Audio & Signal Notes

Audio & signal processing, and the music-production numbers beside it

Every article walks through the maths behind a measurement, the traps that come with it, and then hands you a calculator that does the work in your browser. Signal processing and DSP on one side; tempo, pitch and delivery level on the other. Nothing is uploaded, nothing is stored, no account is needed.

Browse the tools Music calculators Read the articles

Core articles

Each entry below is a full tutorial page with a working tool built into the body of the text — not a bare calculator page. Publication order follows the schedule in the article index.

Extended series

Follow-ups that take one subject further, where the practical question turns out to be subtler than the theory.

  • Published

    THD, THD+N, SINAD and ENOB

    Measure distortion from a captured tone, with the definitions, the bandwidth caveat, and the harmonic arithmetic people get wrong.

  • Published

    Biquad Coefficients (RBJ Cookbook)

    Peaking, shelving, low-pass, high-pass, band-pass, notch and all-pass coefficients with the response and group delay measured from them.

  • Published

    Speaker SPL & Amplifier Power

    Sensitivity in either convention, level against distance, air absorption, cabinet stacking and the power a target level really needs.

  • Published

    Level Summation Calculator

    Add correlated and uncorrelated levels, stack identical sources, remove a noise floor, and average levels over time.

  • Published

    Loudness & True Peak Analyser

    Integrated LUFS with the gating shown block by block, loudness range, and true peak against the sample peak.

  • Published

    A, C and Z Weighting, and What Leq Averages

    The weighting curves from their poles, why a meter reads 30 dB low at 50 Hz, and how an equivalent level averages energy rather than level.

  • Published

    Room Mode Calculator

    Mode spectrum with coincidences flagged, mode count against the asymptotic curve, and the pressure shape of any mode.

  • Published

    RT60: Sabine, Eyring and Where the Formula Fails

    Reverberation time computed both ways, the absorption a target needs, and the point where Sabine over-predicts by a factor of two.

  • Published

    SBIR: Boundary Interference and Speaker Placement

    Path difference from the front and side walls, the first null each one causes, and why 2d is right for one of them and wrong for the other.

  • Published

    Loudspeaker impedance, reflection and return loss

    Why the number on the cabinet is a convention, what the reflection coefficient costs you, and the DCR tolerance test that catches a dead driver.

  • Published

    Speaker Cable: Resistance, Damping Factor and Loss

    Loop resistance from length and gauge, the damping factor that follows from it, and the point where thicker cable stops changing anything.

  • Published

    Closed-Box Alignment: Qtc, Volume and the -3 dB Point

    Size a sealed box from Vas and Qts, see what each Qtc value sounds like, and why Fc coincides with f3 only at Butterworth.

  • Published

    Passive Crossover Calculator

    Butterworth and Linkwitz-Riley ladders, with the response measured off the component values.

  • Published

    Subwoofer Time Alignment

    Why the distance formula is not enough: what delay, distance and polarity each correct, and the crossover delay that outweighs the geometry.

  • Published

    Band-pass Level Loss

    Two filters in series multiply, so a band-passed driver cannot reach full output. The closed form for how much, and what correcting it costs in headroom.

Music production

The everyday units of playing and producing: tempo, pitch and delivery level. Same approach as the rest of the site — the ratio behind the number, and a tool that runs in your browser. The three are collected on the music calculators page.

  • Published

    BPM to ms Calculator

    Every note value, dotted and triplet, with the reverse lookup and a tap tempo that ignores a fumbled tap.

  • Published

    Cents & Tuning Calculator

    How far off a pitch is in cents, what your A4 means, and where the reference has moved over the centuries.

  • Published

    LUFS Normalisation Calculator

    The gain that hits a delivery target, and whether the true peak still fits under the ceiling afterwards.

Supporting calculators

Smaller utilities that cover the checks you make in passing: CRCs, sampling limits and acoustic timing.

  • Published

    CRC-8/16/32 Calculator

    All the standard parameter sets with their catalogue check values, plus custom polynomial, init, reflection and final XOR.

  • Published

    Nyquist & Aliasing Calculator

    Where an out-of-band tone folds to, the samples per cycle, what oversampling is worth, and the jitter-limited SNR.

  • Published

    Acoustic Time & Distance Calculator

    Delay, distance and temperature-dependent speed of sound, with the sensitivity that decides whether the answer matters.

  • Published

    Audio File Size Calculator

    Size from sample rate, bit depth, channels and duration, how many hours a gigabyte holds, and why 24-bit is not twice 16-bit.

How these tools are built

All arithmetic runs client-side in JavaScript, with the numerically heavy parts (FFT, coherence, RMS accumulation) moving to WebAssembly as the site grows. That choice is deliberate: your measurements never leave the machine, and the page keeps working offline once loaded.

Results are shown with significant digits chosen for the magnitude involved, because pasting a raw double into a report is how rounding errors get published. Where a quantity is only valid under a stated assumption — a reference level, a window, an averaging count — the article says so and the tool says so.

A tool has no way to send anything anywhere even if it wanted to: there is no analytics, no tracking pixel and no account, and what you type never leaves the page. The one third party on the site is Google's advertising code, which appears on article pages only and never inside a calculator; the privacy policy sets out exactly what it does.