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Classic Minecraft Mod Sound Sources
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Research by PessiMysterio and IcarussOne
Thaumcraft sounds researched for Sonomagy
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This spreadsheet lists the original sound effects used in many classic Minecraft mods, most notably for Thaumcraft 1-6 (as these sounds have been used for the Sonomagy soundpack) but also for other mods too. Is there a classic Minecraft mod you always liked the sounds for? Well there's a good chance the creator googled "free soud effecx" and clicked on the first search result back in 2012. Either that or they made weird noises into their laptop microphone.

Do keep in mind that this spreadsheet was made simply to document how old mods did their sound design for anyone curious about the topic. Please don't treat this as a callout or as drama - we're here because we enjoy Minecraft and its mods.

Research is broken up into several sub-sheets and named appropriately; check the tabs below to select one of these and have a look.

Feel free to use this list as a reference, and if you find any sound sources of your own then go ahead and contact me; I can be found at the link to the Sonomagy soundpack above or contacted on Discord: "PessiMysterio"/"pessimysterio".
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Want information on vanilla Minecraft's audio? For music, the Newer VGM Sound Sources spreadsheet is the place to go - use ctrl-F to search for "Minecraft".
For sound effects, The Minecraft Sounds Sources Spreadsheet covers that in a LOT more detail.