/usr/lib/puredata/doc/3.audio.examples/H06.envelope.follower.pd is in puredata-doc 0.43.0-4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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#X floatatom 354 464 4 0 0 0 - - -;
#X floatatom 150 316 3 0 999 0 - #0-osc2 -;
#X obj 150 336 osc~;
#X text 162 12 ENVELOPE FOLLOWER;
#X text 22 33 An envelope follower measures the mean square power of
an signal as it changes over time. (You can convert mean square power
to RMS ampitude or to decibels if you wish.) The term "mean square"
means simply that the signal should be squared \, and then averaged.
The averageing is done using a low-pass filter such as lop~.;
#X obj 62 466 lop~;
#X floatatom 93 444 3 0 100 0 - #0-lop -;
#X obj 61 356 +~;
#X text 187 317 <-- frequency of second oscillator;
#X obj 62 330 osc~ 500;
#X obj 62 413 *~;
#X obj 62 522 snapshot~;
#X floatatom 62 573 5 0 999 0 - - -;
#X obj 62 545 sqrt;
#X text 335 361 built-in envelope;
#X obj 354 491 dbtorms;
#X floatatom 354 518 5 0 999 0 - - -;
#N canvas 536 459 382 265 startup 0;
#X obj 22 24 loadbang;
#X obj 22 48 bng 15 250 50 0 empty empty empty 0 -6 0 8 -262144 -1
-1;
#X obj 22 67 f \$0;
#X text 35 195 This subpatch loads initial;
#X text 31 219 values in number boxes.;
#X msg 22 91 \; \$1-osc2 400 \; \$1-lop 10 \; \$1-metro 1 \; pd dsp
1;
#X obj 223 132 metro 250;
#X obj 223 107 r \$0-metro;
#X obj 223 156 s \$0-tick;
#X connect 0 0 1 0;
#X connect 1 0 2 0;
#X connect 2 0 5 0;
#X connect 6 0 8 0;
#X connect 7 0 6 0;
#X restore 217 598 pd startup;
#X text 115 414 square the signal;
#X text 124 440 <-- responsiveness;
#X text 159 501 take snapshot;
#X text 108 548 convert to RMS;
#X text 327 599 updated for Pd version 0.39;
#X text 334 381 follower for comparison;
#X text 107 466 low-pass filter;
#X text 114 573 output;
#X obj 70 497 r \$0-tick;
#X text 159 517 every 1/4 second;
#X obj 389 439 r \$0-tick;
#X obj 354 439 f;
#X obj 376 414 env~;
#X text 20 242 The env~ object at right \, which is a built-in envelope
follower using a higher-quality low-pass filter than lop~ \, is shown
for comparison. Its output is artificially slowed down to match the
homemade one at left.;
#X obj 150 359 *~;
#X obj 185 360 tgl 15 0 empty empty empty 0 -6 0 8 -262144 -1 -1 0
1;
#X text 204 358 <-- on/off;
#X text 20 128 Here we're adding two oscillators so the result should
be an RMS of one if the second oscillator is on \, 0.707 otherwise.
Note two effects: first \, the more responsive the envelope follower
\, the less accurate the result (but the faster it responds). Second
\, if the two oscillators are tuned close to each other their beating
affects the nombers coming out.;
#X connect 0 0 15 0;
#X connect 1 0 2 0;
#X connect 2 0 32 0;
#X connect 5 0 11 0;
#X connect 6 0 5 1;
#X connect 7 0 10 0;
#X connect 7 0 10 1;
#X connect 7 0 30 0;
#X connect 9 0 7 0;
#X connect 10 0 5 0;
#X connect 11 0 13 0;
#X connect 13 0 12 0;
#X connect 15 0 16 0;
#X connect 26 0 11 0;
#X connect 28 0 29 0;
#X connect 29 0 0 0;
#X connect 30 0 29 1;
#X connect 32 0 7 1;
#X connect 33 0 32 1;
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