1 Reply Latest reply on May 8, 2010 9:45 AM by the_wine_snob

    Audio Dropout on Export & DVD/BD Burn

    the_wine_snob Level 9

      While working on an issue in the PrPro forum, it came to my attention that some cameras do not produce Audio the way that others do. This might come into play with certain users.


      The problem: Audio plays fine in PrE/PrPro, and in most players, but when the Project is Exported/Shared, certain Audio passages drop out, or become very faint. The same thing happens when one burns to a DVD/BD.


      Everything checks out fine, but there is a "phantom" attenuation of certain Tracks or certain Clips.


      The potential cause: some cameras produce a 1-channel Audio stream (Mono), but then create a 2-channel output file (Dual-Mono), similar to what the Audio Effect>Fill Left/Fill Right. However, there is one MAJOR difference - the second channel is laid down 180 degrees out of phase to create a faux Stereo! This will often not be heard in the NLE program, or even in a player. The Waveform looks fine, and utilities like G-Spot, do not really show this up, as they do not check the phase of the two streams. It is in Export, where one channel basically cancels out the other from partially to fully. Same thing happens, when one burns to a disc.


      The cure is to take the Dual-Mono material into an audio editor, like Adobe Audition, and reverse the phase of one channel's signal - do a Save (I'd make sure to use 48KHz 16-bit PCM/WAV), and replace the camera's Audio Clip(s) with this file.


      The 180 degree Out-of-Phase technique can be used, in some instances, to attenuate, or eliminate certain frequencies in an Audio file, though it takes a lot of tweaking. It is also used to create the faux Stereo, like here, but can be very, very problematic.


      If you find that upon Export, or Burn, you are suddenly loosing Audio in the camera stream/Clips, check the file carefully for the Phase of each channel.


      Hope that this helps, and I wish that I had a list of cameras, that use this technique.