# Shared Flashcard Set

## Details

Digital Signal Theory
Digital Filters
29
Computer Science
05/09/2012

Term
 Causal Filter
Definition
 The output depends on any current, past, or future input. (EQ, reverb, delay, etc.)
Term
 Non-Causal Filter
Definition
 The output is not dependent on any current, past, or future input (pre-delay)
Term
 Linear Time Invariant Filter (LTI)
Definition
 A digital filter where there is no harmonic distortion clipping, no intermodulation distortion, both linear and time invariant, is causal.
Term
 Reverb
Definition
 LTI filter, both linear and time-invariant.
Term
 EQ
Definition
 LTI filter
Term
 Compressor
Definition
 Time invariant filter.
Term
 Impulse
Definition
 A time domain signal that has as high of an amplitude as possible at 0, but has zero amplitude. Characterized by a loud, short sound. The shorter the signal, the wider the spectrum & vice versa.
Term
 Impulse Response
Definition
 The response to an impulse, that contains all frequencies in an response at equal amplitudes. Works in the time domain.
Term
 Convolution
Definition
 The sum of every sample of the input signal, multiplied by the sum of every sample of the impulse, added together, produces a convolved signal.-Convolved signals will be either scaled or delayed-The output of the convolved signal should be N+M-1, where the length of output signal is one sample shorter than the sum of the lengths of the two convolved signals put together.
Term
 The law of convolution
Definition
 Convolution in the time domain is equal to multiplication in the frequency domain.
Term
 Fast Convolution
Definition
 1) Two signals are convolved together in the time domain2) An FFT occurs to bring the two signals into the frequency domain3) They are multiplied together; essentially convolving them4) An IFFT occurs to bring the convolved signal back into the time domain.
Term
 Feed Forward Filter
Definition
 A simple delay, which is added together towards the output Z-^1*Multiplied by x[n]
Term
 Feedback Filter
Definition
 Coefficients are subtracted together from the output.*Multiplied by y[n]
Term
 Digital Filter Equation
Definition
 Noncausal, LTI, Direct Form IIy[n] = [the sum of all feed forward] coefficients] x[n-i] - [the sum of all feedback coefficients] y [n-j]
Term
 Finite Impulse Response Filter (FIR)
Definition
 A feedforward only filter.
Term
 Infinite Impulse Response Filter (IIR)
Definition
 A feeback filter, that is potentially unstable.
Term
 Filter Order
Definition
 1st order = y[n] = x[n] + x[n-1]2nd order = y[n] = 0.5x[n] - 0.5
Term
 Impulse Response Equation
Definition
 x = [1 0 0 0 0 0 0 0 0 0]
Term
Definition
 A stable input will produce a consistent output.
Term
 Unstable Filter Response
Definition
 an infinite impulse will produce and unstable, infinite response. IIR Filter.
Term
 Transient Time (Decay TIme)
Definition
 The T60 of an impulse for an IIR Filter. The filter order divided by the sample rate for a FIR Filter.
Term
 Bandwidth of a Filter
Definition
 The distance from peak to peak.
Term
 Center Frequency (fcenter, Q), Resonant Frequency
Definition
 One frequency is accentuated, while all others are sharply cutoff; determines the type of filter.
Term
 Measuring the bandwidth of a filter
Definition
 fcenter / bandwidthHigher bandwidth = the smaller the center frequency will be, producing a duller filter.Lower bandwidth = higher center frequency and a sharper filter.
Term
Definition
Term
 Comb filter
Definition
 All frequencies are cancelled out at evenly spaced frequencies.[1 0 0 0 0 0 0 0 0 0 0] = evenly spaced frequencies, close together [1 0 0 0] = widely spaced apart frequencies
Term
 IIR Comb Filter
Definition
 Sharp resonant peaks
Term
 Poles
Definition
 Feedback coefficients
Term
 Zeros
Definition
 Feedforward coefficents
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