Unfortunately, the majority of technical details on the web on implementing VU meters in the digital domain is misleading, of not outright wrong. A while back,

Unfortunately, the majority of technical details on the web on implementing VU meters in the digital domain is misleading, of not outright wrong. A while back, I implemented VU meters for some professional AV software. I started with the available references, but quickly discovered that it was well-intentioned but incorrect/inaccurate. I ended up sourcing the original specification for the analog meters, and then devising digital filters to replicate the same ballistics. This matched perfectly with the reference, (pro hardware). TL;DR don't believe what you read on the web. Go to primary sources!