I used some complex filters on a audio file and did some re-encoding.
ffmpeg -f lavfi -t 5 -i anullsrc=channel_layout=stereo:sample_rate=192000 -i file1.mp3 -filter_complex "[1:a][0:a]concat=n=2:v=0:a=1[audio_silence],amovie=file2.mp3:loop=0,asetpts=N/SR/TB,volume=0.1[music];[audio_silence][music]amix=duration=shortest,volume=1" out.mp3
Everytime I do this the audio gets worse. The audio is some speech recording and there are a lot of hisses and high frequency noices in the output. How can this be prevented or equalized afterwards? I tried some low pass filters but that doesn't seem to work.