
glossary

A list of baudline related digital signal processing acronyms, definitions,
and terms.
Alaw
Audio codec companding format. A logarithmic mapping between 8 bit data
space and 13 bit sample space as described in the CCITT G.711
recommendation. Alaw has 13 bits of dynamic range (78 dB).
See ulaw.
AC
Alternating Current. Power line transmission frequency is either 50 Hz
or 60 Hz depending on global location.
ADC
Analog to Digital Converter. Also known as an A/D (A to D).
The audio card's ADC connects to the
Input Devices window.
ADPCM
Adaptive Differential Pulse Code Modulation. A lossy
CBR audio compression codec. Sample coding can range
from 2 to 5 bits per sample depending on the standard/mode.
AGC
Automatic Gain Control. Adjust the input gain automatically so that
clipping overload is avoided and optimal ENOB bit usage is
achieved. Also see the AGC channel mapping
spaces.
aliasing
Frequency folding. Mirror images of wrapped frequency.
Decimation without proper filtering causes aliasing
which irreversibly corrupts the signal. An antialiasing filter
(LPF) prevents aliasing. To experiment with the
effects of aliasing see the
antialias filter option in the
Input Devices window.
See Nyquist sampling theorem.
AM
Amplitude Modulation.
AM has a carrier frequency and two sidebands (LSB and USB).
See the modulation option in the
Tone Generator window.
ASK
Amplitude Shift Keying. A data modulation scheme that involves
changing the amplitude of a carrier frequency. See AM
and CW.
AWGN
Additive White Gaussian Noise. Also known as WGN. Constant spectral
energy at all frequencies with a probability histogram that follows a Gaussian
bell shaped curve. See the Function option in the
Tone Generator window.
baseband
A signal that is centered around zero Hz.
Both real and complex quadrature signals can be mixed
to baseband. The operation is performed by a
DDC.
For frequency limits see Nyquist.
BER
Bit Error Rate. A measure of data loss.
BPM
Beats Per Minute. A measure of tempo.
bpp
Bits Per Pixel. Color resolution. Common color depths for video
displays are 8, 16, 24, and 32 bpp. 16 bpp is (565)
RGB.
BPSK
Binary Phase Shift Keying. A data modulation scheme that involves
changing the phase of a carrier frequency. BPSK uses 2 distinct phases
(0° and 180°) for 1 bit per symbol. See PSK.
CBR
Constant Bit Rate.
Less efficient than VBR but easier to implement in fixed
data stream applications.
CDMA
Code Division Multiple Access.
CMY
Cyan Magenta Yellow. CMY is a color space rotation of
RGB. See the
RGB mapping menu in the Color
Picker window.
codec
COmpressor DECompressor. A lossy or lossless method of reducing
the data bandwidth. Here is a list of different audio codecs that
baudline supports:
CW
Continuous Wave. Morse code.
DAC
Digital to Analog Converter. Also known as a D/A (D to A).
The Output Devices window connects
to the audio card's DAC.
DAQ
Data acQuisition. The collection and/or generation of signal.
See ADC and DAC.
dB
Decibel. Tenth of a Bell. A logarithmic ratio of powers or
voltages. For power dB = 10 * log10(P2 / P1); For voltage
dB = 20 * log10(V2 / V1); It can be an absolute level when used with a
0 dB reference point or it can be a relative difference measurement.
Each sample bit contributes 6 dB of dynamic range. 16bit samples have
96 dB of dynamic range while 24bit samples have 144 dB of dynamic range.
True real world values are usually much less, see ENOB.
DC
Direct Current. Constant voltage can be seen as a DC offset in the
frequency domain as a peak at 0 Hz.
DDC
Digital Down Converter. Tuner.
Mix a signal down to baseband.
A DDC operates in the complex domain and consists of a frequency
mixer, a LPF, and a
decimator. See the
down mixer in the Input Device window.
decimation
A decimator reduces the sample rate by discarding samples.
It is important to low pass filter in order to prevent
aliasing.
DSB
Double SideBand. See SSB
DSP
Digital Signal Processing. The art of manipulating signals in the
discrete digital domain.
DTMF
Dual Tone Multi Frequency. Telephone signaling tones.
DUT
Device Under Test. Black box. Input a stimulus signal such as
a pure sine wave, linear swept sine, or WGN to the DUT and
then measure the output characterization signal.
ELF
Extremely Low Frequency. 30  300 Hz.
endian
Big and Little Endian. The ordering of 8bit bytes within larger data
structures such as shorts, ints, longs, floats, and doubles. See the
"decode format" in the
Raw Parameters window and the
"flip endian" operation in the
Channel Mapping window.
ENOB
Effective Number of Bits.
Calculated from SINAD.
Describes the quality of an ADC in terms of bits.
See the ENOB measurement window.
FDM
Frequency Division Multiplexing. Interleave channels in frequency.
Like a traditional AM or FM radio.
FEC
Forward Error Correction. Improve the BER by encoding
redundant data that can be used to fix bit errors.
FFT
Fast Fourier Transform. A mathematical operation that converts between
the time and the frequency domains. O(n * log n).
FIFO
First In First Out. An abstract streaming buffer mechanism that is useful
for realtime data processing.
See "man mkfifo" and stdin.
FIR
Finite Impulse Response filter. Performs convolution in the time
domain. A DSP algorithmic construct made up of cascaded
MAC units and filter taps. FIR filters are stable and
have linear phase. Both the decimator in
Input Devices and
Hilbert filters are implemented with FIR filters.
FM
Frequency Modulation.
See the modulation option in the
Tone Generator window.
FPS
Frames Per Second. The higher the frame rate the smoother the
animation or scrolling. See "video FPS" in the
Stats window.
FSK
Frequency Shift Keying. A data modulation scheme that involves switching
between two frequencies called Mark and Space for 1 bit per symbol.
FSK8 would use 8 tones for 3 bits per symbol.
full duplex
Simultaneous transmission of information in two directions. Transmit and
receive. Baudline runs in the full duplex mode when recording a channel
and using the Tone Generator
at the same time. Most Linux audio drivers can be used full
duplex. See half duplex.
GPS
Global Positioning System. Not just an accurate method of determining
position, but also an accurate source of time since each GPS satellite has
an atomic clock. GPS time is locked to UTC time plus
an offset since GPS time does not account for leap seconds. GPS timing
receivers have a digital time code data port and a PPS line
for high accuracy synchronization.
GSM
Groupe Speciale Mobile or Global System for Mobile Communications.
GSM 6.10 is a lossy CBR audio compression codec which has
an audio sample rate of 8000 samples/second and a data rate of 13 Kbps.
GSM is also a popular global mobile phone standard.
half duplex
The transmission of information in only one direction at a time.
Transmit or receive. Baudline is in half duplex when it is in the
record or play run modes. Many of
the original PC sound cards could only operate in half duplex. See
full duplex.
heterodyne
Mix a signal with a sinusoid to move it in frequency space.
Used by radio tuners. See DDC.
Hilbert
A transform that performs a 90° phase shift. Typically implemented
with a FIR filter that has all the odd taps being
zero. Useful for creating complex quadrature
signals. See the "Hilbert"
operation in the Channel Mapping
window.
HPF
High Pass Filter.
Frequencies lower than the cutoff frequency are attenuated.
A HPF coupled with a LPF is a bandpass filter.
See the "HPF" slider control in the Play Deck
window.
Hz
Hertz. Cycles per second. A unit of frequency. Limits are
defined by the Nyquist sampling theorem. Complex
quadrature signals can have negative frequencies.
IF
Intermediate Frequency. The output of a mixer.
IMD
InterModulation Distortion. A twotone signal source modulates together
to create sum and difference frequencies. Second, third, and higher
order products can be present as distortion noise.
interpolation
An interpolator increases the sample rate by inserting zeros in between
samples. It is important to low pass filter in order
to prevent aliasing.
LNA
Low Noise Amplifier. The noise power is proportional to temperature
(degrees Kelvin).
LPF
Low Pass Filter.
Frequencies higher than the cutoff frequency are attenuated.
LPF's are useful for antialiasing in
decimators.
They are also useful for bandpass filtering.
See the "LPF" slider control in the Play Deck
window.
LSB
Dual definitions: Least Significant Bit and Lower SideBand.
For Least Significant Bit see the "1 bit binary decode format" in the
Raw Parameters window and the
"bit reverse" operation in the
Channel Mapping window. Lower side band is frequency inverted around
the carrier frequency, see USB.
MAC
Multiply Accumulate operation. A += B[x] * C[x];
An important building block used internally by many DSP algorithms.
MFSK
Multi Frequency Shift Keying. A data modulation scheme that involves
coding frequency combinations with bits. A variation of
FSK but with more than two frequencies and there can be
more than one frequency active at a time in a parallel fashion.
modem
MOdulator DEModulator. Communications device. A method of
transmitting and receiving digital binary data over an analog channel.
See modulation.
modulation
The process of encoding binary data or waveform information for analog
transmission. Opposite of demodulation.
Here is a list of different modulation types:
mixer
Dual definitions: /dev/mixer for adjusting the gain of a soundcard and
a frequency mixer (multiplication) for a DDC type operation.
MSB
Most Significant Bit. See the "1 bit binary decode format" in the
Raw Parameters window, and the
"bit reverse" operation and
"bit Raster" transform in the
Channel Mapping window.
NTP
Network Time Protocol. Used for accurate clock synchronization over the
Internet. See "man ntpq" and the
calibratesr command line option.
Nyquist
Nyquist sampling theorem.
For real signals; half the sampling rate is known as the Nyquist frequency
limit. This is the highest frequency that can be represented by a
particular sampling rate. Complex quadrature
signals have twice the bandwidth for a given sample rate. For baseband
complex signals the frequency range is { Hz, 0, +Hz } where Hz is half the
sample rate. For nonbaseband signals the frequency range is twice that
of a real signal.
OFDM
Orthogonal Frequency Division Multiplexing. A multicarrier data
modulation scheme that spreads multiple QAMlike channels
over FDM. Each channel has its own dynamically
adjustable modulation parameters that maximizes the total signal bandwidth and
reduces the effect of interference and multipath.
OSD
On Screen Display. Text overlays like a heads up display. Uses
minimal screen real estate in the display of important information. Most
baudline display windows use OSD for cursor and data specific metrics.
overlap
The amount to move the FFT sliding window for smooth and
continuous spectral slice processing. The overlap controls spectrogram
scrolling speed, time axis resolution, and FPS.
See the overlap slider in the
Scroll Control window.
PCM
Pulse Code Modulation. It defines the analog and digital signal
mapping (see ADC and DAC).
An analog signal is quantized into discrete digital samples at a uniform
sample rate. See Nyquist sampling theorem.
PDF
Probability Density Function.
The probability distribution of sample amplitudes.
See the Histogram window.
PLL
Phase locked loop. A feedback loop that consists of a phase detector,
LPF, and VCO. The PLL is a phase
tracking circuit whose output is a clock signal that is phase locked to the
input. Some useful applications: clock synchronization, frequency
multiplier, and FM discriminator.
PM
Phase Modulation.
PPM
Parts per million. Used as error units. See the
calibratesr command line option.
PPS
Pulse per second. Used for timing synchronization.
See GPS.
PSD
Power Spectral Density. A method of scaling the spectra amplitude axis
such that it becomes a continuous function of frequency. See the
psd command line option.
PSK
Phase Shift Keying. A data modulation scheme that involves changing the
phase of a carrier frequency.
See BPSK and QPSK.
8PSK uses 8 distinct phases for 3 bits per symbol.
See also FSK and QAM.
QAM
Quadrature Amplitude Modulation. A data modulation scheme that
is a combination of PSK with ASK.
256QAM has 8 bits per symbol. QAM has better data throughput and
better spectral efficiency than PSK but it requires a higher
SNR to achieve an equivalent BER.
QoS
Quality of Service. A general measure of signal quality and service
availability. Frequency bandwidth, phase jitter, latency (delay),
BER, SINAD, SNR, and
THD are common signal quality performance metrics.
Service availability is typically measured in units of the NINES where each
9 digit represents another order of magnitude of reliability. 7 nines
= 99.99999% = 3 seconds of downtime per year.
QPSK
Quadrature Phase Shift Keying. A data modulation scheme that involves
changing the phase of a carrier frequency. QPSK use 4 distinct phases
(0°, 90°, 180°, 270°) for 2 bits per symbol.
See PSK.
quadrature
Complex I/Q sampling. Two channels; inphase (I) and quadrature (Q)
create a complex signal with twice the standard Nyquist
bandwidth.
See the quadrature command line option.
RF
Radio Frequency spectrum. See these different RF bands:
 ULF (DC  30 Hz)
 ELF (30  300 Hz)
 VGC (300  3400 Hz)
 VLF (3  30 kHz)
 VHF (30  300 MHz)
 UHF (300  3000 MHz)
RFI
Radio Frequency Interference. A source of signal noise.
RGB
Red Green Blue. Color space. 888 RGB is 24 bpp
which represents 8bits for each of the red, green, and blue components.
565 RGB is 16 bpp. See CMY.
RMS
Root Mean Square. The square root of the mean of the squares.
sqrt(sum(x[i]^2)/n);
RPM
Revolutions per minute. A measure of rotation.
See the RPM measurement window.
SDR
Software Defined Radio.
SFDR
Spurious Free Dynamic Range.
A measure of dynamic range which is the ratio of the input signal to the
strongest non signal element (spurious peak).
See the SFDR measurement window.
SINAD
Signal to Noise and Distortion Ratio. Also known as THD+N.
A measure of signal purity.
See the SINAD measurement window.
SNR
Signal to Noise Ratio.
Useful for measuring the characterization of the noise floor.
See the SNR measurement window.
spectrogram
The spectrogram display is a flat three dimensional plot that is composed of
spectrum slices. The axis are time vs. frequency vs. color (spectral
energy). See the Spectrogram
window.
SPL
Sound Pressure Level. Intensity of sound measured in
dB. The 0 dB SPL reference point is 0.0002 ubar
(20 uPa) which is sometimes called the Threshold of Hearing. SPL meters
typically measure in dBA and dBC where (A) and (C) are frequency
weightings. See the different weighting curves in the
Equalization window.
SSB
Single SideBand. FDM with one of the two
sidebands suppressed making either upper (USB) or lower
(LSB) sideband. Sometimes the carrier is also
suppressed. The benefit of SSB over DSB is
better spectral efficiency and reduced power.
stderr
Standard Error. A streaming UNIX pipe mechanism. The output from
the debugrate and the
debugmeasure command line options
can be redirected with the shell ">&" and the "&" operators.
stdin
Standard Input. A streaming UNIX pipe mechanism. See the
stdin command line option to use baudline
as a data sink.
stdout
Standard Output. A streaming UNIX pipe mechanism. See the
stdout command line option to use baudline
as a data source.
T&M
Test and Measurement. See DUT.
TDM
Time Division Multiplexing. Interleave channels in time.
Examples: sound card PCM data, Compact Discs (CD's), and
voice carrying T1's.
TDMA
Time Division Multiple Access.
THD
Total Harmonic Distortion. A measure of nonlinearity.
Units can be dB or percent (%).
See the THD measurement window.
ulaw
An audio codec companding format more correctly known as mulaw. A
logarithmic mapping between 8 bit data space and 14 bit sample space as
described in the CCITT G.711 recommendation. ulaw has 14 bits of
dynamic range (84 dB). See Alaw.
USB
Dual definitions: Universal Serial Bus and Upper SideBand
(see SSB).
UHF
Ultra High Frequency. 300  3000 MHz.
ULF
Ultra Low Frequency. DC  30 Hz.
UTC
Coordinated Universal Time. Also known as Greenwich Mean Time
(GMT). Global scientific observations use UTC for time
synchronization. From a UNIX shell try the command "date u" for your
computer's time displayed relative to UTC. See the
utc command line option.
VBR
Variable Bit Rate.
More efficient than CBR but more difficult to implement in
realtime streaming applications since the data bandwidth is dynamic.
VCO
Voltage Controlled Oscillator.
VGC
Voice Grade Channel. It can refer to an analog channel with a frequency
range of 300 to 3400 Hz. Or it can refer to a digital 64 Kbps
PCM DS0 communications channel.
VHF
Very High Frequency. 30  300 MHz.
VLF
Very Low Frequency. 3  30 kHz.
WGN
White Gaussian Noise. See AWGN.
XOR
bitwise eXclusive OR. A = B ^ C; A reversible operation. See
the "XOR" operation
in the Channel Mapping window.
xruns
Overruns. Underruns. An error case that happens when either the
input sample buffers are full or the output sample buffers are empty. An
xrun results in a loss of data or an audible click. This error is usually
caused when the data bandwidth requirements exceed the CPU power. See
"potential drops" in the Stats window.




