Since the beginnings of movie-making, a clack board has been used to make a sharp noise with an accompanying visual. This is so the dialog of the actors (recorded with a sound recorder) can be synced to the motion picture later in a “dubbing” stage. If the clack board snaps shut but the sound takes place earlier or later, the sound and picture are not in sync. 

For sound engineering there is no visual only sound.

As described in my first book, Practical Techniques For The Recording Engineer, a well made recording consists of

• 1. A piano note in the key of the song
• 2. After the tuning note plays, a sharp noise (like a hand clap) to start a count-off “One”
• 3. The remainder of the count-off “two, three four, one, two three”
• 4. The song begins

The tuning note does two jobs. 

• 1. It provides an imaginary keyboard player to play a note in the key of the song.
• 2. It provides a solid note to tune instruments to should the “speed” (pitch) of the recording be changed.

Here is an example.

To make an overdub recording from anywhere in the world, here are the steps.

• 1. Record a track using the tuning note and clack/count-off as described above
• 2. Send a high-quality mp3 of this recording to the other artist who performs these steps
• 3. Open the mp3 in the free app Audacity
• 4. Add a track to record on
  
  
  
  
  
  
• 5. Overdub onto the new track
  
  
  
  
  
  
  
  
  
  
• 6. Save the combination of the original track with the overdub(s) to a new file name
• 7. Make a copy of the combination track
• 8. Edit the COPY by deleting everything from the original recording EXCEPT FOR the clack sound and the overdub track(s)
• 9. Send the clack (only) + overdub(s) back to the original artist
• 10. The original artist imports the audio (the clack sound plus the overdub) into his/her Digital Audio Workstation (DAW)
• 11. Drag the overdub recording up or down so that it is near the original clack sound recording
• 12. Slide the overdub recording left or right to line up the overdub clack spike with the original clack spike

DONE! The overdub is now in perfect sync.

It’s as easy as that.

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