Stable SOFA Conventions

Free-field HRTF measurement of a single listener (SimpleFreeFieldHRIR)

This conventions essentially defines the setup used in the ARI, LISTEN, FIU, CIPIC, and other similar HRTF databases (Fig. 2). The measurements are done at a constant distance in free field with a single excitation source assuming an omnidirectional loudspeaker. Human listeners are considered and thus, the number of receivers is two. Azimuth and elevation angles are varied and the tilt of the head is not considered during the measurement. The measured HRTFs are represented as FIR filters, with a single HRTF set of a listener per file. The SOFA conventions SimpleFreeFieldHRIR defines such a setup. It requires: General attributes: SOFAConventions: SimpleFreeFieldHRIR, Datatype: FIR, RoomType: free field, other general attributes... Data: The number of receivers is two, thus, the size of Data.IR is [M 2 N]. Only a single sampling rate for the file is allowed, thus SamplingRate is a scalar. Source: Source is in the origin of the setup and consists of a single emitter. SourcePosition: (0 0 0), SourceUp: (0 0 1), SourceView: (1 0 0), SourceRotation, and EmitterPosition: (0 0 0).

• Listener: The listener is in the measurement distance X (in meter) from the source, facing the source. ListenerPosition: (X 0 0), ListenerView: (0 0 0), ListenerUp: (X 0 1).
• Receivers: Two receivers (=ears) on a head with radius H (in meter): ReceiverPosition: (0 -H 0; 0 +H 0).
• The different azimuth and elevation angles of the measurement are described by the ListenerRotation as [M 3] matrix (in degrees). The coordinate type is “din9300”.

The corresponding CDL file is provided in the Conventions directory of the SOFA package.

Microphone-array measurement in a single room (SingleRoomDRIR)

This conventions defines a setup used for measuring DRIRs in a single room with an arbitrary number of receivers (Fig. 4). The setup considers measurements in a room with a single excitation source and a microphone array with an arbitrary number of omnidirectional microphones (i.e., receivers). Because of the special interest in spherical microphone arrays for DRIR measurement, the spherical coordinate system is considered for the description of the receivers. The positions of both the source and the listener are considered as variant. The DRIRs are represented as FIR filters for a single room per file. SingleRoomDRIR consists of:

• General metadata: SOFAConventions: SingleRoomDRIR, Datatype: FIR, RoomType: freefield with a mandatory attribute RoomDescription.
• Data: The amount of the receivers varies, thus, the size of Data.IR is [M R N]. Only one sampling rate is allowed, thus SamplingRate is [1] (in Hz).
• Source: The position and the orientation of the source may vary by providing SourcePosition, SourceUp, SourceView. The coordinate type is cartesian and unit is meter.
• Emitters: Source consists of a single omnidirectional emitter, which position is fixed, EmitterPosition: (0 0 0). EmitterUp and * EmitterView are omitted.
• Listener: Position and the orientation of the listener vary and thus ListenerPosition, ListenerView, and ListenerUp are mandatory. The coordinate type is cartesian and unit is meter.
• Receivers: the position of all receivers via ReceiverPosition is provided. The coordinate type is spherical and unit is “degrees, degrees, meter”. The receivers are considered to be omnidirectional, thus, ReceiverUp and ReceiverView are omitted.
• An additional rotation of the listener is not considered, thus, ListenerRotation is not provided.
• For each measurement, an ID and the time stamp is considered, with MeasurementID as [M] and MeasurementTimeCreated as [M].

The corresponding CDL file is provided in the “Conventions” directory of the SOFA package.