|1||Sample Y From Channel 1||[0..1]||NM|
|2||Sample Y From Channel 2||[0..1]||NM|
|3||Sample Y From Channel 3||[0..1]||NM|
|4||Sample Y From Channel 4||[0..1]||NM|
Components: <Sample Y From Channel 1 (NM)> & <Sample Y From Channel 2 (NM)> & <Sample Y From Channel 3 (NM)> & <Sample Y From Channel 4 (NM)>
Definition: This data type is used to represent channel-multiplexed waveform data. Assuming that fields that utilize this data type repeat and that Y represents the specific repetition, the components of the repetition will reflect sample Y from each channel.
Usage Note: The MA data type is preferred when the signal recording device outputs the waveform data by time (all signal amplitudes at time sample 1, followed by all signal amplitudes at time sample 2, followed by all signal amplitudes at time sample 3, etc.). The typical count is 32, 64, or 128 channels. At the time of this writing, the MA data type is the one used by most commercial EEG instruments, while other electrophysiological instruments (such as evoked potential instruments) may use the NA data type. The MA data type is the "natural" one for multi-channel EEG instruments since the signal acquisition process involves digitizing each channel in succession as rapidly as possible, then after a fixed interval (like 0.004 seconds) digitizing all the channels again in succession, and repeating this every 0.004 seconds as long as the recording continues.
Conversion of one format to another is often not possible or desirable in near-real-time applications. For example, a long-term EEG recording may go on for 24, 48, 72, or more hours and implementations cannot wait until the recording is ended to transmit the data because physicians need to review the waveforms as the recording is in progress; this is why it only makes sense to organize the data by the MA data type which sends the data one time sample after the next.
Note that, visually, the NA and MA data types are indistinguable: they both appear as a series of numeric components. They are distinguished by context, particularly when used in OBX.5 where the data type is specified in OBX.3.
Use Case: Commercial EEG instruments
Example 1: 3 channels (identical), 6 time-samples
Example 2: 1 channel, 11 time-samples