Rain audio for Shelter FM

Author: Ove Melaa
Source page: https://opengameart.org/content/rain-ambient-not-loopable-2-versions-available
Original file: Ove Melaa - Rainy (NOT loopable).ogg (short version)
Download: https://opengameart.org/sites/default/files/Ove%20Melaa%20-%20Rainy%20%28NOT%20loopable%29.ogg
License: CC0 1.0 Universal — https://creativecommons.org/publicdomain/zero/1.0/
The author says attribution is not required. Credit is retained here and in /credits.html.

Preparation: decode to 44.1kHz stereo PCM, take seconds 8–48, move the first
four seconds to an equal-power crossfade with the last four seconds, and encode
at 96kbps MP3. The result is a 36-second loop. Playback raises the naturally
quiet recording by 8dB before the atmosphere, master, and playback-fade gains.

Reproduce with FFmpeg after saving the original file as rain-source.ogg:

ffmpeg -i rain-source.ogg -ar 44100 -ac 2 -c:a pcm_s16le rain-source.wav
ffmpeg -i rain-source.wav -filter_complex '[0:a]atrim=start=8:end=48,asetpts=PTS-STARTPTS,asplit=3[mid][tail][head];[mid]atrim=start=4:end=36,asetpts=PTS-STARTPTS[midcut];[tail]atrim=start=36:end=40,asetpts=PTS-STARTPTS[tailcut];[head]atrim=start=0:end=4,asetpts=PTS-STARTPTS[headcut];[tailcut][headcut]acrossfade=d=4:c1=qsin:c2=qsin[seam];[midcut][seam]concat=n=2:v=0:a=1[out]' -map '[out]' -c:a libmp3lame -b:a 96k -map_metadata -1 rain.mp3

Midnight Train — train.mp3
Source: Background Rumble Noise by gryc
https://opengameart.org/content/background-rumble-noise
https://opengameart.org/sites/default/files/background_ambience.ogg
License: Creative Commons Attribution 3.0 Unported
https://creativecommons.org/licenses/by/3.0/
Attribution and license are linked in credits.html.
Preparation: trim seconds 4–25, resample to 44.1 kHz stereo; arrange the
middle 2–19 seconds followed by a two-second equal-power (qsin) crossfade
of the last two and first two seconds. Encode as 96 kbps MP3 (19 seconds).
Playback level: -12 dB before the Atmosphere slider.

Forest Cabin — forest.mp3
Source: Park ambiences, park_ambience_birds.wav, by Thimras
https://opengameart.org/content/park-ambiences
https://opengameart.org/sites/default/files/park_ambience_birds.wav
License: CC0 1.0 Universal
https://creativecommons.org/publicdomain/zero/1.0/
Preparation: trim seconds 20–60, resample to 44.1 kHz stereo, raise level
by 16 dB; arrange the middle 4–36 seconds followed by a four-second
equal-power (qsin) crossfade of the last four and first four seconds.
Encode as 96 kbps MP3 (36 seconds). Playback level: 0 dB before the slider.