First figure out what current vendors does. Open terminal and do this to find out which AUs declare themselves as sandbox (un)safe.

find /Library/Audio/Plug-Ins/Components -name "Info.plist" -exec grep -sl sandboxSafe {} \; | xargs -I {} /usr/libexec/PlistBuddy -c 'Print :AudioComponents:0:sandboxSafe' {} > 2.tx

paste 1.txt 2.txt | sort > sandboxsafe.txt

find /Library/Audio/Plug-Ins/Components -name "Info.plist" -exec grep -sl sandboxSafe {} \; > 1.txt                                                                                  

And which one uses resourceUsage tag:

find /Library/Audio/Plug-Ins/Components -name "Info.plist" -exec grep -sl resourceUsage {} \; > 3.txt

find /Library/Audio/Plug-Ins/Components -name "Info.plist" -exec grep -sl resourceUsage {} \; | xargs -I {} /usr/libexec/PlistBuddy -c 'Print :AudioComponents:0:resourceUsage' {} > 4.txt

paste 3.txt 4.txt | sort -f > resourceUsage.txt

In my installed plugins I found out some interesting points:

• MHThumb declares itself as sandbox unsafe and uses resourceUsage tag – GarageBand doesn’t require lowering the security settings.
• Youlean Loudness meter declares itself as sandbox safe and uses resourceUsage tag – GarageBand doesn’t require lowering the security settings.
• SoundToys doesn’t use either option – GarageBand requires lowering the security settings.
• Melodyne uses just resourceUsage tag – GarageBand requires lowering the security settings.
• Replika XT just declares itself as sandbox unsafe – GarageBand requires lowering the security settings.

PS: To reset GarageBand security settings open a terminal and paste:

defaults delete com.apple.audio.SandboxHelper app.com.apple.garageband10

Tom. Developer and Musician. The man behind Virtual Analogy and its products.