Multiple Reference Signals¶

Version 0.2.0 improves support for files containing more than one reference-signal channel.

In openhdemg, reference signals are stored in:

emgfile["REF_SIGNAL"]

REF_SIGNAL is a pandas DataFrame. Each column is one reference-signal channel.

Common examples include:

force and torque recorded together;
multiple force transducers;
target force and measured force;
original and processed reference traces kept in the same file.

Inspect Reference-Signal Channels¶

import openhdemg.library as emg

emgfile = emg.emg_from_samplefile()

print(emgfile["REF_SIGNAL"].head())
print(emgfile["REF_SIGNAL"].columns)

The sample file contains one reference-signal column named 0, but your imported file can contain more columns.

Rename Columns¶

REF_SIGNAL columns can be named either with base-0 integers, such as 0, 1, 2, or with strings, such as "force" and "target".

String names can make analysis scripts easier to read:

emgfile["REF_SIGNAL"] = emgfile["REF_SIGNAL"].rename(
    columns={
        0: "force",
        1: "target",
    }
)

However, integer-based column names can make interaction with the openhdemg software more straightforward, because channel selection is often naturally expressed as channel 0, channel 1, and so on.

Therefore, this is mostly a personal preference:

use string names if you prefer readability in Python scripts;
use base-0 integer names if you prefer simpler interaction with the openhdemg software or want to keep the file closer to the default openhdemg structure.

`refsig_channel` and `refsig_channels`¶

There are two related argument names.

Use refsig_channel when a function needs one reference signal:

selecting an interval with showselect();
plotting one reference channel;
calculating MVC, RFD, thresholds, discharge-rate properties, and basic MU properties;
showing the reference signal in tracking GUIs.

Use refsig_channels when a function can modify one or more reference signals:

filtering reference signals with filter_refsig();
removing offsets with remove_offset().

Plot One Reference Signal¶

import openhdemg.library as emg

emg.plot_refsig(
    emgfile=emgfile,
    refsig_channel="force",
)

With integer column names:

emg.plot_refsig(
    emgfile=emgfile,
    refsig_channel=0,
)

Add One Reference Signal to MU Plots¶

Most MU plots can add one selected reference signal.

emg.plot_idr(
    emgfile=emgfile,
    addrefsig=True,
    refsig_channel="force",
)

Filter Selected Reference Channels¶

Filter one channel:

filtered = emg.filter_refsig(
    emgfile=emgfile,
    order=4,
    cutoff=15,
    refsig_channels=["force"],
)

Filter more than one channel:

filtered = emg.filter_refsig(
    emgfile=emgfile,
    order=4,
    cutoff=15,
    refsig_channels=["force", "target"],
)

Only the selected channels are modified. Other REF_SIGNAL columns are preserved.

Remove Offset From Selected Channels¶

Automatically remove the offset using the first 1024 samples:

offset_removed = emg.remove_offset(
    emgfile=filtered,
    auto=1024,
    refsig_channels=["force"],
)

Apply the same manual offset to multiple channels:

offset_removed = emg.remove_offset(
    emgfile=filtered,
    offsetval=2.5,
    refsig_channels=["force", "target"],
)

Apply different offsets to different channels:

offset_removed = emg.remove_offset(
    emgfile=filtered,
    offsetval=[2.5, 1.0],
    refsig_channels=["force", "target"],
)

The length of offsetval must match the length of refsig_channels when different offsets are passed.

Resize Using a Selected Reference Channel¶

resized_emgfile, start_, end_ = emg.resize_emgfile(
    emgfile=emgfile,
    how="ref_signal",
    refsig_channel="force",
)

If you already know the sample range:

resized_emgfile, start_, end_ = emg.resize_emgfile(
    emgfile=emgfile,
    area=[12000, 50000],
)

Calculate Force-Based Metrics¶

Use the channel representing the signal of interest.

mvc = emg.get_mvc(
    emgfile=emgfile,
    how="all",
    refsig_channel="force",
)

Analyse MU Properties With One Reference Channel¶

properties = emg.basic_mus_properties(
    emgfile=emgfile,
    mvc=634,
    refsig_channel="force",
)

The selected channel is used for recruitment and derecruitment thresholds, steady-state region selection, and related reference-signal calculations.