I have a selection of video lectures with different problems in the audio that I would like to clean up, at least to make them bearable to listen to. I have had a go with audacity but would really appreciate some help from an expert. The full audio is at
a) There is an intermittent buzz at the beginning. I have no idea how to remove that.
b) Towards the end (the last 20 minutes) the background hiss gets very loud. I tried the built in noise reduction with the default settings but it wasn’t great.
c) Maybe some others
Any help hugely appreciated.
Raphael
P.S. This is an entirely non commercial enterprise for video lectures at my University.
I don’t think you will get many volunteers to download, or attempt cleaning several hundred megabytes - you are more likely to get a response if you post a couple of 30 second clips. (mono files will reduce the size by 50%).
The audio that you are starting with is very poor, so there are severe limits on what you will be able to achieve,
I would start by normalizing (to get the volume level up and remove any DC offset), then remove a lot of low frequency noise with a high pass filter set at around 250 Hz.
The hum is caused by mains hum (probably due to a bad earth connection on the microphone) and it contains lots of harmonics, so you will only be able to make a little improvement. A notch filter set at 50 Hz, then repeated at 100 Hz and again at 150 Hz will remove some of that buzz, but many of the higher harmonics will remain.
You also need to reduce those loud pops. This will probably need to be done manually by zooming in close on the pops, selecting just to pop, and amplifying by about -20 dB (very time consuming).
When you have done all that, normalise again to say -1 dB
