Audio Enhancement for 27 Math YouTube Videos

I have 27 Math YouTube videos, each around 1-hour long, that require audio improvement. The project involves downloading the videos in HD, extracting the audio, and using Audacity to remove background noise, specifically AC and fan noise. Additionally, the audio needs to be enhanced through volume normalization, echo reduction, and leveling out voice pitch. In your proposal, put "HD27Now". The final output should be delivered as a high-quality link to download or through HD YouTube playlist where the fixed videos can be re-downloaded.