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Exact RMS, Missed Troughs: A Sampling Trap in Python

Taking min(samples) is a tempting shortcut when building a waveform display. A twelve-harmonic example shows exactly what that shortcut can miss: 25 samples reproduce the signal’s RMS perfectly, yet t

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RishikantJul 3 · 8 min read

Revolutionizing 5G Networks with Intelligent Reconfigurable Surfaces and Deep Reinforcement Learning

The transition to fifth generation cellular networks marks one of the most significant leaps in telecommunications history. Unlike previous generations that relied heavily on sub six gigahertz frequen

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404 FoundersMay 2 · 10 min read

Can Your Router Actually See You? The Science of WiFi-Based Human Sensing

Deep learning, wireless signal processing, and Channel State Information (CSI) analysis have converged over the past few years to make it possible to estimate human pose using ordinary WiFi signals. T

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Jeongeun KimMay 1 · 5 min read

State Variable Filter: One Biquad Structure, Three Simultaneous Outputs

Transfer Function The State Variable Filter (SVF) implements three simultaneous outputs — lowpass (LP), highpass (HP), and bandpass (BP) — from a single shared pole structure. All three biquads share

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Jeongeun KimApr 26 · 6 min read

Butterworth Lowpass 4th Order: 80 dB/Decade Rolloff With Zero Passband Ripple

A 2nd-order Butterworth gives you 40 dB/decade. Double the order to fourth and you get 80 dB/decade — the same maximally flat passband, twice the stopband suppression. At fc = 1000 Hz with fs = 44100

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Jeongeun KimApr 26 · 7 min read

High Shelf Biquad: Boost High Frequencies Without Distorting Your Control Bandwidth

Every sensor signal chain has a frequency-dependent noise floor. Below the shelf frequency the signal is clean; above it, quantization noise, switching harmonics, or electromagnetic interference domin

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Jeongeun KimApr 26 · 7 min read

FIR Lowpass Kaiser Window: Linear-Phase Precision for Control Signal Filtering

Every IIR lowpass filter we have covered — Butterworth, Chebyshev, Elliptic — achieves steep rolloff at the cost of nonlinear phase, meaning different frequency components are delayed by different amo

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Jeongeun KimApr 22 · 6 min read

Low Shelf Biquad: DC-Range Gain Shaping Without Integrator Wind-Up

A pure integrator (pole at z = 1) delivers infinite DC gain and infinite wind-up risk. A low shelf biquad gives you the same low-frequency gain boost with a defined upper limit, no saturation algebra

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Jeongeun KimApr 22 · 6 min read

Allpass Filter 2nd Order: Pure Phase Shift Without Touching the Magnitude Spectrum

Every filter you've used so far in this series attenuates some frequencies. The allpass filter does something different: it leaves the magnitude spectrum completely untouched — 0 dB gain at every freq

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Jeongeun KimApr 18 · 5 min read

Elliptic Lowpass 2nd Order: Maximum Stopband Attenuation at Minimum Filter Order

Elliptic (Cauer) filters achieve the steepest possible transition from passband to stopband for a given filter order. They pay for this with equiripple in both passband and stopband — but when embedde

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Exact RMS, Missed Troughs: A Sampling Trap in Python

Revolutionizing 5G Networks with Intelligent Reconfigurable Surfaces and Deep Reinforcement Learning

Can Your Router Actually See You? The Science of WiFi-Based Human Sensing

State Variable Filter: One Biquad Structure, Three Simultaneous Outputs

Butterworth Lowpass 4th Order: 80 dB/Decade Rolloff With Zero Passband Ripple

High Shelf Biquad: Boost High Frequencies Without Distorting Your Control Bandwidth

FIR Lowpass Kaiser Window: Linear-Phase Precision for Control Signal Filtering

Low Shelf Biquad: DC-Range Gain Shaping Without Integrator Wind-Up

Allpass Filter 2nd Order: Pure Phase Shift Without Touching the Magnitude Spectrum

Elliptic Lowpass 2nd Order: Maximum Stopband Attenuation at Minimum Filter Order