## Numerix - DSP Glossary |

Adaptive Differential Pulse Coded Modulation (ADPCM) | A speech compression algorithm that adaptively filters the difference between two successive PCM samples. This technique typically gives a data rate of about 32 Kbps. |

Adaptive equalisation | A filtering system that can allow for the effects of a changing communications medium to be cancelled. |

Adaptive filter | A filter that can adapt its coefficients to model a system. |

Adaptive predictive coding | An LPC based speech compression technique that uses an adaptive predictive voice source. |

Aliasing | The effect on a signal when it has been sampled at less than twice its highest frequency. |

Amplitude Modulation | A communications scheme that modifies the amplitude of a carrier signal according to the amplitude of the modulating signal. |

Anti-aliasing filter | An analog filter that is used prior to sampling to limit the signal bandwidth to less than half the sample rate (generally low pass) to prevent aliasing distortion. |

Asynchronous communications | A communications system where the transmitter and receiver run independently. The beginning and end of the data packet are usually indicated by start and stop bits in the data stream. |

Attenuation | Decrease in magnitude. |

Autocorrelation | The correlation of a signal with a delayed version of itself. |

Band-pass filter | A filter that only allows a single range of frequencies to pass through. |

Band-stop filter | A filter that removes a single range of frequencies. |

Bandwidth | The range of frequencies that make up a more complex signal. |

Barrel shifter | Part of the ALU that allows single cycle shifting and rotating of data words. |

Baseband | Signals that have a frequency spectrum based around 0 Hz. E.G. speech. |

Baud rate | The rate at which symbols are transmitted over a communications channel. A symbol may contain one or more bits of information. |

Bit rate | The rate at which bits are transmitted and equals the baud rate * the number of bits per baud. |

Biquad | Typical 'building block' of IIR filters - from the bi-quadratic equation. |

Butterfly | The smallest constituent part of an FFT, it represents a cross multiplication, incorporating multiplication, sum and difference operations. The name is derived from the shape of the signal flow diagram. |

Companding | A logarithmic scheme for sampling analog signals that increases the resolution of signals with a low amplitude. Common standards include A-Law and u-Law. |

Convolution | An identical operation to Finite Impulse Response filtering. |

Correlation | The comparison of two signals in time, to extract a measure of their similarity. |

Data flow architecture | A multi-processing architecture where individual processing elements perform multiple instructions on a many pieces of data. |

Discrete Fourier Transform (DFT) | A transform that gives the frequency domain representation of a time domain sequence. |

Discrete sample | A single sample of a continuously variable signal that is taken at a fixed point in time. |

Echo canceller | A filter that will remove reflected signals on a transmission line that are caused by impedance mismatches. |

Equalisation | A filter that will compensate for the effects of a communications channel. |

Fast Fourier Transform (FFT) | An optimised version of the DFT. |

Finite Impulse Response (FIR) Filter | A filter that includes no feedback and is unconditionally stable. |

Floating-point | A number scheme that codes a value with a fraction and an exponent and allows a high signal dynamic range. |

Frequency Division Multiplexing (FDM) | A communications system that divides a single channel into smaller ones with discrete frequency bands. |

Frequency domain | The representation of the amplitude of a signal with respect to frequency. |

Frequency Shift Keying (FSK) | A digital modulation scheme that uses a different frequency to represent different binary levels. |

Full duplex | Communications in two directions simultaneously. |

Gain | Amplification or increase in magnitude. |

Half duplex | Communications in two directions, but only one at a time. |

Harvard Architecture | A microprocessor architecture that uses separate busses for program and data, this is typically used on DSPs to optimise the data throughput. |

High pass filter | A filter that allows high frequencies to pass through. |

Hybrid | An analog 2 wire to 4 wire (and vice versa) converter. |

Infinite Impulse Response (IIR) filter | A filter that incorporates data feedback. Also called a recursive filter. |

Linearity | A measure of the performance of an ADC or DAC to convert signals with different amplitudes, to the same degree of accuracy. |

Linear Predictive Coding (LPC) | A speech compression technique that is based on modelling the vocal tract with a time varying filter. |

Low pass filter | A filter that allows low frequencies to pass through. |

Multi-processing | The division of a process across several processors to improve the performance of the system. |

Multi-tasking | The division of processor across several tasks, such that each one is able to receive its required number of processor cycles. |

Multiple Instruction Multiple Data (MIMD) | See data flow architecture. |

Modulation | The modification of the characteristics of a signal so that it might carry the information contained in another signal. |

Parallel processing | The execution of tasks in parallel, either on a single processor via multi-tasking or across several processors by multi-processing. |

Pass band | The frequency range of a filter through which a signal may pass with little or no attenuation. |

Phase Shift Keying (PSK) | A digital modulation scheme that uses a constant frequency carrier with a variable phase. |

Pipelining | A technique commonly used in high performance microprocessors that allows an instruction to begin execution before previous ones have been completed. |

Pole | Artefact leading to frequency dependent gain in a signal. Generated by a feedback element in a filter. |

Pulse Code Modulation (PCM) | The effect of sampling an analog signal. |

Quadrature Amplitude Modulation (QAM) | A variation of PSK that incorporates AM to increase the number of bits per baud. |

Recursive filter | See Infinite Impulse Response filter. |

Resolution | The accuracy of and ADC or DAC circuit. |

Sampling | The conversion of a continuous time analog signal into a discrete time signal. |

Sample rate | The inverse of the time between successive samples of an analog signal. |

Single Instruction Multiple Data (SIMD) | A multi-processing architecture where individual processing elements perform the same instruction on many pieces of data, also referred to as a systolic array. |

Spectrum analyser | An instrument that displays the frequency domain representation of a signal. |

Stop band | The frequency range of a filter through which a signal may NOT pass and where it experiences large attenuation. |

Synchronous communications | A communications system where the data is transmitted and received at discrete times, which are usually synchronized by a clock signal. |

Systolic array | See Single Instruction Multiple Data. |

Time domain | The representation of the amplitude of a signal with respect to time. |

Transducer | A piece of equipment that converts a physical signal into an electrical signal. |

Twiddle factor | The coefficients of the FFT algorithm, typically a ¾ sine table. |

Von-Neumann architecture | A traditional microprocessor architecture that uses the same bus for program and data. |

z-domain | The discrete frequency domain, in which the jw axis on the continuous time s-plane is mapped to a unit circle in the z-domain. |

Zero | Artefact leading to frequency dependent attenuation in a signal. Generated by a feedforward element in a filter. |

Return To Home Page | SigLib DSP Library | DFPlus™ Filter Designer | DSP Abbreviations

If you have
any comments or questions please email Numerix : numerix@numerix-dsp.com

Copyright © 2008, Indigo Consulting Ltd..
Permission is granted to create WWW pointers to this document.
All other rights reserved. All trademarks acknowledged.