Caution
Playing around with audio files. Mainly PCM (Pulse Code Modulation) files, which are just raw audio bytes (samples).
In my simple imagination, they are just a list of bytes, representing samples (for mono audio).
PCM files need metadata to be useful, i.e., Encoding (signed/unsigned, 8/16/etc bits), byte order (big/little endian), channels, sample rate (e.g., 44 kHz).
You can use FFmpeg with the format/encoding "s16le" (signed-16bit-littleendian):
ffmpeg -i in.mp3 -y -f s16le -c:a:1 pcm_s16le out.pcmTo list format/codecs, use
ffmpeg -formats | grep "PCM"
ffmpeg -codecs | grep "PCM"Using lame,
The following command writes an mp3 file with:
- 44.1khz sampling
- 2 bytes (16 bit) per sample
- little endian bit order
- mono audio mode
lame -r -s 44.1 --bitwidth 16 --little-endian -m m out.pcmHere begin the experiments. I mainly use Lua to screw with the raw audio data. Here are some examples. See the rest in the filesystem
| file | what it does |
|---|---|
bitrate_halfer.lua |
This halves the audio bitrate. The way I do it is reading the file, and only writing every other byte to the output. |
volume_doubler.lua |
This doubles the audio volume. The way I do it is reading the file, and writing each byte with value * 2. They will be truncated if they start too loud (i.e., half max volume). |
signal_averager.lua |
This takes a rolling median of the audio signal. It mainly makes things sound super muffled |
To do the whole process at once (screw with audio and turn into mp3), you can use a command similar to this:
cat out.pcm | lua signal_averager.lua │ lame -r -s 44.1 --bitwidth 16 --little-endian -m m "-" out_modified.mp3There is no reason the file has to start life as an audio file. For example, what does this GitHub page sound like?
curl https://github.com/alifeee/audio-experiments | lua signal_averager.lua 50 | lame -r -s 44.1 --bitwidth 16 --little-endian -m m "-" github.mp3We can play with the sample rate and bit width to make it sounds more "underwater-y":
curl https://github.com/alifeee/audio-experiments | lua signal_averager.lua 50 | lame -r -s 1 --bitwidth 8 --little-endian -m m "-" github.mp3or "machine-gun-y":
curl https://github.com/alifeee/audio-experiments | lame -r -s 15 --bitwidth 8 --little-endian -m m "-" github.mp3What does this README sound like?
curl https://raw.githubusercontent.com/alifeee/audio-experiments/main/README.md | lua signal_averager.lua 50 | lame -r -s 1 --bitwidth 8 --little-endian -m m "-" readme.mp3Truly the possibilities are endless.