Questions tagged [magnitude]
The magnitude tag has no usage guidance.
63
questions
17
votes
3answers
7k views
Why are magnitudes normalised during synthesis (IDFT), not analysis (DFT)?
In most examples and FFT code that I've seen, the output (frequency magnitudes) of the forward DFT operation is scaled by N -- i.e. instead of giving you the magnitude of each frequency bin, it gives ...
7
votes
2answers
44k views
Power spectral density vs. FFT bin magnitude
What's the difference between these? Both are measurements of some form of signal power, but surely there's some difference between the power they are measuring?
5
votes
1answer
5k views
How does zero-padding affect the magnitude of the DFT?
Let's simulate sinusoids of two frequencies using the following Matlab code:
...
4
votes
1answer
11k views
Identifying the magnitude and impulse response from pole zero plot quickly
I have an exam next week and it's verty certain that a task of this kind will be there.
Are there some good tips how to match the right pole zero plot to the right responses? No proof is needed in ...
3
votes
1answer
20k views
Energy calculation in frequency domain
I was just wondering... The formula I learned to calculate the energy of the signal is expressed in the time domain:
$E_x^{\text{time}} = \sum_{n=-\infty}^{\infty} |x[n]|^2 $
Then, what does the ...
3
votes
3answers
4k views
Adequate representation of frequency domain amplitude/magnitude of FFT of a signal
I'm quite new to the subject and am having fun playing around with the FFT. What I am currently doing is trying to sample an audio signal and display its frequency spectrum at the same time. This ...
3
votes
3answers
3k views
recover image by only magnitude of image fourier transform
I have a image and I want calculate fft2 of it, after it I want recover image only by magnitude of it. how can I achieve this work?
...
3
votes
1answer
80 views
Given a plot of both the magnitude $|H(\omega)|$ and its angle, How can you find the $H(\omega)$?
I'm specifically trying to use an inverse Fourier Transform to find $h(t)$, but I'm finding it difficult to get $H(\omega)$ in the first place.
I'm under the impression from my textbook that $H(\...
3
votes
1answer
258 views
Calculating phase response of maximum phase filter using Hilbert Transform
Given only a magnitude response $A(\omega)$ of a minimum phase filter, one can calculate the phase response using the Hilbert Transform:
$$θ(ω) = -\mathcal{H}\{\ln(A(\omega)\}$$
This paper suggests ...
2
votes
2answers
71 views
Phase response of $H(f)=e^{-j2{\pi}ft_0}$
Given is the impulse response: $$h(t)=\delta(t-t_0)$$.
I calculated $$H(f)=e^{-j2 \pi ft_0}=|H(f)|\cdot e^{j\varphi(f)}$$.
Now, the magnitude response of $H(f)$ is:
$$\begin{align}
|H(f)| &=\...
2
votes
3answers
137 views
Matlab IIR cheby2 bandpass, problems with Magnitude
I am trying to implement an IIR bandpass in Matlab. There are two things I don't understand. But first of all, let me post the code.
...
2
votes
1answer
124 views
Why harmonic components appear only after a certain level when a signal is clipped?
I recently observed this phenomenon that when a signal is clipped the harmonics start to appear only after a certain level.
The Python code to reproduce the effect is given below. The signal has 3 ...
2
votes
3answers
44k views
How to compute magnitude and phase response from transfer function in Z-domain?
I have a transfer function $$H(z)=\frac{1+1.2z^{-1}+0.8z^{z^-2}}{1-0.9z^{-1}}$$ from which I'm supposed to sketch the magnitude and phase response. I know that you can transform $z=e^{j\omega}$ to get ...
2
votes
1answer
450 views
Plot Magnitude from RBJ Biquad
Currently I'm working out plotting biquads in a VST/AU plugin and have problems with the graphics part. I posted in several forums but haven't got a really useful answer for this case.
First, tell ...
2
votes
2answers
172 views
Frequency response of a microphone using a sine sweep
I want to determine the frequency response (magnitude, phase) of a microphone. I have another "good" reference microphone whose frequency response I know.
I understand that I can use a good speaker ...
2
votes
3answers
753 views
How do I calculate peak amplitude of the signal components after zero padding and FFT?
I am learning about DFT and trying to apply it to some audio processing. I am new to DSP but experienced in programming and have some background in math and physics. The FFT algorithm I use (lomontFFT)...
1
vote
3answers
119 views
$e^{j\omega}$ on unit circle
I am new to DSP, and I'm self studying. I am confused about the magnitude of $e^{j\omega}$ - where $\omega$ is the normalized angular frequency - when we are on the unit circle.
According to the ...
1
vote
1answer
4k views
retrieving original data from phase and magnitude of Fourier transform
I use this snippet of python code to transform data to Fourier phase and magnitude and then retrieving original data.
...
1
vote
3answers
2k views
Fill matlab “ellip” function through transfer function magnitude response
The matlab "ellip" function can be used to design the unquantised coefficient set.
From matlab website:
$ [b,a]=ellip(n,Rp,Rs,Wp) , $
n: order of filter
Wp: normalized passband edge ...
1
vote
1answer
590 views
Spectrogram with square or non-square magnitude of STFT: power vs. magnitude
As seen in this question and answer, to do a spectrogram, it's common to plot either:
the square magnitude $|\text{STFT}(\text{frame}, \text{bin})|^2$ ("power spectrum")
the magnitude $|\text{STFT}(\...
1
vote
2answers
185 views
how to make fft ignore phase shift when only interested in magnitude
I have a signal that consists of a sine wave, on which I apply a rectangular window and then an FFT. I'm only interested in the magnitude of the sine wave, and I want it to stay the same even if the ...
1
vote
1answer
169 views
Obtaining the magnitude of the frequency response by plugging $e^{jω}$ into the z-domain transform function?
I am reading a text on discrete signal processing, which states that the frequency response of a signal can be obtained by plugging the value $e^{jω}$ into the z-domain transfer function $H(z)$. In ...
1
vote
1answer
60 views
Calculate aliasing of $x_a(t) = \cos{(2\pi300t)} + \cos(2\pi600t)$ when sampled with $F_s = 1000$
I'm asked to sample the signal
$$x_a(t) = \cos{(2\pi300t)} + \cos(2\pi600t)$$
with sampling frequency $F_s = 1000$ and plot the magnitude spectrum for the resulting sampled signal.
My thinking is ...
1
vote
2answers
281 views
Zero padding and 2D Fourier transforms: how does zero-padding affect phase?
It's pretty clear that zero-padding an image before performing Fourier transform simply enlarges the magnitude image (stretching it to the new, padded size).
What I can't understand is how it affects ...
1
vote
1answer
47 views
How would I find the function given the magnitude plot and the phase response?
I'm wondering how I'd find the Fourier Transform X(jw) given the following information:
My understanding is that the expression for the continuous time fourier transform (CTFT) is magnitude(CTFT)exp(...
1
vote
1answer
2k views
Magnitude of function in $z$ domain
I am newbie to $\mathcal Z$-transform, I searched to find the magnitude of a function in $z$-domain, but I couldn't find anything, for example when we have
$$
H(z) = \frac{z-3}{z-0.5}
$$
How do you ...
1
vote
1answer
404 views
How can resonance be added to a fractional order Butterworth low pass
I am interested in how to add resonance (Q) to the magnitude response of a Butterworth low pass when it is expressed in the form:
$$
G^2(\omega)=\frac {1}{1+\left(\frac{\omega}{\omega_c}\right)^{2n}}
...
1
vote
2answers
463 views
Averaging Multiple Magnitude Spectra
I'm currently trying to implement some of the methods found in this paper on intelligent equalization - http://www.aes.org/e-lib/browse.cfm?elib=16792 -
The first part of the process is to build a "...
1
vote
1answer
108 views
Energy definition for Autocorrelation lag 0 and lag 1 for complex signals
I am studying the role of an auto-correlation matrix for random signals and the difference of energy between a lag 0 and lag 1 matrix.
Consider a complex input signal $x(k)=[x1,x2]^T$ and $x(k-1)=[x0,...
1
vote
1answer
874 views
Magnitude response and DFT normalization
Suppose I have an FIR denoted h that represents the impulse response of a system. Using MATLAB syntax (for convenience and brevity),
What does ...
1
vote
1answer
681 views
How to reconstruct signal of its phase and magnitude functions?
I have two continuous periodic (a period of $2\pi$) functions which belong to the phase and magnitude of Fourier transform of a signal, how can I reconstruct the original signal? What kind of ...
0
votes
2answers
5k views
Plotting the magnitude response of a filter?
I have designed a second order butterworth filter.
Sampling frequency: $4\textrm{ kHz}$, Cut-off frequency: $500\textrm{ Hz}$
$$e = \tan\left(\frac{\pi \times f_c}{f_s}\right) = \tan\left(\frac{...
0
votes
2answers
23k views
How to plot magnitude and phase response by hand if I have the Transfer Function?
I have the transfer function of the system, which is:
$$H(z) = \frac{1-z^{-1}}{5(1+2z^{-1})}$$
How do I sketch the magnitude and phase response?
I'm sorry for the bad formatting, it's my first time ...
0
votes
1answer
78 views
Does a filter need to completely attenuate high frequencies to be considered low-pass?
I'm looking at a system with a frequency response that is: $$H(e^{j\omega})=\tfrac{1}{4}(2\cos(\omega)+\cos(2\omega)+2)$$
I think the magnitude of this system looks like this (not sure what is the ...
0
votes
1answer
593 views
Recovering signal from magnitude and phase of FFT
I'm trying to code the basics of an analysis-synthesis system on MATLAB, but I'm getting incorrect results. From the Wikipedia page:
$$
X_k=\lvert X_k\rvert e^{i\angle X_k}
$$
Here's a simple MATLAB ...
0
votes
2answers
396 views
phase, magnitude, audio file and information
I've been doing some thinking lately. I know that for image files a larger portion of information is contained in the phase of the signal. How does that go for the audio? Does the same hold or is the ...
0
votes
1answer
131 views
Sketching Phase Spectra Using Group Delay and Magnitude Spectra Informations
I have only magnitude spectra and group delay information and I need to sketch phase spectra from this information. For example, group delay is given like this: $\tau_{g}(\omega) = c$ where c is a ...
0
votes
1answer
269 views
Change of bin magnitude when phase of signal changes when doing FFT?
I am working on an implementation in which I need to apply an FFT to determine which of 4 frequencies are present in a signal.
I am doing a 64 point FFT on a buffer which only is partly filled (the ...
0
votes
2answers
52 views
Is it valid to calculate the magnitude, power, and phase of a real time-domain signal without converting it to the frequency-domain?
I would assume you perform the calculations the same way, but since there would be no imaginary component because the signal is not complex it would be simpler:
...
0
votes
2answers
183 views
Phase information from product of complex conjugate transfer functions
For an input signal $x(t)$ and output signal $y(t)$ through an LTI system I $H(t)$ I have found and interesting property that concerns signals' power spectral densities:
$${\lvert H(\omega)\rvert}^2 =...
0
votes
1answer
57 views
Computing real signal with minimum absolute values from even magnitude spectrum
I want to derive a real audio signal from an arbitrary even magnitude spectrum.
The phase spectrum affects the values of the signal in the time domain; for example, a phase of 0 for all frequencies ...
0
votes
1answer
76 views
zero-phasing frequency components while keeping the same magnitude, in Matlab
How is it possible?
I was thinking of taking just the real part of the DFT of my signal (isn't that zeroing out phases?) with
real(fft(X))
but the magnitudes ...
0
votes
1answer
752 views
sketching magnitude of frequency response of H(z)
I am trying to plot the magnitude of H(z), I got it to factore, and would like to sketch its plot of magnitude. But I am have trouble evaluating the function.
$$
H(z)= \frac{(1-2z^{-1})(1+0.5z^{-1})(...
0
votes
1answer
257 views
Interpreting magnitude of DFT results
I'm working on creating a simple program to render spectrograms like this one. In this plot, the X-axis is time, the Y-axis is frequency, and the color represents the magnitude of the DFT at that ...
0
votes
2answers
1k views
Magnitude Spectrum, different magnitudes same amplitude
When the following code is written,the resulting magnitude spectrum shows magnitude values represented by two peaks is different even though they have the same amplitude. why is that?
a fast reply ...
0
votes
2answers
844 views
Matching an LPC Magnitude Spectrum to FFT Magnitude Spectrum
I'm trying to get an LPC magnitude spectrum to match to an FFT magnitude spectrum. Basically I want the peak height in the LPC Spectrum to match the peak height in the FFT Spectrum.
Thanks to ...
0
votes
0answers
32 views
FFT frequency-magnitude not correct when a positive gain EQ point is applied
I have a measurement system, which applies a log sine sweep as stimulus to a DUT and records the return signal.
I then extract the impulse response, and perform an FFT on this to examing phase and ...
0
votes
1answer
53 views
Correctly scaling FFT of different lengths
I have been looking at using two FFTs of different lengths and displaying the output magnitudes on the same graph (a shorter length window for the higher frequencies, and a longer one for lower ...
0
votes
0answers
39 views
Magnitude attenuation by a filter
I have a filter, with coefficients given by W=sin((2*pi*2*Ff*k/Fs)/(2*pi*2*Ff*k/Fs))*h(k), where Ff is the filter reference frequency, k runs from -N/2 to N/2 (N is the order of the filter), Fs is the ...
0
votes
0answers
13 views
Wavelet Analysis Magnitude Scale
I am trying to plot magnitude against frequency averaged over a time window.
To do this I make a morlet wavelet Filterbank. And multiply the dft of each kernel by the dft of my incoming data set.
...
