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SoX - Sound eXchange

waterfall diagram

sox bike.ogg -n spectrogram -o bike-spectrogramm.png

Record the output of an soundcard

The idea is to get an audio stream which can be used for diffrent things e.g. streaming or saving as file. ALSA have a file plugin but the following way is nicer.

At first, load the driver as root:

modprobe snd-aloop

Now your soundcard list have a new entry. Based on a host with one soundcard numbered as 0 the loopdevice is 1.

Create a file called .asoundrc in your home directory:

pcm.!default {
  type plug
  slave {
    pcm {
      type asym
      playback.pcm "hw:Loopback,0,0"
      capture.pcm "hw:Loopback,1,0"

You can found the output of hw:Loopback,0,0 as output on hw:Loopback,1,0 as input. You default device is the loopback device because the line pcm.!default.

Not all programs works fine, but this works fine with an one second delay and a lot of traffic.

ssh user@remote_host "rec -t ogg -p" | play -p

At this time, the sound output of a program tunnels through your local host.

The tool ssh connects the remote_host and starts he tool rec -t ogg -p. The rec tool records all sound from the default device which is now the loopback device. The remote sound is put into the ssh tunnel and piped to local play.

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