Signal Processing Topics

ACK
In telecommunications, this is the acknowledge character in many data codes; used most commonly for an affirmative response of correct receipt.
Alias
A false lower frequency component that appears in sampled data acquired at too low a sampling rate.
Amplitude Flatness
A measure of how close to constant the gain of a circuit remains over a range of frequencies.
Angular Rate Sensor
A sensor that measures rotational velocity around its sensitive axis.
Anti-Aliasing Filter
A device that attenuates signal content outside the desired bandwidth.
Asymmetric Waveform
A waveform that has unequal excursions above and below the horizontal axis.
Autocorrelation
The autocorrelation function gives a measure of the extent to which a signal correlates with a displaced version of itself, as a function of the displacement.
Autocovariance
This is the degree to which a function is correlated with itself as a function of time.
Autospectrum
A spectrum with the coefficients of the components expressed as the square of the magnitudes
Band Stop Filter
An electronic network which passes signals having frequencies above and below the band-elimination frequency span.
Bandpass Filter
An electronic network which transfers through it a specific band of signal frequencies.
Bandwidth
The bandwidth of a filter is the separation between the lower and upper frequencies at which the amplitude of a sinusoidal signal is attenuated by a factor of 2.
Bandwidth Time Product
Used in calculating the confidence limit of a measurement.
Base Band
The frequency band occupied by information-bearing signals before combining with a carrier in the modulation process.
Bins
The individual frequencies at which the amplitudes are calculated, commonly called lines.
Bit Error Rate
The number of bits processed before an erroneous bit is found.
Bit Rate
The rate or frequency at which bits appear in a bit stream.
Bit Stream
A binary signal without regard to grouping.
Blackman Window
A weighting that is applied in the time domain to reduce leakage within a Fourier Transform analysis.
Blackman-Harris Window
A weighting that is applied in the time domain to reduce leakage within a Fourier Transform analysis. The Blackman-Harris window has much the same performance as the Kaiser-Bessel window, except that it suppreses the sidelobes more than 92dB at a cost of an 11% wider noise bandwidth.
Bohman Window
A weighting that is applied in the time domain to reduce leakage within a Fourier Transform analysis.
Calculated Peak
Term used to describe the spectral overall RMS level multiplied by the square root of two.
Campbell Diagram
A mathematically constructed diagram used to check for coincidence of vibration sources with natural resonances.
Cauchy Window
A weighting that is applied in the time domain to reduce leakage within a Fourier Transform analysis.
Cepstrum
A cepstrum is a time history defined as the power spectrum of the logarithm of the Power spectrum.
Chirp
A chirp is a sound that has a rapid increase in frequency.
Circular Frequency
The frequency of a steady recurring phenomenum in radians per second.
Clipper Circuit
A circuit that blocks or removes the portion of a voltage waveform above some threshold voltage.
Coherence
This gives a measure of the linear dependence between signal A and B.
Colourmap
This is a method of plotting noise or vibration versus engine speed and frequency simultaneously.
Comb Filter
A distortion produced by combining an electrical or acoustical signal with a delayed replica of itself.
Common-Mode Range
The input range over which a circuit can handle a common-mode signal.
Composite Rating of Preference
Combines low frequency sound and spectral balance i.e. modifiers for boom and high frequency.
Constant Percentage Bandwidth Filter
A band-pass filter whose bandwidth is a constant percentage of centre frequency. 1/3 octave filters are constant percentage bandwidth.
Control System
A group of components systematically organized to perform a specific control purpose.
Convolution
Convolution meaning ..intertwined, coiled…
Correlation
Generally speaking, a similarity between data; the extent to which data are related.
Covariance
A measure of the joint variability of a pair of numeric variables.
Crest Factor
Peak value divided by the R.M.S. value, used as a measure of the severity of a segment of data.
Cross Correlation
The cross-correlation function gives a measure of the extent to which two signals correlate with each other as a function of the time displacement between them.
Cross Modulation
The modulating of a desired signal carrier by undesired signal modulation as the result of accidental mixing of the two signals in a non-linear device.
Cross Spectrum
The cross spectrum Fxy(f) of fx(t) and fy(t) is the forward Fourier Transform of the cross correlation function Rxy(T). The cross spectrum is in general complex.
Cyclic Redundancy Check
An integrity checking process for block data.
DAC
Abbreviation of Digital-to-Analogue Converter.
DAQ
Abbreviation of Data Acquisition.
Data Acquisition
Collecting and measuring electrical signals from sensors, transducers, and test probes or fixtures and inputting them to a computer for processing.
Data Processing
The execution of a systematic sequence of operations performed upon data. Synonymous with information processing.
Date Stamp
Information added to data to indicate the date at which it was collected.
DC Component
The dc value of an waveform that has a value other than zero.
Definition of a Sound
This may be described by the time at which the sound arrives at the listening position.
Degenerative Feedback
Feedback in which the feedback signal is out of phase with the input signal.
Delta-Sigma Modulating ADC
A high-accuracy circuit that samples at a higher rate and lower resolution than is needed and pushes the quantization noise above the frequency range of interest.
Differentiation
A mathematical operation that differentiates a signal or function.
Digital Audio Compression
Any of several algorithms designed to reduce the number of bits required for accurate digital audio storage and transmission.
Digital Filter
Any filter accomplished in the digital domain.
Digital Signal Processing
The term used for calculations performed on digital signals.
Digital-to-Analogue Converter
Converts a digital number into a corresponding analogue voltage or current.
Digitization
Any conversion of analog information into a digital form.
Direct Sequence Modulation
A spread spectrum modulation scheme that directly modulates the information-bearing data with a spreading code sequence.
Discrete Fourier Transform
The digital version of the fourier transform.
Discrete Gabor Transform
An algorithm for transforming data from the discrete time domain to the joint time-frequency domain.
Dropout
Any discrete variation in signal level during the reproduction of recorded data which results in a data-reduction error.
Effective Number of Bits
Figure of merit for an A/D converter describing how many bits of effective resolution, this is below the actual A/D word size.
Electronic Filter
Any of various electric, electronic, acoustic, or optical devices used to reject signals, vibrations, or radiation of certain frequencies while passing others.
Equivalent Rectangular Bandwidth
This is the effective bandwidth of an auditory filter.
External Trigger
A voltage pulse from an external source that triggers an event such as A/D conversion.
Far-End Crosstalk
A common telephony impairment created by physical twisted wire pairs sharing a bundle.
Fast Fourier Transform
An algorithm, or digital calculation routine, that efficiently calculates the discrete Fourier transform from the sampled time waveform.
Filter
Any of various electric, electronic, acoustic, or optical devices used to reject signals, vibrations, or radiation of certain frequencies while passing others.
Filtering
Attenuates components of a signal that are undesired: reduces noise errors in a signal.
Finite Impulse Response Filter
A commonly used type of digital filter. Digitized samples of the audio signal serve as inputs, and each filtered output is computed from a weighted sum of a finite number of previous inputs.
FIR Filter
A commonly used type of digital filter. Digitized samples of the audio signal serve as inputs, and each filtered output is computed from a weighted sum of a finite number of previous inputs.
Flattop Window
An amplitude weighting of the time signal used with gated continuous signals to give them a slow onset and cut-off in order to reduce the generation of side lobes in their frequency spectrum.
Flicker Noise
A type of low frequency noise where the power spectral density is inversely proportional to the frequency.
Fluctuation Strength
This is similar in principle to roughness except it quantifies subjective perception of slower, up to 20Hz, amplitude modulation of a sound.
Fourier Analysis
A mathematical analysis of waves, discovered by the French mathematician Fourier (1768-1830).
Fourier Series
Decomposes periodic functions or periodic signals into the sum of a set of simple oscillating functions.
Fourier Transform
The mathematically rigorous operation which transforms from the time domain to the frequency domain and vice versa.
Frequency Shift
A sudden change in the frequency of a signal.
Gaussian Noise
Another name for Random Noise.
G Weighted Overall Level
This purportedly reflects human response to infrasound.
Hamming Window
An amplitude weighting of the time signal used with gated continuous signals to give them a slow onset and cut-off in order to reduce the generation of side lobes in their frequency spectrum.
Hanning Window
An amplitude weighting of the time signal used with gated continuous signals to give them a slow onset and cut-off in order to reduce the generation of side lobes in their frequency spectrum.
Hanning-Poisson Window
A weighting that is applied in the time domain to reduce leakage within a Fourier Transform analysis.
Harmonic Analysis
Statistical method for determining the amplitude and period of certain harmonic or wave components in a set of data with the aid of Fourier series.
High Pass Filter
A filter that passes signal frequencies above a specific, or cut off, frequency is called a high pass filter.
Image Frequency
An undesired frequency capable of producing the desired frequency through heterodyning.
Infinite Impulse Response Filter
A commonly used type of digital filter. This recursive structure accepts as inputs digitized samples of the audio signal, and then each output point is computed on the basis of a weighted sum of past output (feedback) terms, as well as past input values.
Instantaneous Amplitude
The amplitude at any given point along a wave at a specific instant in time.
Instantaneous Value
The magnitude at any particular instant when a value is continually varying with respect to time.
Integrating ADC
An ADC whose output code represents the average value of the input voltage over a given time interval.
Interaural Cross-Correlation Coefficient
The measure of the difference in the sounds arriving at the two ears of a listener.
Intermodulation
The mixing of two or more signals in a nonlinear element to produce signals at new frequencies which are sums and differences of the input signals or their harmonics.
Intermodulation Distortion
Distortion produced by the interaction of two or more signals. The distortion components are not harmonically related to the original signals.
Jitter
The short-term instability of a signal.
Joint Time Frequency Analysis
A method of analysis that simultaneously provides both time and frequency information.
JTFA
Abbreviation of Joint Time Frequency Analysis.
Kaiser Bessel Window
A weighting that is applied in the time domain to reduce leakage within a Fourier Transform analysis.
Kalman Filter
A technique for estimating an unknown state of a linear dynamic system given observations of the system which have additive (Gaussian) noise.
Lead Term
A control system component that anticipates future inputs based on the current signal trend.
Leakage
In a Fourier Transform the signal is assumed to be periodic. If a pure sine wave does not repeat exactly within the time window, it is truncated. this truncation will lead to the frequency domain resultant being smeared (leakage) and not a single frequency.
Linear Distortion
Magnitude and phase distortion.
Low Pass Filter
A filter with a characteristic that allows all frequencies below a specified rolloff frequency to pass and attenuate all frequencies above.
Lower Frequency Cutoff
The lowest frequency a circuit will pass.
Lower Sideband
All difference frequencies below that of the carrier.
Mains Frequency
Electricity ac supply frequency; 50 Hz in UK, 60 Hz in US.
Mark
An interval during which a signal is present.
Maximum Length Sequence
A type of pseudorandom binary sequence.
Minimum Discernible Signal
The weakest input signal that produces a usable signal at the output of a receiver.
Modulated Wave
A complex wave consisting of a carrier and a modulating wave.
Modulation
The process, or the result of the process, by which a characteristic of one wave is varied according to some characteristic of another wave.
Moving Picture Experts Group
A working group within SMPTE who set, among other things, specifications for compression schemes for audio and video transmission.
Multiplexing
A method for simultaneous transmission of two or more signals over a common carrier wave.
Near-End Crosstalk
Impairment typically associated with twisted-pair transmission, where a local transmitter interferes with a local receiver.
Noise Climate
This is sometimes calculated as LA10 - LA90 and represents the fluctuations in noise.
Nonlinear Distortion
New spectral components are produced.
Notch Filter
An electronic network which passes signals having frequencies above and below the band-elimination frequency span.
Order Analysis
Order analysis is simply frequency analysis where the frequency axis of the spectrum is expressed in orders of rpm rather than in Hz or rpm.
Overall RMS Level
A measure of the total RMS magnitude within a specified frequency range.
Overdriven
When the input signal amplitude is increased to the point that the transistor goes into saturation and cutoff.
Overlap Processing
Overlap processing is desirable when using a Hanning Window because it ensures against loss of data for parts of the signal that occur near the beginning and end of the window.
Overmodulation
A condition that exists when the peaks of the modulating signal are limited.
Oversampling
Sampling at a rate higher than the sampling Nyquist theorem.
PAM
Abbreviation of Pulse Amplitude Modulation
PDM
Abbreviation of Pulse Duration Modulation.
Peak to Average Power ratio
Usually expressed in decibels and used to determine the robustness of a modulated signal against nonlinear distortion.
Percent of Modulation
The degree of modulation defined in terms of the maximum permissible amount of modulation.
Periodic Wave
A waveform that undergoes a pattern of changes, returns to its original pattern, and then repeats the same pattern of changes.
PFM
Abbreviation of Pulse Frequency Modulation.
Phase Angle
The number of electrical degrees of lead or lag between the voltage and current waveforms in an ac circuit.
Phase Delay
The time or angular difference between two signals.
Phase Modulation
Angle modulation in which the phase of the carrier is controlled by the modulating waveform.
Phase Shift
The time or angular difference between two signals.
Picket Fence Effect
The true spectrum of the signal being analyzed may have peaks at frequencies between the lines of the FFT spectrum, and the peaks in the FFT spectrum will not be at exactly the correct frequencies.
Positive Alternation
The part of a sine wave that is above the reference line.
Positive Feedback
Feedback in which the feedback signal is in phase with the input signal.
Post Triggering
The technique used on a DAQ board to acquire a programmed number of samples after trigger conditions are met.
Power Standing Wave Ratio
The ratio of the square of the maximum and minimum values of a wave.
PPM
Abbreviation of Pulse Position Modulation.
Pre Triggering
The technique used on a DAQ board to keep a continuous buffer filled with data, so that when the trigger conditions are met, the sample includes the data leading up to the trigger condition.
PSWR
Abbreviation of Power Standing Wave Ratio.
PTM
Abbreviation of Pulse Time Modulation.
Pulse
Signal characterized by a steep rise from and decay toward an initial level.
Pulse Amplitude Modulation
Pulse modulation in which the amplitude of the pulses is varied by the modulating signal.
Pulse Compression
Any technique for modifying or processing a pulse so that the autocorrelation function is greater than one.
Pulse Duration
The period of time during which a pulse is present.
Pulse Duration Modulation
Pulse modulation in which the time duration of the pulses is changed by the modulating signal.
Pulse Frequency Modulation
Pulse modulation in which the modulating voltage varies the repetition rate of a pulse train.
Pulse Modulated Field
An electromagnetic field produced by the amplitude modulation of a continuous wave carrier by one or more pulses.
Pulse Modulation
A form of modulation in which one of the characteristics of a pulse train is varied.
Pulse Oscillator
A sine-wave oscillator that is turned on and off at specific times.
Pulse Output Power
The ratio of the average output power to the pulse duty factor.
Pulse Position Modulation
Pulse modulation in which the position of the pulses is varied by the modulating voltage.
Pulse Repitition Rate
The average number of pulses in unit time during a specified period.
Pulse Time Modulation
Pulse modulation that varies one of the time characteristics of a pulse train.
Pulse Width
Duration of time between the leading and trailing edges of a pulse.
Pulse Width Modulation
Pulse modulation in which the duration of the pulses is varied by the modulating voltage.
PWM
Abbreviation of Pulse Width Modulation.
Quadrature Amplitude Modulation
A combined phase- and amplitude-modulation scheme that is used to modulate the carrier signal in phase quadrature.
Quadrature Phase-Shift Keying
A digital phase-modulation scheme that is used to modulate the carrier signal in phase quadrature.
Quantization Error
When a continuous time signal is digitized, because there isn′t an infinite number of discrete digital levels, the difference between the actual analog value and the digital representation of that value is defined as the quantization error.
Quasi Periodic
A deterministic signal whose spectrum is not a harmonic series, but nevertheless exists at discrete frequencies.
Real Time Monitoring
Observing measured results as they are happening.
Real Time Operation
What is perceived to be instantaneous to a user. This is particularly applicable to Hardware in Loop systems where any simulation of a system must operate in real time to allow inputs and outputs to operate as per real time.
Rectangular Window
An amplitude weighting used to truncate continuous time signals to fit within the length of the DFT window.
Recursive Filter
A filter in which there is no need to store past measurements for the purpose of calculating current estimates.
Rest Frequency
The carrier frequency during the constant-amplitude portions of a phase modulation signal.
Ringing Oscillator
A sine-wave oscillator that is turned on and off at specific times.
Ripple Frequency
The frequency of the ripple current.
Root Mean Square
This is the square root of sum of squares of individual observations divided by the total number of observations made.
Sample and Hold
A circuit that captures and holds an analog signal for a finite period.
Sample Rate Conversion
The process of converting one sample rate to another.
Sampling
The process of representing the amplitude of a signal at a particular point in time.
Sampling Theorem
States that a band limited continuous waveform may be represented by a series of discrete samples if the sampling frequency is at least twice the highest frequency contained in the waveform.
Selectivity
The ability of a receiver to select the desired signal and reject unwanted signals.
Shaping Circuit
A circuit that alters the shapes of input waveforms.
Signal Ground
The common return or reference point for analog signals.
Sine Wave
A waveform corresponding to a single-frequency periodic oscillation that can be mathematically represented as a function of amplitude versus angle in which the value of the curve at any point is equal to the sine of that angle.
Spatial Filtering
Enhancing an image by increasing or decreasing its spatial frequencies.
Spectral Centroid
This is the centre of gravity of a frequency spectrum.
Spectrum
A spectrum is a definition of the magnitude of the frequency components that constitute a quantity.
Spectrum Analyser
An instrument for measuring, and usually recording, the spectrum of a signal.
Spectrum Density
Limit, as the bandwidth approaches zero, of the mean-square amplitude divided by bandwidth.
Speech Intelligibility
A measure of sound clarity that indicates the ease of understanding speech.
Splatter
Unwanted sideband frequencies that are generated from over modulation.
Spread Spectrum Modulation
Digital modulation scheme that spreads the system bandwidth far greater than the minimum required bandwidth.
Square Wave
A periodic wave that alternately assumes one of two fixed values (high and low) with the transition time between these two levels being negligible.
Stage Support
Early energy (20 to 100ms), sound source on the stage 1m away from the microphone.
Standing Wave Ratio
The ratio of the maximum to the minimum points of a wave.
Step by Step Counter
A counter that provides an output for each cycle of the input in one-step increments.
SWR
Abbreviation of Standing Wave Ratio.
Time Delay Spectrometry
A method for obtaining anechoic results in echoic spaces.
Time History
A continuous record of the variation of a physical quantity (e.g. displacement, acceleration, force, etc.) with time.
Time Series
A sample of data values collected at equally spaced points in time.
Tracking Filter
A low-pass or band-pass filter which automatically tracks the input signal.
Trellis-Code Modulation
Combined coding and modulation technique.
Trigger
A short pulse, either positive or negative, that can be used to cause an electronic function to take place.
Turnover Frequency
Also known as Nyquist Frequency.
Uniform Window
The uniform, or rectangular, window does not modify the signal amplitude at all.
Unmodulated
A carrier signal without modulation.
Velocity Servosystem
A servosystem which controls the speed of the load it is driving.
Waterfall Plot
A series of spectral maps taken at regular intervals of time or at regularly spaced shaft speeds, similar to the flow of a waterfall.
Waveform Analysis
Observation displays of voltage and current variations with respect to time or by harmonic analysis of complex signals.
Wavelet
The wavelet allows a rapidly changing time history (e.g. door slam noise) to be investigated in the frequency domain.
Windowing
An amplitude weighting of the time signal used with gated continuous signals to give them a slow onset and cut-off in order to reduce the generation of side lobes in their frequency spectrum.
Z Transform
A mathematical method used to relate coefficients of a digital filter to its frequency response, and to evaluate stability of the filter.

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