title: Record N samples to file following rising edge trigger
body: <p>Given a stream of float values how do I record a given number of samples to a file following a rising edge trigger with a set threshold?</p>
  <p>I'm looking at Burst tagger, Tagged file sink but cannot figure out how to keep the tag set for a given timeout after the initial rising edge.</p>
  <p>Also looked at Trigger rising edge even but cannot figure out how to make it register the events and then use the event to start recording with a timeout (trying to output edge_event into a Message Debug block, but it's not printing anything).</p>