Questions tagged [digital-filters]

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RRC filter has massive impulse response

I am trying to pass a BPSK signal through a root-raised cosine filter in Octave. To do this, I convolve the signal with the impulse response of an RRC filter, defined as follows (source): The BPSK ...
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1 vote
1 answer
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Power of noise signal through a matched filter (Digital Receiver)

I am studying matched filters and the sense of signal to noise ratio. In a question I was given, stated that: Show that a matched filter of a signal $s(t)$ maximizes the SNR of the output on a ...
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3 votes
2 answers
185 views

Is it ok to use MATLAB ''freqs" command for Digital filters?

According to my understanding, IIR filters are somewhat analog as they are based upon analog prototypes such as butterworth,chbeyshev etc. Can we usefreqscommand to ...
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1 answer
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Autocorrelation and the dot product of complex signals

I have a question for the signal processing community. When trying to calculate the autocorrelation of an array containing complex data, could the result be purely imaginary, and is there any ...
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2 answers
693 views

Poles and zeros form of a transfer function

I know that a transfer function for a discrete-time LTI system can be written in the form $$ H(z) = \frac{Y(z)}{X(z)} = \frac { \displaystyle\sum_{m=0}^M {b_m z^{-m}}} {1 + \displaystyle\sum_{n=1}^...
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one tap equalizer... what if there is none?

if I have a one tap equalizer system for OFDM, if I don't have an equalizer, what is received? is it just a load of noise?
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Windowed Sinc vs Parks–McClellan filter design [duplicate]

In the context of FIR filters, what are the tradeoffs between using a low pass filter designed using a windowed sinc versus an optimally iterative algorithm such as Parks-McClellan? When would you use ...
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5 votes
1 answer
628 views

Why don't unit circle poles lead to infinite amplitude response for Butterworth lowpass?

This is probably a very stupid question. In many places (e.g. here), the Butterworth filters, e.g. lowpass, are described as being "allpole" filters, that have all of these poles on the unit ...
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2 votes
1 answer
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Specify notch bandwidth by pole placement

I am trying to implement a notch filter by placing zeros and poles. I found in this thread how to specify the frequency to be filtered out (referred to as $\omega_n$ in previous link,) but it is not ...
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1 vote
1 answer
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Savitzky-Golay filtering (not smoothing) in real time

I would like to filter some data in an online sense i.e. $$y(t) = a0 + a1*y(t-1) + a2*y(t-2) + ... $$ the order not important. My understanding of the SG is that it is really a smoother - I have to ...
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2 answers
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Butterworth filter cutoff attenuation is not exactly 0.707(-3dB)

The documentation of scipy Butterworth filter says its cutoff attenuation is 0.707(-3dB). To validate this, I created a square wave signal, performed FFT and implemented a bandpass filter with a band ...
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Stability of N-order Thiran delay filter when required passband delay is N+1

In this lecture note, on page 7 (or page 111, the same page), it is said that the Thiran allpass delay filter of order N with passsband delay N+1 reproduces samples with zero error. I find it hard to ...
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7 votes
4 answers
426 views

Find the Transfer Function from Magnitude and Phase Response

We can use common algorithms such as what is available in firls and firpm in MATLAB for least squares or minimax fitting to ...
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1 vote
2 answers
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What is considered a Digital Filter

Would upscaling from a DVD to 4k on a TV be considered Digital Filtering? Would an AI trained to suppress noise and enhanced desired signal be considered a Digital Filter? I'm trying to figure out ...
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0 votes
1 answer
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What kind of filter is z / (z + 0.5)?

z / (z - e^-aT) is a low pass filter. z / (z - 1) is an integrator. What is z / (z + 0.5) ? In the time domain, it is Yn = Xn - 0.5Yn-1. It changes sign every iteration. Is this useful or should it ...
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1 answer
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A real-time (causal, non-symmetric) lowpass FIR filter with minimal passband ripple and phase

I am looking for a lowpass FIR filter that is causal (all samples used are current or past) and exhibits very low passband ripple and has passband phase very close to zero, which necessitates a filter ...
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0 votes
1 answer
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Formula to compute FIR and IIR Filter coefficients

I am trying to understand filter design. I am trying to implement butterworth filter which would have high,low and bandpass using the difference equation representation for FIR and IIR. Given the low ...
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pan-tompkins algorithm for qrs detection

1- in pan-tompkins algorithm a bandpass filter of cuttoff frequency of 5hz-11hz was used , can i use a bandpass filter of 0.5hz-45hz instead with the same algorithm ? 2-why do we need moving window ...
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Frequency filtering in the frequency domain vs. time domain

As a DSP newbie, I've stumbled into doing band pass filtering (of pre-recorded IQ data) in the frequency domain - which allows brick wall filtering (I'm just setting the IQ values of each consecutive ...
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1 answer
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Does FIR filter remove DC offset properly?

I was checking FIR and IIR filter for offset removal. But I found that FIR can not remove DC offset properly. I think there's something more to do with the filter coefficients of FIR to remove DC ...
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0 votes
2 answers
196 views

Why the output of an IIR filter is growing even though the filter is stable as per matlab and all its poles and zeros are within the ROC?

I have designed four IIR bandpass filters in MATLAB. The filters have their poles and zeros inside the ROC in Z-domain.I have checked that the filter is stable using the isstable function in matlab....
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Convolution between bit stream sampled by N number of samples per bit with a channel modeled as low pass filter

I generated a bit stream in MATLAB, from the transmitter to be convoluted by the channel I use MATLAB function "randi" between 0 & 1, so it generates random vectors of 0s & 1s and ...
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4 votes
3 answers
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Inverse DFT on the first half time domain

Assume to have c[] representing N DFT coefficients. The complex-valued signal of N samples in the time domain is computed by ...
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Adaptive Notch Filter python implementation

I am trying to implement an adaptive notch filter in Python to test various input signals disturbances. The itended use is for grid frequency and phase synchronisation, based on this research paper : ...
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10 votes
1 answer
863 views

What is the maximum output of an IIR filter?

I am implementing an IIR filter in an embedded device based on ARM. It is implemented as a cascaded biquad structure (series of second order filters put back to back). The filter can be considered ...
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0 answers
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Are IERS/EOC's UT1-UTC data averaged for tidal variations in error?

As long negative leap second is more probable than positive for do any prediction - indeed under condition earth's rotational behavior will be same as in last years - you need UT1-UTC data. ...
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1 vote
1 answer
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How to convert real BPF to complex BPF

Suppose if I have a real BPF (band pass iir filter with co-efficients of numerator and denominator), can one get the complex BPF filter coefficients using these ? Real BPF will be one sided and ...
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1 vote
1 answer
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I do not understand the frequency calculation used in the construction of this IIR digital Butterworth Low pass filter using MATLAB

The question is to design a Low Pass Butterworth IIR Digital filter. The following code below has the specifications with $A_p$ being the passband attenuation, $A_s$ the stop band attenuation, $f_{pb}$...
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0 votes
1 answer
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How to implement the direct form of FIR filter if in the transfer function there is no poles and power of z's are positive?

I confuse about the implementation of the FIR filter with no poles. If the transfer function is given in the form $$ H(z) = 1+az^{-1}+bz^{-2} $$ direct form implementation is just delay operator ...
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0 votes
1 answer
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How to determine the transfer function of the second order FIR filter?

I need to find the transfer function of the second order FIR filter. I searched a lot in the standard textbooks, but I could not get the mathematical expressions and derivations. I want that the zeros ...
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1 vote
1 answer
76 views

How can I reverse engineer the parameters of this butterworth filter?

I am trying to develop an application which will need a bandpass filter. The sampling rate is 30Hz, and the frequency range I'd like the filter to preserve is: 0.5Hz-4Hz. I've used mkfilter to ...
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2 answers
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Range of difference equation coefficients in practical FIR/IIR filters

In the design of practical FIR and IIR filters using difference equations, what is the range of coefficients that is employed for practical filters. How many orders might be used? What might the range ...
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0 votes
1 answer
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question about time delay of practical filter design with sampling frequency

most system have 48khz and if i have 40tap low pass fir filter that cutoff freuqency is 300hz, filter delay is 1/48000*20 = 0.0004s but the frequency resolution is very sparse and i think if the ...
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1 vote
2 answers
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Minimal group delay filter to remove harmonics but preserve fundamental

I have a signal that contains energy at a fundamental frequency (60 Hz) plus significant energy at harmonics (2nd, 3rd etc up to 15th). The signal is sampled by an ADC at 1920 Hz. I want to construct ...
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7 votes
2 answers
421 views

High Dynamic Range FIR Filters

Related to this question on using the Windowing method for FIR filter design versus the optimized algorithms such as least squares (firls in MATLAB, Octave and ...
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1 vote
1 answer
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GNU Radio Low Pass Filter doesn't work as expected with different transition widths

I'm new to GNU Radio and signal processing. I don't know if the following is a simple question, but I have been scratching my head about it. I created a simple flow graph with a random source (0-3) ...
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-1 votes
1 answer
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Modelling and testing fixed point IIR filter with freeware tools

I understand from this other question that prior to implementing a fixed point IIR filter on a particular microcontroller target it's best to create a model using a DSP tool and compare the output to ...
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2 answers
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Issue Understanding Time Delay of a Digital Filter

I am new to the world of digital filters and am educating myself with the book Introduction to Digital Filters by J.O Smith III,. The author derives the frequency response of a very simplistic filter: ...
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4 votes
2 answers
899 views

Implementing a Butterworth Filter Manually in C/C++ via Second Order Sections

Short background: I want to implement a lowpass butterworth filter in C/C++. The end goal is to use this in a low-latency Python program, for which of course ...
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0 answers
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Pressure signal

I have got an raw file which has pressure and time and temperature format and after coding I have got the plots but my main task is to analyse the data and understanding the influence of Bessel and ...
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1 answer
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What is the warm-up period of a Butterworth filter?

I am not sure if I use the correct term which may be the reason why I was not able to find the answer, but what I mean by the warm-up period is the number of samples required for the filter to produce ...
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1 answer
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Find the output signal in a Low Pass Filter for a given cutoff frequency range

I have a scenario where 𝑥(𝑡)=2⋅sin150𝜋t +sin250𝜋t and g(t)=𝑥(𝑡)sin250𝜋 . The signal g(t) is passed as input through an ideal lowpass filter with cutoff frequency(fc)= 300𝜋 and passband gain= 3....
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-1 votes
1 answer
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What is the duration of the transient response in FIR filters

I have read that for FIR filters, the duration of the transient response is equal to the order of the filter. But, for linear phase FIR filters constructed with the windowing method, the transient is ...
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1 vote
0 answers
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implement bandpass filter on complex valued signal? (C++)

I want to filter out complex valued samples - Bandpass filter. I have 100 complex samples and I wish to filter out a range of frequencies from it, as you can see in the result of the FFT, there are 3 ...
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0 votes
1 answer
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Composing digital filters

I'm interested in composing filters for realtime audio processing on an microcontroller (MCU). Ideal frequency response is unity as a default, with deviations up and down at specific freq-domain ...
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0 votes
4 answers
120 views

Why do FIR linear interpolators have linear phase?

I wonder why linear interpolation is a linear-phase FIR filter. In fact, I am reading Dr. Rice's great book "Digital Communications; A Discrete-Time Approach," and he mentioned on page 466 ...
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1 vote
1 answer
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Expression of output for discrete time causal filters

I have a question about the expression of the output of a discrete time filter described by its impulse response $h(k)$. Looking at the defintion of a discrete filter with input $u(k)$ and output $y(k)...
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2 answers
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Pulse-shaping FIR filter

I understand that pulse-shaping is performed to limit the bandwidth of the transmitted signal, but I would like to know how pulse-shaping can be implemented using an FIR filter.
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Subband Tuning in Matlab

Suppose you have an i/q stream with a sample rate of 20 MHz. You want to bandpass filter a 1 MHz bandwidth (ie passband from 5 to 6 MHz). You then want to heterodyne that 1 MHz chunk. How would you do ...
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-2 votes
1 answer
91 views

What is the transfer function of the filtfilt?

I designed a Parks McClellan filter to design a lowpass filter. First, I created the order of the filter with firpmord(). Then I designed the filter with firpm() and created the impulse response. I ...
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