ion.ogg: replaced with free variant

LICENSE.md

@@ -29,6 +29,9 @@
     - connect.ogg: Tshhhhed into a microphone, pitch lowered by 15 semitones
     - crash.ogg: Hit a fire extinguisher with a chunk of metal. Changed speed (incl. pitch) to 1/2
     - electricmotor.ogg: A rotating razor without blades, shifted down an octave
+    - ion.ogg: This consists of 2 overlaid parts:
+        - Medium-pitched: A foil razor at slow speed with blades but no foil, shifted down 2 octaves.
+        - Low-pitched, combustion-motor-like: The same foil razor at max speed with blades removed, shifted down 3 octaves, changed speed (incl. pitch) to 1/2. Low-pass filtered at 1khz with 36db roll-off per octave.
     - gasp.ogg: Gasping for air
     - gasprelief.ogg: Heavy breathing
     - growl.ogg: Growled into a Xaphoon (2024-09-13@18:21), lowered by an octave, added reverb
@@ -36,9 +39,6 @@
     - wakeup.ogg: Heavy breathing
     - woosh.ogg: Blew into the mic, pitch lowered by 24 semitones
     - zoom.ogg: Recorded a screw thread scraping against a saxophone ligature
-- Other sound files: [Pixabay Content License](https://pixabay.com/service/license-summary)
-    - https://pixabay.com/sound-effects/electricity-6353
-    - https://pixabay.com/sound-effects/high-energy-humming-195612
 - Music:
     - JupiterRecording.ogg is an [actual Jupiter recording by NASA](https://archive.org/download/voyager-1-and-2-1990-jupiter-nasa-voyager-space-sounds-electronic), public domain.
         - Processed by cutting out min 1:47-3:47 and applying a 10s linear crossfade at the end. Exported as ogg with quality=3, see [.kdenlive file](src/audio/JupiterRecording.kdenlive).