- #1
rude man said:Well, acctually, you're looking at it:
H(f) = 0, f < f1
H(f) = 1, f1 < f < f2
H(f) = 0, f > f1
where f2 - f1 = BW.
This filter BTW is unrealizable since its input-output relationship is not causal ...
From a web page:
<< Impulse Response and Causality
• All the impulse responses of ideal filters are
sinc functions, or related functions, which
are infinite in extent
• Therefore all ideal filter impulse responses
begin before time, t = 0
• This makes ideal filters non-causal
• Ideal filters cannot be physically realized,
but they can be closely approximated >>
Davidlong said:I have the following equation for finding the impulse response function. The equation is the inverse Fourier transform of the H(f) equation.(infinity and -infinity are the limits) h(τ)=∫e(2∏jfτ)H(f)df.
I replaced the limits with f2 and f1 which represent F+BW/2 and F-BW/2 respectively.
For the integral i get [H(f)/2∏jf]*[e(2∏jfF2)-e(2∏jfF1)].
I don't understand what value i should use for H(f), should it just be 1? And would that be the full expression for the impulse response or can it be simplified further?
Thanks
This is incorrect. It is a single sinc function, which the OP can determine by factoring the exponential terms and applying a trig identity as I suggested.rude man said:The impulse reponse to an ideal bandpass filter is the sum of two sinc functions, one for each corner frequency, as you may be able to determine by taking the inverse Fourier of H(f).
To be precise, the theoretical impulse response has finite amplitude, but extends in time from -∞ to ∞.rude man said:The impulse response has infinite delay and the output can build up to infinity, so it's not of much use except for theoretical work.
marcusl said:This is incorrect. It is a single sinc function, which the OP can determine by factoring the exponential terms and applying a trig identity as I suggested.
To be precise, the theoretical impulse response has finite amplitude, but extends in time from -∞ to ∞.
Davidlong said:Yes it's a low pass filter. Do I use eulers formula to factor the exponentials and then apply the trig function?
For the frequency response the equation ends in dt, so its a function of t. For impulse response it ends in df so the impulse response is a function of f. Am i correct on this?
Davidlong said:So if there's 2 sinc functions do i have 2 different integrals? So for example with limits Fc to fc-BW/2 and fc+BW/2 to Fc?
For a low pass filter the sinc function is 2.Fc.sinc(2.Fc.t) when the limits are Fc and -Fc. But I'm not sure how to achieve this if it's a band-pass filter.
An LTI (Linear Time-Invariant) system is a type of system in which the output signal is a linear combination of the input signal, with the same time shift regardless of the input signal. In simpler terms, it means that the system's response to an input signal is always the same, regardless of when the input signal is applied.
The frequency response of an LTI system is a mathematical representation of how the system responds to different frequencies in the input signal. It is usually expressed as a function of frequency and can be represented graphically as a plot of magnitude and phase response.
The frequency response of an LTI system can be calculated using the transfer function of the system, which is the ratio of the output signal to the input signal in the frequency domain. The transfer function can be obtained by applying the Laplace transform to the system's differential equations.
The magnitude response of an LTI system represents the system's gain at different frequencies. It shows how the system amplifies or attenuates different frequencies in the input signal. It is usually expressed in decibels (dB) and can be used to determine the system's frequency selectivity.
The phase response of an LTI system represents the phase shift of the output signal compared to the input signal at different frequencies. It is an important parameter in signal processing as it can affect the overall signal quality. It is usually expressed in degrees or radians and can be used to determine the system's frequency delay.