DAMDF(1)

💖 DAMDF(1) 💖

okay so real talk: this is the damdf page from the BRL-CAD manual set, and it's genuinely one of the most straightforward little tools ever. no flags, no drama, no ✨options section✨ — just vibes, doubles, and math. let's get into it 🫶

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✨ NAME ✨

damdf — literally just computes the average magnitude difference function of a stream of doubles. that's it. that's the whole personality 🎀

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🌸 SYNOPSIS 🌸

damdf [window_size] < input.doubles > output.doubles

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🦋 DESCRIPTION 🦋

okay so bestie, here's the whole ~situation~:

damdf reads double-precision floating-point samples in from standard input, computes the Average Magnitude Difference Function (AMDF for short, iykyk) over successive windows, and writes the resulting doubles out to standard output. slay 💅

so what even is an AMDF? it's an experimental measure used for pitch extraction 🔥 and the way it works is genuinely kind of iconic: for each lag, it accumulates the sum of absolute differences between a window and a lag-shifted copy of itself, then it outputs 1024 minus that sum — so that strong periodicities show up as peaks. the math is mathing, periodt 👑

input is processed in fixed blocks of window_size samples (and listen, the default is 512, no cap). a final partial block gets zero-padded to a full window, so nothing's ever left hanging 🙈 each block produces window_size output values.

now for the vibe check that actually matters: because both streams are raw binary doubles, damdf refuses to run if either standard input or standard output is a terminal. it's a hard no lol 💀

and here's the thing — it does not take any option flags. at all. zero. the only argument is the optional positional window_size. that's the entire CLI. minimalist queen 💜

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🎀 EXAMPLES 🎀

Example 1. Estimate pitch periodicity of a sampled signal

damdf 1024 < signal.doubles > amdf.doubles
dpeak < amdf.doubles

so what's happening here: this computes the AMDF of a stream of doubles over 1024-sample windows, then locates the dominant peaks with dpeak(1) 🔍 the lag of the largest peak corresponds to the estimated pitch period. genuinely so satisfying when it works 🌈⭐

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💫 SEE ALSO 💫

• brlcad(1)
• dauto(1)
• dfft(1)
• dpeak(1)
• dmod(1)

go read those next, bestie, they're all in the same friend group 🫶

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👑 AUTHOR 👑

BRL-CAD Team — icons only 💖

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🍓 COPYRIGHT 🍓

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

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😭 BUG REPORTS 😭

Reports of bugs or problems should be submitted via electronic mail to devs@brlcad.org — please don't suffer in silence, fr fr 💀🙈

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okay bestie that's the whole page!! this one ships out under the BRL-CAD banner (that's the source/version at the bottom of the original, BRL-CAD on the left and DAMDF(1) on the right, no date field to worry about!) — and that's a wrap 🌸✨💅