poll

functions

example

-- !! polls should always be established within a script's 'init'!!

function init()

  last_pitch = 0
  last_amp = 0

  pitch_tracker = poll.set("pitch_in_l") -- create a poll to detect pitch of the left input
  pitch_tracker.callback = function(x)
    if x > 0 then -- poll returns `-1` without a signal present
      last_pitch = x
      screen_dirty = true
    end
  end

  amplitude_tracker = poll.set("amp_in_l") -- create a poll to detect amplitude of the left input
  amplitude_tracker.callback = function(x)
    if x > last_amp then
      last_amp = x
    elseif util.round(x,0.0001) == 0 then
      last_amp = 0
    end
    screen_dirty = true
  end
  amplitude_tracker:start() -- automatically poll amplitude

  screen_timer = clock.run(
    function()
      while true do
        clock.sleep(1/15)
        if screen_dirty then
          redraw()
          screen_dirty = false
        end
      end
    end
  )

end

function key(n,z)
  if n == 2 and z == 1 then
    pitch_tracker:update() -- manually poll pitch
  end
end

function redraw()
  screen.clear()
  screen.level(15)
  screen.move(0,20)
  screen.text("press K2 to sample pitch")
  screen.move(0,30)
  screen.text("incoming pitch: "..string.format("%.2f",last_pitch).." Hz")
  screen.move(0,50)
  screen.text("incoming amplitude: "..string.format("%.2f",last_amp*100).."%")
  screen.update()
end

description

Polls report basic data from the audio subsystem, for use within a script. Trigger script events based on incoming amplitude, or capture the pitch and match it with a synth engine. See study 5 for additional examples.

Here are the pre-built polls, made available by the norns system:

• amp_in_l: returns the amplitude of the incoming signal as a percentage of the largest amplitude that can be captured before clipping
• amp_in_r
• amp_out_l: returns the amplitude of the outgoing signal (output from a loaded engine, not softcut, monitor, or the general norns output level) as a percentage of the largest amplitude that can be captured before clipping
• amp_out_r
• cpu_avg
• cpu_peak
• pitch_in_l: returns pitch value in Hz
• pitch_in_r

writing your own polls

Writing your own polls is an incredibly useful technique for reporting information from a SuperCollider engine back to the Lua scripting layer.

Polls can be declared in an engine file using this.addPoll, eg.

this.addPoll(\outputAmpL, {
	// 'getSynchronous' lets us query a SuperCollider variable from Lua
	var ampL = kernel.amplitude[0].getSynchronous;
	ampL
});

The above relies on a bit of coordination, so let’s rewrite the amp_in_l and amp_in_r polls, but with additional control over each channel’s gain:

• lib/ExamplePoll.sc: a Class file which uses SuperCollider’s Amplitude.kr UGen to track the incoming amplitude of both channels
• lib/Engine_ExamplePoll.sc: wraps the ExamplePoll.sc Class file into the norns engine template, adding polls for each channel to report their amplitude back to the Lua scripting layer
• poll-example.lua: initializes our polls and represents the incoming amplitude data as two independent circles on the screen

(download all files as a zip – be sure to restart norns after!)