Hosting a VST in APO, getting short volume spike on audio starting, 500ms(?)
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For various reasons I need to host Slate VSX (a room emulation software) on Windows. FYI there is a Slate native host (VSXSystemwide) but I've had so many issues with it I decided to find another way to host the VST.
I've added the VSX VST as the only item in APO, and it works perfectly - with one minor issue.
Everytime I start a new audio input (ie launch Chrome and play a YouTube video or Launch Spotify and play a track) I get a huge initial volume spike. Once the application (eg Spotify) has experienced the spike on first play the issue in that app doesn't reoccur - unless I restart the app, then it happens once again.
The volume spike lasts a fraction of a second (maybe 500ms).
My best guess is that because the VSX plugin applies a gain reduction (since it's applying it's own EQ curves) the initial volume 'spike' is actually the audio playing a split second BEFORE the VST plugin initialises. It's like APO waits until the new app (eg Spotify) initialises audio THEN launches the VST.
I've tried various options including adding a PreAmp gain reduction in front of the VSX plugin but the issue remains.
Any ideas?
FWIW I've just tested some other random VSTs (eg a bitcrusher and a distortion) and they work perfectly.
My guess is that sinc VSX is a large plugin (c.150 MB) that the delay is APO loading it into memory...
Any ideas on how I can eliminate this delay?? Is there an advanced always pre-load VST option somewhere?
Last edit: James Osborne 2025-11-05
Unfortunately there isn't a pre-load VST option. Basically it's about the audio engine (the APO) of Equalizer APO reading and processing the config.txt file. I don't why this doesn't happen immediately. As this engine isn't a process of its own, only after an audio stream is initiated (commonly playing some sound) the engine is able to read the config.txt file and in your case initiate VSX VST. And you're right, that may take some time and it could be that the audio buffer in VSX VST (if any) needs to be filled.
The only possible solution I can think of is to add a delay by adding a delay command before the VST plugin command. Perhaps this prevents the initial volume spike although it could do nothing good as now both, the delay and VST plugin commands need to be processed.
As an update, in case anyone else is also ever trying to troubleshoot this issues. The spike re-occurs if an app has not played audio in a while (maybe 5 mins?) Eg pause a YouTube video and resume after a few mins, loud volume spike.
It actually feels like APO goes into sleep mode when audio is not playing, would be interesting to understand if there's a way to force it to stay active (I'll take this miniscule CPU hit!)
Thanks for the info. Perhaps continuously play some silent sound file or almost silent like 1 bit volume would help. The problem is if the audio stream dries up (no sound is playing) the engine of Equalizer APO can't do anything as its functions aren't called. Note that the engine isn't an app or process. It's all handled by the Windows audio service. So the engine isn't really going into a sleep mode. Its current settings should be all nicely stored in memory. Clearly that isn't the case. Although something entirely else may go on of which we aren't aware of.
soundkeeper
THANK YOU! I was a bit hesitant to have an audio app running 24/7 in the background since I use my PC for audio production (eg ASIO drivers in my DAW etc) however Soundkeeper on default settings just works! I can watch YouTube and listen to Spotify without issues!
Legend!
Just great!
Good call!