FL Studio (formerly Fruity Loops) is highly unpredictable when it comes to blocksize handling. All our plug-ins highly depend on static blocksize due to the high amount of complex calculations.
We encountered a similar issue and found the following workaround in FL12:
frei:raum ist actually also VST3 – it’s simply not copied to the respective folder.
- pick the VST freiraum.dll (probably from C:\Program Files\Steinberg\VSTPlugins) and MOVE it to C:\Program Files\Common Files\VST3
- rename it to freiraum.vst3
- open FL and load an instance of frei:raum – the user interface will open (please do NOT start playback)
- click the "Settings" icon in the top-left corner
- switch to the "Processing" tab
- tick the “Used fixed size buffer” checkbox
- audio should start to flow now
Please also make sure that the overall buffersize is at least 1024 samples!
Additionally, there’s also a fix from Image-Line taken from their forum:
1. Open FL Studio.
2. Refer to the "Plug-in Database" > "Effects" folder of your FL Studio Browser.
3. Locate and delete any frei:raum entries saved in this location by right-clicking the entry and selecting "Delete file" If you don’t have a favorite entry for frei:raum you can proceed.
4. Download, extract, and launch the attached freiraum.reg file. (http://downloads01.sonible.com/download.php?file=misc/freiraum-FL12-fix.zip)
5. Accept any prompts regarding applying the registry key and values.
6. Restart FL Studio once the keys and values are applied.
7. Navigate to ‘Plug-in Database > Installed > Effects > VST’ and load the frei:raum plug-in entry from this location. Test the plug-in.
For those concerned about what the registry file does, it adds a key for frei:raum under HKEY_CURRENT_USER\SOFTWARE\Image-Line\Shared\Plugins\Fruity Wrapper\Plugins\VST with some pre-defined wrapper settings for the plug-in, in particular ‘Use fixed size buffers’ is enabled.