DFFT(1)

📦 version 7.44.0, in nixpkgs unstable

💖 DFFT(1) — the dfft page, but make it cute 💖

okay so bestie, welcome to the BRL-CAD manual, section 1, and today's main character is dfft 🎀

✨ NAME ✨

dfft — computes fast Fourier transforms of a stream of doubles 🦋

🌸 SYNOPSIS 🌸

dfft [-clpLAN] [-d dB] [width] < doubles > spectrum

💅 DESCRIPTION 💅

okay so here's the vibe: dfft reads a stream of double-precision floating-point samples from standard input, computes the real fast Fourier transform of each 1024-sample record, and writes the resulting spectrum to standard output. literally that's it and it ate 🔥

⚠️ and like, both standard input and standard output must be redirected, no cap. If either one is a terminal, dfft prints a usage message and exits. it's giving "not today" 💀

by default the output is the periodogram-scaled log-magnitude in decibels, written as 512 double-precision values per 1024-sample record. iconic ✨

the options let you pick, like, a whole different era:

  • phase output instead of magnitude 🌙
  • a linear (non-dB) magnitude scale 📏
  • a logarithmic frequency scale 📈
  • a third-octave critical band filter 🎚️
  • normalization to the peak magnitude 👑
  • or human-readable ASCII text 🫶

the optional width argument? she's accepted for historical compatibility but ignored, periodt. the transform length is fixed at 1024 samples, yielding 512 output values. that's the law 💅

input is normally produced by a tool such as dconv(1) or dmod(1) — iykyk 🧚

✨ OPTIONS ✨

  • -d dB — set the minimum magnitude in decibels. you give it a positive value and it gets applied as its negative, ok? magnitudes below this floor are clamped when the output is normalized. default is 120, i.e. -120 dB 🙈
  • -l — interpolate the magnitudes onto a logarithmic frequency scale 📈
  • -c — apply a third-octave critical band filter to the magnitudes 🎚️
  • -p — output the phase, in units of pi, instead of the magnitude 🌙
  • -N — normalize the power spectral density so the peak is 0 dB (or 1.0 in linear mode) 👑
  • -L — output linear magnitude rather than log-magnitude in decibels 📏
  • -A — write human-readable ASCII text instead of binary doubles. each line holds a frequency fraction and its magnitude separated by a space 📝
  • -h, -? — print a usage message and exit 🫶

🦋 EXAMPLES 🦋

Example 1. Plot a power spectrum

dfft -A -N < signal.doubles > spectrum.txt

computes the FFT of the samples in signal.doubles, normalizes the power spectral density to a 0 dB peak, and writes (frequency, magnitude) pairs as ASCII text suitable for feeding to a plotting program. plot girl summer 🌸✨

Example 2. Critical band magnitude on a log frequency scale

dmod -m 32768 < raw.doubles | dfft -c -l > bands.doubles

scales the raw samples with dmod(1), then computes a third-octave critical-band-filtered spectrum interpolated onto a logarithmic frequency scale, producing binary doubles for further processing. pipeline? slayed 💅🔥

🌈 SEE ALSO 🌈

brlcad(1), dconv(1), dmod(1), dauto(1), dwin(1), dstats(1)

👑 AUTHOR 👑

BRL-CAD Team 💜

This software is Copyright (c) 1989-2026 by the United States Government as represented by U.S. Army Research Laboratory.

💀 BUG REPORTS 💀

Reports of bugs or problems should be submitted via electronic mail to devs@brlcad.org 📧 — like, please actually tell them, don't just suffer in silence bestie 😭

okay that's the whole page!! from the BRL-CAD girlies, DFFT(1), dated 2026, mwah 💋 send your bug mail, stay hydrated, and remember: redirect your stdin AND your stdout 🫶💖

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