Sound In

One simple (and perhaps familiar) way of accessing sound inputs is using our friend synth by specifying the :sound_in synth:

synth :sound_in

This will operate just like any synth such as synth :dsaw with the exception that the audio generated will be read directly from the first input of your system’s sound card. On laptops, this is typically the built-in microphone, but if you have an external sound card, you can plug any audio input to the first input.

Duración

One thing you might notice is that just like synth :dsaw the :sound_in synth only lasts for 1 beat as it has a standard envelope. If you’d like to keep it open for a little longer, change the ADSR envelope settings. For example the following will keep the synth open for 8 beats before closing the connection:

synth :sound_in, sustain: 8

Añadiendo efectos FX

Of course, just like any normal synth, you can easily layer on effects with the FX block:

with_fx :reverb do
  with_fx :distortion do
    synth :sound_in, sustain: 8
  end
end

If you have plugged in a guitar to your first input, you should be able to hear it with distortion and reverb until the synth terminates as expected.

You are free to use the :sound_in synth as many times as you like concurrently (just like you would do with any normal synth). For example, the following will play two :sound_in synths at the same time - one through distortion and one through reverb:

with_fx :distortion do
  synth :sound_in, sustain: 8
end
with_fx :reverb do  
  synth :sound_in, sustain: 8
end

Cadenas Múltiples

You can select which audio input you want to play with the input: opt. You can also specify a stereo input (two consecutive inputs) using the :sound_in_stereo synth. For example, if you have a sound card with at least three inputs, you can treat the first two as a stereo stream and add distortion and the third as a mono stream and add reverb with the following code:

with_fx :distortion do
  synth :sound_in_stereo, sustain: 8, input: 1
end
with_fx :reverb do  
  synth :sound_in, sustain: 8, input: 3
end

Problemas potenciales

However, although this is a useful technique, there are a couple of limitations to this approach. Firstly, it only works for a specific duration (due to it having an ADSR envelope) and secondly, there’s no way to switch the FX around once the synth has been triggered. Both of these things are typical requests when working with external audio feeds such as microphones, guitars and external synthesisers. We’ll therefore take a look at Sonic Pi’s solution to the problem of manipulating a (potentially) infinite stream of live audio input: live_audio.