Questions tagged [frequency]

Frequency in signal processing is the number of cycles (of the signal) per second.

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815 views

How to find PSD (Power spectral density) of spatial data

I have profiled a surface, measuring the height of peaks and troughs at 0.02mm intervals. I have 1501 data points, the below listed as an example: $$\begin{align} x &= 0\,\mu\text m & y &...
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175 views

Positive and negative frequencies: how to prove they are independent?

This seems to be quite a basic question but is there some detailed proof why interference power (i.e., power spectral density) coming from the positive and negative frequencies are independent? I am ...
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254 views

Determining the Nyquist rate of signals added and multiplied together

Suppose I have a signal in the frequency domain $x(\omega)$. Suppose I know that its Nyquist rate is $\omega_0$ (and let $\omega_m$ be the its maximum frequency). I need to get the Nyquist rate of $...
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360 views

Power/Amplitude Response of a system

I am currently looking over filters and understand the frequency response of a system, e.g. a low-pass filter. However I am confused by the 'Power/Amplitude response' of a system as detailed in my ...
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180 views

Extract parameters of a single harmonic

Context I need to extract the parameters of a single harmonic in a signal. For instance if $$ x(t) = A \sin (\omega_0t + d_0) + B \sin (\omega_2t + d_2) $$ then $f(x, \omega_0) = (A, d_0)$. This ...
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645 views

How to detect decaying oscillations in a signal

I have a sampled signal which contains (among other things) some damped oscillations. From the underlying theory I have reasons to believe that it can be characterized by some specific frequencies of ...
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1answer
155 views

How do I measure frequency of an audio file into an array?

So I know how to plot fft the audio file within Matlab and a window pops up. My question is, what next? I want to know how to go about measuring the frequency(s). I have two similar audio files, of ...
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2answers
984 views

Compressing a time-domain signal in the frequency domain Matlab

I'm new to frequency domain analysis. Let's say I have a frequency domain representation from a time domain signal. What I want to do is taking frequencies with a low amplitude out of this frequency ...
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417 views

Aliasing Square Wave

I'm having a really weird issue with generating waveforms from frequencies C1 to C8. When I generate sine waves, everything sounds good; no problems whatsoever. However, when I generate a square ...
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2answers
3k views

The relationship between downsampling and frequency resolution

I am having trouble understanding a concept that I have seen in many published papers. For example, in this paper (http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0082748) they wrote ...
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1answer
122 views

How can a signal have two maximum frequency components?

$x(t)$ can be exactly reconstructed from its samples at $\omega_s = 10 \textrm{ rad/sec}$. My conclusion is that the maximum frequency component in $x(t)$ is $5\textrm{ rad/sec}$. But I'm being told ...
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971 views

Sampling frequency of audio

Based on what we choose sampling frequency when sampling some song? Do we use Nyquist–Shannon sampling theorem, or maximum sampling frequencies are pre-defined, so it will never come to aliasing ...
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3k views

What is the difference between a'mixer' and a ' multiplier' used in modulation process?

I am not sure if it is valid to conclude that a mixer produces a difference/sum of frequencies at output ,while multiplier produces multiples of frequency at its output. I am keen to know how far I ...
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502 views

Difference between these frequency response curves

I am thinking about a simple mass-damper system response. Most single DOF systems show a frequency response plot that looks like this: Note how increasing the damping ratio always reduces the output ...
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292 views

EEG signal processing with sampling frequency

What is the relation between sampling frequency and the frequency of the signal after sampling? For example sampling frequency is 100 Hz, that is the signal contain maximum frequency of 50 Hz. Then ...
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697 views

Why does resampling change the frequency range?

I am currently working on a set of .wav files which, unfortunately, do not have the same sampling rate - I need to resample them for the purpose of feeding them to a neural net. So - using Sox I ...
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1k views

How to remove 50 Hz frequency noise from a PCM file?

Are you kind to tell me the odds or the means by which should I grab a clean signal with the $~50 \mathrm{Hz}$ hum removed using just programming? I managed to make a program in Visual-C that ...
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1answer
4k views

Calculating a signals frequency when given the number of samples

This place has been great in helping me to understand my online image and signals class! I've moved on to another question and wanted to see if I'm correctly grasping the subject. The next question ...
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417 views

Capturing the sampling rate from a basketball being dribbled

I'm taking an online image and signals class and the structure is absolutely horrible. I'm wondering if you can provide me hints, or tips to solving the below question. I'm not looking for an ...
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2answers
107 views

Will decorrelating an audio signal help reduce interference patterns at low frequencies?

In live sound it is common to have a left/right sub-speaker configuration, which will produce an strong interference pattern in the audience area based on listener/sub-speaker locations. If the left/...
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2answers
717 views

How to pick a sampling frequency for Matlab fft

I am recording vibration data using an adxl335 accelerometer.I have ~50ms delay before i save a reading from this sensor so most probably each second i have ~20 readings. I verified that by checking ...
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1answer
119 views

Signal response in Frequency Hz from angular frequency

I have a filter whose respose I have in angular frequency. ...
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1k views

Audio frequency modulation algorithm

I have a digital audio signal (float samples). I need to apply the Vibrato effect to a signal. "Vibrato" is no common term, but it is the same as the frequency modulation. So, I need to modulate my ...
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1answer
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VIbrato (pitch variation) function

I'm looking for an algorithm for Vibrato audio effect for a cross-platform C++ program of audio processing. Now I use the realization from Chaotic-DAW sources. The problem is that Chaotic-DAW has a ...
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199 views

What are the implications of resampling the derivative of a signal with a higher frequency than the original signal?

Suppose I have a digital signal measured with sampling time, $T_s=1$ sec. If I take it's derivative, it will, naturally have $T_s=1$ sec. But what are the implications if I re-sample this derivative ...
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169 views

What does pre-emphasis $\alpha=1$ will do to a signal?

I am trying to understand pre-emphasis equation. $$ y[n]=x[n]-\alpha x[n-1]$$ Where $\alpha = 0.95$. My question is what does it mean if $\alpha = 1$?
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290 views

Find Natural Frequency $\omega_n$

You are testing a new device to determine its characteristics. You find the magnitude of its frequency response shows a peak at 500 Hz, and the measured overshoot of the step response is 40% of the ...
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251 views

how to find breakpoints of a signal based on the frequency of the signal

There are 4 cos signals with 10,20,30 and 100 Hz each. The main signal is the sum of those 4 and I have to create a low pass filter, on the main signal for the frequency's > 50 Hz. ...
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111 views

Resonance and Pitch classes

Suppose we denote the frequency of the note $\textbf{C}_{0}$ by $f$ then we know that $f,2f,3f,...$ are all resonating frequencies. However the frequencies $2f,4f,...,2^{m}f$ belong to the same pitch ...
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232 views

Is the book wrong? — How to sketch frequency response obtained from H(z)?

This question is directly related to digital signal processing, so I am asking here. How to sketch frequency response obtained from $H(z)$? I'm adding an example and its solution below. I did not ...
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42 views

Find unknown broadcast frequency

I'm very new to this stuff, so please excuse the dumb sounding terminology. I'm trying to capture the data from my elster smart hydro meter. How can I find its frequency (I know its between 902 and ...
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561 views

Relation between bandwidth and data rate

I have trouble understanding the following from wikipedia - Bandwidth (Signal Processing) A key characteristic of bandwidth is that any band of a given width can carry the same amount of ...
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2k views

Are there libraries for extraction of sound wave features?

I am looking help for my project for which I need C++ (or any other language) libraries useful for extraction of sound wave features like frequency, loudness, pitch and orientation. Using these ...
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1answer
192 views

Find minimum sampling rate of non-ideal notch filter

Old test problem: "You have been asked to design a real-time digital filtering system that eliminates a band of frequencies between 20 and 30 MHz but preserves everything else. The system uses an ...
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3answers
4k views

sampling rate for band pass signal

The sampling frequency for band pass signal which is having frequency from 4 kHz to 6 kHz(rectangular shape from 4 to 6 kHz), can I prefer the sampling frequency of 12 kHz(2*the highest frequency ...
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488 views

Determining frequency deviation FM

I am trying to understand the concept of frequency modulation. As written in Wikipedia, if I have a signal containing information $x_m(t)$ and I want to transmit it using frequency modulation, I need ...
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1answer
105 views

Sample Frequency - Recommended Practical Nyquist, Lower Used by majorities appications

Doubt1: What is the Lowest Sampling Frequency used by majorities sound applications. Is there limited frequency sampling lower than 8KHz In C/C++? Comment In Java I haven't detected any problem, but ...
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65 views

Retrieve frequency value of an 2D frequency spectrum

How do you retrieve the values of the frequency component occurring in a 2D freq spectrum? I have this, and if I wanted to know the values of the white dots. what should i do ? I apolgize ...
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1answer
52 views

Find the frequency of a pole (Discrete Form) [closed]

I am studying a Notch filter. I found its Transfer Function (in Z) and its poles. How can I find the frequency of theses poles (which corresponds to the cut-off frequency)? Thank you very much for ...
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1answer
88 views

Obtaining power spectral density without having knowledge about frequency bandwidth or sampling frequency of the signal in Matlab?

Is there a way to plot PSD of a signal which show true frequency amounts ( not normalized one) without having knowledge about frequency bandwidth or sampling frequency of the signal in matlab ?
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Doppler shift in time domain?

I have some clarifications required in this topic So initially I know that to shift a signal $X(f)$ by $f_0$ we need to take its inverse fourier transform and multiply it with a factor of $\exp(−j2\pi ...
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2answers
144 views

What is a note?

That simple. What is a note in digital signal processing? Is it a single value of y[n] in a system with a difference equation e.g. ...
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90 views

Given a real signal, increase modulation frequency

Lets say I receive the signal $$x(t)\cos(\omega_c t)$$ and I want to change the the carrier frequency $x(t)\cos(1.001\omega_c t)$ How can this be done? If I modulated it with a complex exponential, ...
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1answer
191 views

Why is discrete cosine preferred to FFT in neuroimaging GLM

High-pass filtering is often used in neuroimaging data analysis. Commonly, whenever a general linear model is fitted to the data (as for instance in statistic parametric mapping) a number of columns ...
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phase locked loop

I have seen that to get the phase angle of a signal, we have to use PLLs. this PLL is modeling in order to get the phase angle about one frequency, which is the free running frequency of the VCO. If ...
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2answers
1k views

Calculate Min/Max value of multiple sine waves added together

So I feel like this should be possible, I'm just not sure how to do it. Let's say I'm generating a signal with a sample rate of 10K samples/second. Then let's say my signal is comprised of X number of ...
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54 views

Using K-Space Filtering to Filter by Speed

I want to read waves with an electret consender microphone that are slower than the speed of sound, and I figure it would make those waves easier to identify if I could process out all waves moving ...
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1answer
49 views

Frequency of a DFT term

I've been wrestling with this question for way too long. I appreciate any insight you can offer. Thanks. If the $9$-point sample sequence $x(n)$ represents a time domain signal sampled at $48\...
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2k views

How to Flip Spectrum Around DC?

Is it possible to flip a signal's spectrum around DC? I have a simple spectrum that I made up (MATLAB code): ...
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8k views

How to calculate the frequency of a signal without knowing the sampling frequency using Matlab

I have a signal and I am using Matlab command pwelch to calculate the frequency of the signal, but the frequency I obtained is changed as I change the sampling frequency. For example, when using ...