to the desired elevation and the mannequin was rotated to the desired azimuth. Taken together, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] for 710 spatial positions were measured at elevations from -40° to +90° in steps of 10° and 360° azimuthal range in steps of 5° and a constant distance of 1.4 m. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are provided as impulse responses (IRs) with the length of 512 samples at a sampling rate of 44.1 kHz.

	One of the first publicly available HRTFs measured in human listeners was the CIPIC database [2]⁠. The measurements were performed at a constant distance of 1 m for 1250 spatial directions around the listener. The HRTFs are available for 43 listeners as IRs of 200 samples at a sampling rate of 44.1 kHz. Since then many other HRTF/DRIR databases have been made publicly available [3–8]⁠.		One of the first publicly available [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] measured in human listeners was the CIPIC database [2]⁠. The measurements were performed at a constant distance of 1 m for 1250 spatial directions around the listener. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are available for 43 listeners as IRs of 200 samples at a sampling rate of 44.1 kHz. Since then many other [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIR databases have been made publicly available [3–8]⁠.

	All those measurement setups have the following properties in common. In an anechoic chamber or in a room, excitation signals are generated and microphones are used to record the incoming signals (see Fig. 1). The measurement is repeated while varying the spatial position of the excitation source relative to the listener, which is done by varying the position of the listener, the sound source, or both in different dimensions.		All those measurement setups have the following properties in common. In an anechoic chamber or in a room, excitation signals are generated and microphones are used to record the incoming signals (see Fig. 1). The measurement is repeated while varying the spatial position of the excitation source relative to the listener, which is done by varying the position of the listener, the sound source, or both in different dimensions.
	Binaural HRTF measurement setups use only two microphones to record the left and right ear signals. However, HRTF/DRIRs measurements may also consider multiple microphones, e.g., three microphones per head side in hearing-assist devices [7]⁠, tens of microphones arranged in an array structure at different directions and distances from the center [9]⁠, a multichannel microphone array arranged around the listeners in a reciprocal HRTF measurement system [10], [11]⁠, multichannel microphone arrays for measuring DRIRs [12]⁠ or various microphone positions in a room, e.g., for concert-hall acoustics measurements [13]⁠. As a generalization, microphones and an object comprising those microphones can be identified. Thus, in this article, a microphone as the single receiver of the sound field is called the receiver, and the comprising all the receivers is called the listener, see Fig. 1.		Binaural [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] measurement setups use only two microphones to record the left and right ear signals. However, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF]/DRIRs measurements may also consider multiple microphones, e.g., three microphones per head side in hearing-assist devices [7]⁠, tens of microphones arranged in an array structure at different directions and distances from the center [9]⁠, a multichannel microphone array arranged around the listeners in a reciprocal [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] measurement system [10], [11]⁠, multichannel microphone arrays for measuring DRIRs [12]⁠ or various microphone positions in a room, e.g., for concert-hall acoustics measurements [13]⁠. As a generalization, microphones and an object comprising those microphones can be identified. Thus, in this article, a microphone as the single receiver of the sound field is called the receiver, and the comprising all the receivers is called the listener, see Fig. 1.

	The sound source used for the excitation signal is not necessarily a single point source. Loudspeaker arrays were used, either to control the sound field surrounding the listener, e.g., wave-field synthesis [11], [14], [15]⁠, or higher-order Ambisonics [16], [17]⁠ or to control the radiation characteristics of the sound sources [18]⁠. Similarly to the concept of listener and receivers, in this article, the particular sources creating the excitation signal are called emitters and the object comprising the emitters is called source. Note that a measurement setup with a source with multiple emitters and a listener with multiple receivers has already been considered [19]⁠.		The sound source used for the excitation signal is not necessarily a single point source. Loudspeaker arrays were used, either to control the sound field surrounding the listener, e.g., wave-field synthesis [11], [14], [15]⁠, or higher-order Ambisonics [16], [17]⁠ or to control the radiation characteristics of the sound sources [18]⁠. Similarly to the concept of listener and receivers, in this article, the particular sources creating the excitation signal are called emitters and the object comprising the emitters is called source. Note that a measurement setup with a source with multiple emitters and a listener with multiple receivers has already been considered [19]⁠.

	In typical HRTF measurements, only the direction of the incoming signal is varied. In more recent setups also different sound-ear distances have been considered [4], [11], [20]⁠. However, sometimes the variation of other parameters is of interest. For example, HRTFs were measured as a function of the head orientation relative to the torso [21]⁠, or the room IRs were measured as a function of the room temperature [22]⁠. An HRTF file format should thus consider even such parameters.		In typical [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] measurements, only the direction of the incoming signal is varied. In more recent setups also different sound-ear distances have been considered [4], [11], [20]⁠. However, sometimes the variation of other parameters is of interest. For example, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] were measured as a function of the head orientation relative to the torso [21]⁠, or the room IRs were measured as a function of the room temperature [22]⁠. An [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] file format should thus consider even such parameters.

	== Aim of SOFA ==		== Aim of SOFA ==
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	== Other existing data formats ==		== Other existing data formats ==

	Beside SOFA, HRTFs have been stored using different formats, all of them having advantages and disadvantages. The CIPIC database [2]⁠ provides a file per listener in either a plain text or Matlab (Mathworks, Inc.) file format. The directions are hard coded, i.e., the index of an ~~HRTF~~ corresponds to a predefined direction used in the measurements. While the representation of HRTFs from other directions is not allowed, anthropometric data have been stored within that format. The openDAFF package1, while similarly storing HRTFs only in a regular angular distance, uses a key-value system for the description of the metadata which seems to be very promising. Other databases such as LISTEN [3]⁠ and ARI [6]⁠, consist of an HRTF matrix and additional matrices describing the direction of the corresponding HRTF, thus, allowing to represent HRTFs from any direction. In that formats, HRTFs from each listener are stored in a separate file. In the database storing the HRTFs as a function of distance [4]⁠, the data are stored in a separate file for each distance. Combined with the necessity to store a separate file for each listener, those three latter formats would result in many files. The MARL-NYU database [23]⁠ harmonized the format of CIPIC, LISTEN, MIT, and others databases, and stores all those data in a single file. This concept seems to be promising when combined with a network interface and partial file access in the future. Most of those HRTFs are stored in Matlab formats, i.e., they use a Matlab file convention to store predefined matrices. In contrast, SDIF [24]⁠, a general format for storing audio-related data, has been adapted to HRTFs, allowing to store HRTFs of a single listener in a mixed text-based and binary representation. The concert-hall data [25]⁠, stored as compressed “.wav” files, are another example for a mixed-binary format, which further requires a description (separate text files) in order to being able to interpret the data. The HRTFs measured in rooms (e.g., [8]⁠) are also Matlab files and the relationship between the data and the geometry of the measurement setup is provided in separate publications.		Beside SOFA, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] have been stored using different formats, all of them having advantages and disadvantages. The CIPIC database [2]⁠ provides a file per listener in either a plain text or Matlab (Mathworks, Inc.) file format. The directions are hard coded, i.e., the index of an [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] corresponds to a predefined direction used in the measurements. While the representation of [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] from other directions is not allowed, anthropometric data have been stored within that format. The openDAFF package1, while similarly storing [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] only in a regular angular distance, uses a key-value system for the description of the metadata which seems to be very promising. Other databases such as LISTEN [3]⁠ and ARI [6]⁠, consist of an [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF] matrix and additional matrices describing the direction of the corresponding [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTF], thus, allowing to represent [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] from any direction. In that formats, [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] from each listener are stored in a separate file. In the database storing the [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] as a function of distance [4]⁠, the data are stored in a separate file for each distance. Combined with the necessity to store a separate file for each listener, those three latter formats would result in many files. The MARL-NYU database [23]⁠ harmonized the format of CIPIC, LISTEN, MIT, and others databases, and stores all those data in a single file. This concept seems to be promising when combined with a network interface and partial file access in the future. Most of those [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] are stored in Matlab formats, i.e., they use a Matlab file convention to store predefined matrices. In contrast, SDIF [24]⁠, a general format for storing audio-related data, has been adapted to [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] , allowing to store [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] of a single listener in a mixed text-based and binary representation. The concert-hall data [25]⁠, stored as compressed “.wav” files, are another example for a mixed-binary format, which further requires a description (separate text files) in order to being able to interpret the data. The [http://en.wikipedia.org/wiki/Head-related_transfer_function HRTFs] measured in rooms (e.g., [8]⁠) are also Matlab files and the relationship between the data and the geometry of the measurement setup is provided in separate publications.