唐斌-数字信号处理课件-chp5 第1讲.pptVIP

Ch5. Transform Analysis of Linear Time-Invariant Systems Main contents The frequency response of LTI systems 5.0 Introduction How to represent a LTI system? 5.1 The frequency response of LTI systems 5.1.1 Ideal frequency-selective filters 5.1.1 Ideal frequency-selective filters 5.1.1 Ideal frequency-selective filters 5.1.2 Phase distortion and delay 5.1.2 Phase distortion and delay Example 5.1 Effects of Attenuation and Group Delay Frequency response for rational system functions System functions for system characterized by linear constant-coefficient difference equations All-pass systems Linear systems with generalized linear phase Minimum-phase systems Relationship between magnitude and phase In time-domain: impulse response: h[n] In frequency-domain: frequency response: In z transform domain: system function: Expressed in polar form: magnitude response or gain phase response or phase shift If the magnitude and phase effects are undesirable, — magnitude distortion — phase distortion lowpass: highpass: IFT IFT bandpass: bandstop: IFT IFT Properties: noncausal, IIR, not computationally realizable zero-phase Ideal delay system: Ideal lowpass filter with linear phase: Linear phase FT Delay distortion is a rather mild form of phase distortion; often it is inconsequential, or it could easily be compensated. —— A convenient measure of the linearity of the phase definition: The deviation of the group delay from a constant indicates the degree of nonlinearity of the phase. Group delay (群延迟) continuous phase: e.g. 0.85 0.25 0.5 0.25 0.5 0.85 delay 200 samples delay 50 samples