JILL ARF files

jrecord stores data in HDF5 files, a hierarchical format that supports a wide range of architectures and data types. It organizes the data in the file according to the ARF specification (see https://github.com/dmeliza/arf). Briefly, this layout is as follows:

• The /jill_log dataset stores log messages from jrecord and from other programs that connect to its 0MQ logging socket.
• Each recording epoch is stored in a sequentially named group, /jrecord_0000, /jrecord_0001, .... These groups (entries in the ARF specification) have a number of attributes:
  • timestamp is a two-element vector containing the unix timestamp (number of seconds and microseconds since Jan 1, 1970 UTC)
  • jack_frame is the frame count at thes start of the entry
  • jack_sampling_rate is the sampling rate of the JACK engine when the entry was created.
  • entry_creator is a string indicating the program that created the file and its version
• Each entry contains datasets that correspond to jrecord ports. Sampled and event data are stored differently (see below). All datasets have attributes that indicate the units and sampling rate of the data.

Sampled data

jrecord stores sampled data in one-dimensional arrays of 32-bit floats, which is how these data are represented in JACK. Values are bounded between -1.0 and 1.0.

Event data

jrecord stores data from event ports in HDF5 datasets using a compound data type. The fields are:

• start: the frame count when the event occurred
• status: the MIDI status byte of the message
• message: a string giving the remainder of the event message. This string may be hex-encoded for some event types and UTF-8 encoded for others.

JILL modules use the following status bytes:

value	explanation	message
0-15	stimulus on	the name of the stimulus, utf-8 encoded string
16-31	stimulus off	the name of the stimulus, utf-8 encoded string
128-143	note on	pitch and velocity, 2 bytes, hex encoded
144-159	note off	pitch and velocity, 2 bytes, hex encoded

At present, jstim emits stimulus on and stimulus off events when it starts and stops playback. jdetect emits note on and note off events when it detects signals starting and stopping. It uses the MIDI default pitch of 60 and velocity of 64.