Remove/reduce background noise and hiss from an audio file
This is a two-step process; although, it can be run as a pipeline. First you need to analyze the audio to build up a profile of the noise. You want to sample a range that features only the background noise you want to remove. Typically you can sample the first 1 second of an audio file. This doesn't always work, but it mostly works.
sox audio_recording.wav -n trim 0 1 noiseprof | play audio_recording.wav noisered - 0.2
Trim silent gaps from audio
This removes silent sections from the beginning, middle, and end. Useful for compressing long auidio logs that may contain many long pauses.
sox audio_recording.wav silence_removed.wav silence 1 0.1 1% -1 0.5 1%
Create a spectrogram of an audio file
The rate 6k option will narrow the frequency range view to the band most sensitive for human hearing. This cuts off frequencies above 3 kHz (half the sample rate of 6k). If you want the full frequency range then leave off the rate 6k option.
The -n is the NULL file option. This simply tells Sox that we don't want to actually create a new sound file. We are just analyzing the input file.
sox audio_recording.wav -n rate 6k spectrogram -t "Spectrogram of audio_recording.wav" -o spectrogram_20150531.png # For a white background use '-l' option: sox audio_recording.wav -n rate 6k spectrogram -l -t "Spectrogram of audio_recording.wav" -o spectrogram_20150531.png
Record audio from the microphone
arecord -vv -fdat recording.wav
Using Sox (this works on OS X). This splits on silent gaps:
rec -r 44100 -b 16 -s -p silence 1 0.50 0.1% 1 10:00 0.1% \ | sox -p audio_recording.wav silence 1 0.50 0.1% 1 2.0 0.1% : newfile : restart
Playback audio OX X using Sox
Note that where an output filename is require you may substitute -d or -t coreaudio (for Mac OS X). These seem to be equivalent. The -d option seems to be the more general purpose style since it will automatically pick the correct sound output on a Mac and Linux.
Both examples below play audio and both will automatically detect the audio stream type. The play command is the easier to remember version. You may have special reasons for wanting to use the sox command alternative.
play audio_recording.wav cat audio_recording.wav | sox - -t coreaudio
These are all equivalent using /dev/urandom.
# From a file or device file. sox -t raw -r 44100 -b 16 -e unsigned-integer /dev/urandom -d sox -t raw -r 44100 -b 16 -e unsigned-integer /dev/urandom -t coreaudio # Using a pipe... cat /dev/urandom | sox -t raw -r 44100 -b 16 -e unsigned-integer - -d cat /dev/urandom | sox -t raw -r 44100 -b 16 -e unsigned-integer - -t coreaudio
This uses Sox's built-in noise generator:
play -n synth whitenoise