Stretching Vegas audio with Sound Forge

by Craig Anderton

Figure 1

Sound Forge software is editing an audio file, imported from Vegas Pro software, in order to stretch it. This way, it can match video that has been sped up or slowed down.

The velocity envelope tool in Sony Vegas Pro software is great for "stretching" (shortening or lengthening) a video clip, but the audio doesn't stretch along with it. However, if you have Sony Sound Forge software, you can stretch the audio (within a reasonable amount, like plus or minus 10%) so that it fits the video perfectly. This takes advantage of the fact that you can open up a Vegas Pro file directly in Sound Forge software, edit it, and save it back into Vegas Pro software. Here's how.

  1. Right-click on the Vegas Pro timeline and choose Time for the ruler units. Turn off looping to make sure you don't snap to a loop boundary accidentally in subsequent steps.
  2. Click on the right edge of the video/audio clip (they should be the same length until you speed up or slow down the video), and note the length in the Time Display. We'll assume for this example it's 04:04.144; write this down as the "initial time."
  3. Right-click on the video clip, and go Insert/Remove Envelope > Velocity. Adjust the velocity envelope for the desired amount of stretching. In this case, we'll set it to 90% to lengthen the file somewhat.
  4. "Roll out" the right edge of the video clip until it snaps to its new length. (For example, as we slowed down the velocity, the clip is now longer; you'll need to roll it out to the right.) When the video hits the new snap point, click on the snap point (i.e., the right edge of the video clip) to see the new length - in this case, the Time Display shows 04:30.104. Write this down as the "final time."
  5. Right-click on the audio track, and select "Open Copy in Sound Forge."
  6. Once it's open in Sound Forge, select the entire waveform. (The next six steps all occur in Sound Forge.)
  7. Go Process > Time Stretch. In the Initial Time field, enter the initial time value you wrote down (e.g., 04:04.144).
  8. In the Final Time field, enter the final time value you wrote down (e.g., 04:30.104). Don't worry if this value changes in the steps ahead, Sound Forge will remember these settings as soon as you click on something else (which you'll do next by clicking on Preview).
  9. Click on Preview and audition different stretching Modes. Choose whichever one sounds best. After choosing it, click Stop.
  10. Click on OK.
  11. After the processing has occurred, go File > Save in Sound Forge. This saves the audio as a new take in Vegas.
  12. Close Sound Forge.
  13. Now check out the project in Vegas Pro software; the audio and video should sync together perfectly. To compare the sound quality to the original take, right-click on the audio track and choose the desired take. Of course, the original one won't be in sync with the video.

That's all there is to it!

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