# Questions tagged [frequency]

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

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863 views

### Detect presence of a specific frequency (or lack thereof)

I know very little DSP beyond an intro undergrad course. I was looking to write a C algorithm that takes ADC samples and determines if a specific frequency is present (in the range of 100KHz); not ...
223 views

### Measuring the “frequency stability” of a signal

I'm thinking about ways to automatically identify and analyze lots of musical instrument samples, and would like to find the part of the sample that's the most stable in frequency, without any ...
16k views

### How to make frequency axis for even and odd FFT length?

Can I get help on how to make frequency axis going from negative frequency to positive frequency, (in Hertz), that will be the x-axis in an FFT result, but given either an even length FFT, or odd ...
126 views

In the documentation for the [XAudio2 filter parameters] it mentions Filter radian frequency calculated as (2*sin(pi*(desired filter cutoff frequency)/sampleRate)) ...
2k views

### How do optical illusions work (photo mosaic) from a signal processing perspective?

Hello fellow investigators I have two question about optical illusions 1) A photo mosaic is something like this: What are the signal processing principles behind our eye merging the many tiny ...
2k views

### Signal matching: How to quantify the difference between two signals of varying frequency

I have two waves, and I would like to quantify the difference between them. They are exponential sine waves where the frequency decreases with time. I'm interested in the difference in decay ...
19k views

### What is the bandwidth of a (real) sinusoidal tone, and pulse?

I would like to know how to go about calculating the bandwidth of: A constant (real) sinusoidal tone A (real) sinusoidal pulse. The question is as simple as that, but I am having a hard time with ...
821 views

### How to Shift Carrier Frequency in QAM Signal?

If I wanted to apply a 100Hz frequency shift to a QAM signal with a 500MHz carrier frequency, I would Demodulate it at the carrier frequency Apply a frequency shift to the original signal Modulate it ...
911 views

### differences in fundamental frequency/pitch between music and speech

I am developping a program, that extracts very expressive frames from a video (meaning: frames, which could summarize a video) for a university seminar. One of my ideas was, to analyze the audio data (...
3k views

### Why can Quadrature Demodulation demod a Frequency Modulated Signal?

I use a Quadrature Demodulator in my SDR application, which is defined as: $\angle (S_n, S_{n+1})=arctan(S_{n+1}*\overline{S_{n}})$ So practically its amplitude is the angle between two Samples $S_n$...
13k views

### How do I create a frequency vs time plot?

I'm a chemical engineer, not an EE, so this is a bit difficult. I'm trying to figure out how to take amplitude vs time data and transform it into frequency vs time. My first instinct is to slice my ...
7k views

### Determining Frequency and Period of a wave

I'm gathering temperature data from a refrigerator. The data looks like a wave. I would like to determine the period and frequency of the wave (so that I can measure if modifications to the ...
62k views

### Why Carrier signal can't have frequency less than Message signal

I know that why we use Carrier of high frequency to send message signal over a long distance, when the frequency is low , energy will be obviously low. To increase the energy of the signal we need to ...
1k views

### On using eigenvectors to estimate a signals' fundamental frequency, via MUSIC

Context: (Disclaimer: This is NOT a comm problem). I am trying to estimate the fundamental frequency of a real, periodic signal. This signal, was constructed by match filtering a raw signal, to that ...
20k views

### Why are sidebands generated in AM and FM?

When the signal is modulated onto the carrier in the electromagnetic spectrum, that signal occupies the small portion of the spectrum surrounding the carrier frequency. It also cause sidebands to be ...
12k views

### If Digital Signal has frequency components then why we don't use it

As we know there are two kinds of signals: analog signals and digital signals. And there are two common techniques for multiplexing the signals: Time Division Multiplexing (TDM) and Frequency ...
610 views

### Books that explain DSP well to those not directly in engineering?

I do work with computer graphics and am dipping my toes into ray tracing. That field involves a good number of the subjects covered in DSP (Fourier transform, time vs frequency space, etc) but I was ...
4k views

### I need advice about how to make an audio frequency analyzer

I just need some clarification of some very basic aspects of creating a frequency analyzer. I am writing a c++ program, so far it is just a media player, with a custom explorer. You can make ...
454 views

### Extraction of non-sinusiodal repetition rates

I have an auto-correlation function that was generated from a signal, and I am trying to extract its 'repetition rate' in order to calculate the dominant frequency of the pulse, but I am not exactly ...
3k views

### period of this signal

it could be a donkey question but I'm a little confused. I have this signal $w(t)=sin({\pi}0.1f)$. I have to calculate the period of this signal. $w(t)=sin(2{\pi}\frac{1}{20}f)$ the period of this ...
1k views

### Why does a wave continuously decreasing in frequency start increasing its frequency past the half of its length?

I'm trying to programmatically generate a wave (sine or square) with a continuously decreasing frequency. To do so, I simply multiply the starting frequency for a decreasing value, that linearly goes ...
21k views

### How to shift the frequency spectrum?

Lets say we have a spectrum ranging from -X MHz to +X MHz. I would need to correct the frequency error in the spectrum by shifting the zero component to the middle (0 Hz). If the output (the ...
2k views

### Efficient frequency offset estimation of known signals

Let's say that my receiver will be receiving known data signals that range from the very simple (tone) to the complex (known data sequence that is modulated (PSK/QAM/OFDM/etc.)). What are the most ...
4k views

### What's the best criterion for determining a frequency peak?

I'm writing an algorithm that analyzes results of discrete Fourier transform (DFT). The algorithm should detect amplitude peaks in predefined ranges of frequencies. This is an example of such a peak: ...
278 views

### Procedural wave generation, frequency shift issue

sorry for the long post but I want to try and get all the details in here in hopes it will help. I've been working on building a procedural audio system for use in XNA projects. First this is general ...
1k views

### Does down-mixing a signal before taking the fourier transform aid in signal detection?

Let us assume that we have a narrowband signal $s[n]$, at frequency $f_1$, and let us further assume that this $f_1$ is just below $\frac{f_s}{2}$, where $f_s$ is the sampling rate. Furthermore, let ...
1k views

### Noisy Frequency Estimation using Hilbert Transform

I'm looking for a way to estimate instantenous frequency with low time-variation. The following MATLAB function (save as test_fest.m) does this using the Hilbert ...
29k views

### What is the Gabor filter? And what are its main uses?

I'm doing research on the Gabor filter. When I Googled it, I found very long and complicated articles. Can anyone help me to find a simple explanation about it, or recommend a website or article to ...
245 views

### Modeling spring oscilliations with electric noise (50 hz)

I have Analog to Digital converter from which I get data of measurements of 1kg load. The aim is to model the simple spring-damper system, so that after entering correct initial data (x[0] = a, x'[0] =...
13k views

### Is there an algorithm for finding a frequency without DFT or FFT?

I was looking in the Android app store for a guitar tuner. I found a tuner app that claimed it was faster than other apps. It claimed it could find the frequency without using the DFT (I wish I still ...
2k views

### Find h[n] using DTFT properties

Using the DTFT property, find h[n] of a system where: Is it an FIR or IIR system?
2k views

### Detecting drum bpm in a noisy .wav file

I am looking for algorithm(s) to solve the following problem: Given a noisy .wav sound capture (some wind + friction noise on the microphone), how to detect the BPM of a soft drum beat? I have ...
2k views

### Apply wavelet transform to analyse EEG signal

I would like to apply The Morlet wavelet transform to analyse my EEG signals. I have many short signals each is only 1 min long. and they all recorded in 30Hz. I have Two questions: In the Morlet ...
303 views

### Angle modulation spectrum

Is angle modulation spectrum always discrete or this property only holds for periodic modulating signal?
4k views

### Choices of convention and notation for the Fourier transform?

The definitions of the Fourier transform and inverse Fourier transform I learned in college were $$F(j\omega) = \int_{-\infty}^{\infty} f(t) e^{-j\omega t}\ dt$$  f(t)=\frac{1}{2\pi}\int_{-\...
213k views

### What is meant by a system's “impulse response” and “frequency response?”

Can anyone state the difference between frequency response and impulse response in simple English?
633 views

### Weird results out of fourier transform of unknown signal, what am I doing wrong?

It has been a long time since I studied engineering, please forgive my mistakes. I got data sampled from a digital accelerometer. It is sampled at 20 hz, then collapsed into 1 second epochs. The data ...
82k views

### What is the physical significance of negative frequencies?

This has been one of the holes in my cheddar cheese block of understanding DSP, so what is the physical interpretation of having a negative frequency? If you have a physical tone at some frequency ...
1k views

### What mathematical model of audio can make possible pitch shifting of individual notes in (timbrally complex) polyphony?

My question is: What mathematical model of polyphonic sound can make possible the changing (i.e. pitch shifting) of individual musical notes in a multi-voice-in-single-channel audio recording of a ...
287 views

### Finding the input bit rate of an analogue input

Suppose I have 4 of 300bps synchronous digital input and 1 of analogue input with a bandwidth of 500Hz. The analogue input is sampled at 4bit using PCM. All the channels are multiplexed with TDM. As ...
392 views

### How can I calculate the frequency using different color bands?

Let's say that I have a 1 dimensional signal that has data which comes from one of 2 different spectral bands. The measurements come evenly mixed between the two bands. I'm interested in a method of ...
The Fast Fourier Transform takes $\mathcal O(N \log N)$ operations, while the Fast Wavelet Transform takes $\mathcal O(N)$. But what, specifically, does the FWT compute? Although they are often ...