Audio Processing

Multiple loudness, normalization, mono, change kbit

for f in *.mp3
    # loudnorm and true peak and convert to mono with ffmpeg
    do ffmpeg -i $f -ac 1 -ab 64k  -af loudnorm=I=-16:TP=-1.5:LRA=11 `basename $f .mp3`-MONO-LOUDNORM.mp3
done

ffmpeg -i $f -ac 1 -ab 64k -af loudnorm=I=-16:TP=-1.5:LRA=11 `basename $f .mp3`-MONO-LOUDNORM.mp3

  • -i $f | input file name
  • -ac 1 | Set the number of audio channels. 1 = Mono
  • -ab 64k | Set the audio bitrate in bit/s
  • -af loudnorm=I=-16:TP=-1.5:LRA=11 | Apply EBU R128 loudness normalization. Includes both dynamic and linear normalization modes.

For details regarding the filters, see:

Normalize files

sox --norm output1-MONO.wav output1-MONO.wav

Create WAV with 22kHz

sox GestiefelterKater-01-MONO.wav -r 22050 GestiefelterKater-01-MONO-22kHz.wav

Split long audio files (mp3/ogg)

mp3splt -f -t 4.0 -a -d split *.mp3

Now press the key to start the splitting. Mp3Splt writes status messages in the Command Prompt window as it works.

All the command line options are listed farther below. Here’s an explanation of the recommended options:

  • -f: for MP3 files only, increases precision and is needed if the MP3 files are variable bit rate (VBR).
  • -t TIME: specifies the length, measured in time, to make each piece. You will replace TIME with a numerical value expressed in minutes, such as 4.0 for four minutes or 7.30 for seven minutes, thirty seconds. In our example, we picked four minute pieces, so the command line will be
  • -a: automatically adjusts the split points to occur during silences, which avoids splitting in the middle of a word. Therefore, the pieces will vary in their exact length.
  • -d split: writes the split files to a sub-folder named split(you may pick any name you wish). The folder will be created if it doesn’t already exist. It’s more convenient if you don’t put the split files in the same folder with the original ones.
  • *.mp3: process all the MP3 files in the current folder. If you are splitting Ogg Vorbis files, change this to *.ogg.
mp3splt -a -t 30.00 -o Drood_02-@n -d Drood Drood2-MONO.mp3