wiki:BuildingCarrierWave

Building the Carrier Wave

  • Select a segment to analyze
  • Hit Ctrl-E to zoom into region

  • Continue zooming until the region is clearly visible

  • A careful visual examination reveals that a repeating signal is present
  • Three pairs of two high spikes can be seen
  • In this screenshot the repeating signal is highlighted, consisting pairs of high spikes, grouped into sets of three

  • The first set has been selected in Audacity

  • In order to build the carrier wave start with the longest continuous region of clear, repeating signals
  • Expand the selection from the start of the first set to the start of last set of three pairs

  • Zoom to the maximum level of detail at the start of the selected zone
  • In the following screenshot, the mouse button is being held down (turning the cursor into an arrow)
  • The exact data point is being marked by the cursor
  • Notice the time index at the top of the track editor is in alignment with the mouse cursor and that the "Selection Start" figure at the bottom of the track editor reads "00 h 00 m 33.984 s"
  • This mark is high spike at the start of our signal
  • Notice that the region of the track highlights to the left of the mouse cursor is actually some distance away from the mouse cursor. This behaviour seems somewhat odd, but can be ignored for the moment

  • Zoom and scroll to the end of the selected area
  • Zoom back into the maximum resolution at the end of the selected area, as seen in the following screenshot
  • Notice that once again the mouse button is being held down (turning the cursor into an arrow) over the exact data point which matches the first peak at the beginning of the next set of three pairs
  • Again the time index at the top of the track editor is in alignment with the mouse cursor. The "Select End" figure at the bottom of the track editor reads "00 h 00 m 33.997 s"
  • Audacity has also offset the region of the track highlight to the left of the mouse cursor, the same distance as seen in the previous screenshot.
  • We now have selected a perfectly repeating wave, containing four complete copies of the carrier signal

  • Zoom back out in order to see the entire selected area
  • Click the name of the track at the upper-lefthand corner of the track
  • Select "Split Stereo to Mono" in order to separate the control signal (left channel, on the top) from the carrier wave (right channle, at the bottom)

  • We now have two Mono audio tracks

  • Delete the control signal (on the top) by clicking the "X" marker to the left of the track name
  • Only the carrier signal remains
  • Hit Ctrl-C to copy the selected region

  • Delete the carrier signal track

  • Hit Ctrl-X to paste only the selected region into the track editor

  • Zoom in to see the pasted signal
  • Press Home to "Skip to Start" of the track

  • Press Ctrl-V to past another copy of the signal into the track editor
  • Press Home to return to the start of the track

  • Repeat this process, building a longer and longer track containing the carrier signal

  • By hovering the mouse cursor over the line segments and clicking the left button, the segments can be joined together into a single contiguous track

  • Continue this process until at least one second has been created

  • Copy the entire second and repeat the copy-and-paste procedure until building a carrier signal track of the desired length (in this case 10 seconds)

  • Join all segments until the entire track is complete

Optional: Create a Stereo version of the Carrier Signal

  • Highlight the entire 10-second track and press Ctrl-C to copy it to the clipboard
  • Click in the empty region of the track editor below the completed 10-second track
  • Press Ctrl-V to paste a second copy of the carrier signal
  • Click the track name and select "Make Stereo Track"
  • Export the stereo track to a WAV file

Last modified 6 years ago Last modified on 11/27/12 09:58:41