My soruce is an old vhs-tape with very low audio level, so I normalized it to hear the speaking persons better, but now I have terrible audio noise. is there an audio-filter to remove the noise?
Never done this in Kdenlive, but I assume there is an effect for this, just check the audio effects list.
If not, you might want to try running the audio through Audacity, I know their noise removal filter is quite good. You could then join the audio and video back up in Kdenlive
You can't, moorsey didn't mean it that way, just extract your audio from the video to an uncompressed format, run it through Audacity, and drop it back into kdenlive as a second audio track?
sorry I don't quite follow you, currently do you use kdenlive to extract audio from the edit? It's simple to do the audio extract from the source video files with ffmpeg or similar on the CLI or batch script outside of kdenlive, process that in Audacity and then import the 'cleaned' audio into kdenlive complete as a source clip, to sync with the unedited video stream?
But have you also investigated the LADSPA plugins, there may well be suitable filters already available within kdenlive to do the job.