Glossary
AC Coupled Amplification: Amplification of only AC components of a signal.
The DC component (DC offset) is blocked by a capacitor/resistor network in the
input signal path. AC coupled amplification is the alternative to DC
Coupled Amplification.
Amplitude: Amplitude of a given position in an EOD waveform.
Amplitude is displayed in arbitrary units (not representing voltage of discharge)
intended for comparative purposes only. These values are scaled to a Peak-to-Peak
Amplitude defined by a user-defined Scale
Factor.
Area: Area under the curve of an EOD waveform calculated
as the Integral of Duration
(ms) and Amplitude .
Baseline: the resting amplitude value between successive
EODs. In Pulse-Type Electric
fish the baseline usually (but not always) corresponds to the Zero
Line (0V). In some circumstances there may be a natural DC
Offset to the signal. The baseline may also depart from the zero
line if the digitizing software does not center bipolar signals at 0V (as is the
case for PC99 Files or some
files digitized with DC Coupled Amplification
).
Cubic Spline Interpolation: A procedure for the determination
of intermediate Amplitude and
Duration values between successive
Sample Points in a Data
Array . Cubic Spline Interpolation determines the position of intermediate
points by computing a theoretical curve through sampling points. A cubic spline
is a piecewise cubic polynomial such that the function, its derivative and its
second derivative are continuous at the interpolation nodes. Electric Fish Waveform
Analyzer uses a cubic spline algorithm based on Bezier curves.
Data Array: A vertical column (array) of Sample
Points , each with a specific Amplitude
and a known Sampling Frequency
is the raw data used to plot and analyze EOD waveforms in the Electric
Fish Waveform Analyzer program.
DC Coupled Amplification: Amplification of all components
of a signal down to direct current (0 Hz or “DC”). DC coupled amplification
preserves the DC offset of a signal. DC coupled amplification is the alternative
to AC Coupled Amplification .
DC offset: (DC = direct current). Appears in signal recordings
with DC Coupled Amplification
as a natural departure of the Baseline
of an EOD from the Zero Line
(0V) associated with a slow flow of current through the electric organ
(creating an offset voltage).
Derivative: The derivative of the EOD is computed at
each Sample Point as dy/dx (change
in Amplitude (y) / change in Duration (x)) between that
sampling point and the previous one.
Duration: The duration (in milliseconds, ms) between
two points in an EOD waveform. Electric Fish Waveform Analyzer measures duration
of Phases and Segments
of phases.
Electric Fishes: Fish that generate Weakly
Electric or Strongly Electric
Electric Organ Discharges (EODs).
The most diverse groups of electric fish are the New World Gymnotiform
fishes and the Old World Mormyriform fishes. Other electrogenic fish
groups include the African freshwater catfishes (Malapterus), the marine rays
(Torpedo) and the stargazers (Uranoscopidae).
Electric Organ Discharge (see EOD)
End: The position of the end of the EOD at a user defined
% amplitude (see Analyze Waveform Shape)
of the last Phase.
EOD (= Electric Organ Discharge). The external electric
field generated from the discharge of one or more electric organs in
Electric Fishes . In Pulse-Type
electric fish the terms EOD, EOD waveform and Waveform
refer (in this help system) interchangeably to a single pulse. In Tone-Type
electric fish the terms EOD, EOD waveform and Waveform
refer (in this help system) to a sequence of variable length which
includes at least two positive wave crests and their intervening troughs.
Fourier Power Spectrum: Frequency domain plot showing
the frequency composition of an EOD. Here the horizontal deflection is the frequency
variable and the vertical deflection is the signals amplitude at that frequency.
Frequency is displayed on a linear scale as kHz (kilohertz). Amplitude is displayed
on a logarithmic scale as dB (decibels). Each –3dB attenuation from the
minimum attenuation at 0 dB represents an approximate halving of signal amplitude.
The peak frequency in the Fourier Power Spectrum (scaled to the minimum attenuation
of 0 dB) is the Peak Power Frequency
(PPF ). Fourier Power
Spectra are computed using a 2048-point Fast Fourier Transform (FFT). The FFT
is a mathematical procedure originally developed by the French mathematician John
Baptiste Fourier (1768 – 1830).
Gymnotiform: New World Electric
Fishes of the order Gymnotiformes (Teleostei: Ostariophysi). Weakly
Electric Gymnotiforms are known by many names, e.g.: knife-fishes
[English]; sarapó, itui [Portuguese - Brazil]; macana [Spanish - Peru];
cuchillo [Spanish - Venezuela, Colombia]). The Strongly
Electric gymnotiform, Electrophorus electricus, is known as the
electric eel [English], poraquê [Portuguese – Brazil], anguila electrica
[Spanish], temblador [Spanish-Venezuela].
Integral: Area
under the curve of the EOD Waveform. Integration is based on computing
the area between successive Sample Points
. The area between two samples (above or below the Zero
Line ) is approximated by the sum of the area of:
i. a rectangle between samples bordered at one end by the zero line and at its
opposite end by the lowest amplitude of the two samples.
ii. a right-angled triangle whose hypotenuse forms a straight line between the
sample points and which sits on top of (or below for –ve phases) the rectangle.
Interpolation: Process of determining intermediate position
between a series of Sample Points .
Triangulation Interpolation draws
a straight line between sample points. Cubic
Spline Interpolation draws a curved line between sample points.
Offset: Disparity between amplitude of Baseline
of an EOD waveform and the Zero Line
(true 0 volts).
P1: The dominant positive Phase
of a Pulse-Type EOD
plotted with head positivity upwards. P1 can also be applied to the dominantly
positive component of a Tone-Type
EOD.
P1 + P2 Amplitude: Amplitude difference between Peak
Amplitude of Phases
P1 and P2.
PC99 Files: Files that were digitized and saved in .prn
(Lotus TM) format using the Amplicon PC99 TM Analog-Digital acquisition hardware
and software. Any column-arranged array of amplitude readings recorded at a known
Sampling Frequency can be converted
to PC99 file format using a text editor or spreadsheet program using the file
format described in PC99 Files.
Peak Amplitude: Maximum amplitude of a given Phase
of an EOD.
Peak Power Frequency: (PPF). The Frequency in the Fourier
Power Spectrum of an EOD with the greatest amplitude value. PPF
is scaled to the minimum attenuation of 0 dB.
Peak-to-Peak Amplitude Difference between positive and
negative Peak Amplitude of greatest
values in an EOD waveform.
Phase: Positive or Negative component of EOD waveform
separated by Zero Crossovers. EOD waveforms of gymnotiforms comprise 1 –
6 phases of alternating polarity. The Duration
, Amplitude and Area
of each phase is variable.
PPF: = Peak Power
Frequency of Fourier Power Spectrum of an EOD waveform.
Pulse-Type (EODs/Electric Fishes): EODs comprising
a train of discrete pulses separated by silence. Gymnotiform
fishes of the families Gymnotidae, Hypopomidae and Rhamphichthyidae
generate Pulse-Type EODs. Pulse-Type EODs of gymnotiform fishes comprise from
1 (monophasic) to 6 (multiphasic) Phases
of alternating polarity.
Sample Points: Points in an EOD waveform that represent a discrete amplitude recorded
during the digitization of the EOD. In an EOD digitized at a Sampling Frequency
of 100 kHz (100,000 sample points per second), the time interval separating successive
sample points is 1/100,000 = 0.00001 s or 0.01 ms. A vertical column (array) of
sample points, each with a specific amplitude and a known sampling frequency is
the raw data used to plot and analyze EOD waveforms in the Electric Fish Waveform
Analyzer program. Electric Fish Waveform
Analyzer operates with a Data Array of 2048
sample points (i.e. 2048 rows of amplitude values).
Sampling Frequency: (also known as sampling rate): The
number of Sample Points recorded
per unit time by the digitizing device used to record an EOD. In an EOD digitized
at a sampling frequency of 100 kHz (100,000 sample points per second), the time
interval separating successive sample points is 1/100,000 = 0.00001 s or 0.01
ms.
Sampling Resolution: Resolution of digitised signal in Bits (usual sampling resolutions
are 8-bit, 12-bit, 16-bit, 24-bit and 32-bit. The vertical deflection of a signal
recorded with 8-bit resolution is represented by only 256 points. With 12-bot
resolution this rises to 1024 points. With higher resolutions each sampling point
is measured very accurately. With lower resolutions, the measurements are less
exact and gentle curves adopt a step-like structure.
Segment: Homologous sections of the Waveform of an EOD
following a three-step process of subdivision: 1, separation of up to 5 Phases
(P-1, P0, P1 , P2,
P3 in strict chronological order) at Zero Crossovers
, where P1 is the dominant positive phase in EODs plotted with head-positivity
upwards; 2, division of each EOD phase at the phase peak (Peak
Amplitude ) into ascending and descending limbs; 3, division of
each limb by the position of the maximum positive or negative Derivative
value (for ascending and descending phases respectively). Following
this procedure a monophasic EOD will have 4 (1 x 4) segments, a biphasic EOD will
have 8 (2 x 4) segments and a 6-phase EOD will have (6 x 4) 24 segments, etc.
Sound Files: Files that are stored in .txt format compatible
with the commercial sound editing program CoolEdit TM. The Electric Fish Waveform
Analyzing program can convert PC99 Files
to Sound files. Any column-arranged array of amplitude readings recorded
at a known Sampling Frequency can
be converted to sound file format using a text editor or spreadsheet program using
the file format described in: Sound
Files.
Start: The position of the beginning of the EOD at a user
defined % amplitude (see Analyze
Waveform Shape) of the first Phase.
Strongly Electric (EODs
): EODs with a high voltage - usually exceeding 50 V. Strongly
electric EODs are generated by the New World freshwater electric eel Electrophorus
electricus, the African freshwater catfish Malapterus electricus, and the marine
ray Torpedo spp.
Timing: Absolute Time of an event in an EOD Waveform
(relative to the Start of
an EOD ).
Tone-Type (EODs/Electric Fishes): EODs comprising
a continual periodic wave of alternating polarity with no periods of silence.
Gymnotiform fishes of the families
Sternopygidae and Apteronotidae generate Tone-type EODs.
Triangulation Interpolation: A procedure for the determination
of intermediate Amplitude and
Duration between successive
Sample Points in a Data
Array . Triangulation Interpolation determines the position of intermediate
points by plotting a straight line between successive sample points.
Valid Phase: A valid phases is a Phase
where the Peak Amplitude exceeds
the Minimum Peak %. Only
the Duration and Area
of valid phases are computed for data output. Valid phases are marked on
the EOD plot with Peaks.
Invalid phases are not marked.
Waveform: Two-dimensional plot (amplitude on y axis,
time on x axis) of a signal, in this case the Electric
Organ Discharge (EOD) of an Electric
Fish. Used also to refer to the entire array of Sample Points characterizing
a digitized signal (including electrical silence flanking the EOD).
Weakly Electric (EODs):EODs
with a low voltage (usually less than 1 volt), which cannot be felt but are easily
detected and recorded with submerged electrodes and an amplifier. Weakly electric
EODs are generated by all New World Gymnotiformes except the strongly electric
eel Electrophorus electricus, and all Old World Mormyriformes. All fishes generating
weakly electric EODs are from freshwaters.
Zero Crossover: The zero volt (arbitrary amplitude value
= 0) boundary between two successive Phases
of an EOD.
Zero Line: Line representing a true voltage value of zero
(displayed in Electric Fish Waveform Analyzer as an arbitrary amplitude value
of zero). The Baseline of an EOD may be Offset
from the Zeroline.