Signal Processing Stack Exchange
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Taking audio frequency and picking out peaks (Peak Detection)

So I have a unique challenge. I want to take an audio file, and pick out the peaks in the samples and plot that onto a graph. Each point based on the amplitude/pitch(?) will be represented as either a small dot (lower amplitude) or a bigger dot…
Johan Steyn
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Calculating values of frequency bins in Python

I have to use FFT to determine the period of waves inside a signal. After applying FFT on a window of 10000 point from a signal, I get something like this: What I don't understand is that FFT is supposed to return frequencies, but if the input is…
Hamza Tahiri
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Python butter filter: choosing between analog and digital filter types

I have a system that performs wireless sampling of data about every 7.5ms (133Hz). Due to it being wireless, I get occasional data drop out. I want to construct a LP butter filter with cut-off frequency of 10Hz using Python's scipy butter method and…
Geko
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What Is the Difference between RLS, LMS and Wiener Filter? When Is One Preferred Over Another?

I'm dealing with a channel equalization problem where the channel is modeled as a WSS process. I understand LMS utilities a Wiener-like approach, ie it converges to the optimal (wiener) solution. I understand RLS converges to the normal solution,…
Marco Datola
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Why is aliasing inherently non-linear?

E.g. when having 2 signals $x(t)$ and $y(t)$ and transforming each one with adding their spectra, the operation is linear, as the result would be the same as the transformation of $(x + y)(t)$. Even when looking at the sampling series, each of the…
Starhowl
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The necessity of null subcarrier in OFDM?

In looking to LTE specifications, with the subcarrier spacing $\Delta f = 15 \textrm{kHz}$, for bandwidth $10 \textrm{MHz}$, fft size $N_{fft} = 1024$ that needs a sampling rate $F_s \geq 1024 \times 15\textrm{kHz} = 15.36 \textrm{MHz}$. The useful…
AlexTP
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Simplest All Digital GMSK Modulator

How to simply implement an all digital GMSK modulator with no multipliers? The implementation approach should be applicable to GMSK modulation with $BT=0.5$ or less (where intentional ISI is introduced to obtain higher spectral efficiency). By "all…
Dan Boschen
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Flat fading criterion of OFDM subcarrier spacing

I have always thought that the OFDM subcarrier spacing $\Delta f$ is chosen such that not too small because Doppler spread can destroy subcarrier orthogonality not too large to avoid Cyclic Prefix (CP) overhead because OFDM symbol period $T_u =…
AlexTP
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Filtering - multiplication in frequency domain

I am trying to create a simple low pass filter, but I have got what I consider a surprising result when looking at the frequency response of a simple Butterworth filter. I have copied much of the example below from this other post. I have added some…
James Dilworth
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Is interpolation of an audio signal to increase frequency resolution possible?

I apologize if some of what I ask is not entirely correct, I'm new to this field, but extremely interested. I have an Audio signal of sample rate 44.1 kHz that I want to segment into 30 frames, and get the DFT of each frame to find the magnitude of…
echolocation
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Nyquist's Stability Criterion and Cauchy's Argument Principle

Background: Nyquist's Stability Criterion for linear-time-invariant systems makes use of Cauchy's argument principle to determine if any zeros in the characteristic equation are in the right-half plane (positive real roots), given a closed loop…
Dan Boschen
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RMS values above 0 dbFS?

I wonder why several RMS meters I'm using for music production show RMS values above 0. For example, when using an input signal with a constant DC of 1 (0 dbFS), I get these results, although Wikipedia says that in such cases, the RMS is equal to…
Sebastian
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Is this signal perfect reconstructable?

The question is as follow: Let me do the analysis: The downroad first: \begin{align} X_1(z) &= z^{-1}X(z)\\ X_2(z) &= \frac{1}{2}\left\{X_1\left(z^\frac{1}{2}\right)+X_1\left(-z^\frac{1}{2}\right)\right\}\\ X_3(z) &= X_2(z^2) =…
stander Qiu
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Designing an IIR to generate a specific data sequence

I know that it's possible to design an IIR with specific poles and zeroes to create specific frequency responses. Is it also possible to design an IIR such that when you give it an impulse, it generates values of a desired sequence? Or at least a…
Alan Wolfe
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White noise DC component

I'm really new to DSP, I'm actually studying Computer Science and took an elective on DSP so my knowledge is pretty limited. I've learned that pure white noise signal for example has all possible frequencies, that means that it also has zero…
Evgeny
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