[ This article was first published in the April, 2010, issue of
Larry’s Monthly Final Cut Studio Newsletter. Click here to subscribe. ]
William Granzier asks:
Please correct me if I am wrong, but when recording an interview with a shotgun microphone on a DV camera set to AUTO level contro (ALC)l, the recorded audio can sound distorted, even though the record level shows that its not peaking in red. This is due to the camera compressing the audio when it gets to loud. Is that a correct statement.
I have always maintained that using ALC on a digital device is bad news as loud audio can sound distorted when it hits 0 dB. This is due to the sensitive nature of digital audio. My golden rule was rather drop the audio level and then use FCP Gain filter to lift it a bit if needed than have audio that sounds distorted.
Secondly an audio signal played into FCP through a deck is a direct representation of the way the sound was recorded and the audio levels cannot be adjusted upon import, only once imported can one the audio control in the timeline to adjust the level.
Larry replies: Hmmm… theoretically, ALC should not cause distorted audio, however, all things are possible; especially on lower-end gear.
I agree with you that, if possible, recording at a SLIGHTLY lower level without using ALC is preferable. However, recording levels below -18 are so low as to cause more problems with excessive background noise than they solve. I generally try to aim for recording around -6 to -12.
I also agree that when working with digital source, you are simply copying files from video tape to computer and no level adjustment is possible. Analog audio DOES allow adjustment during capture.
Also, something I just learned from conversations with Aphex, is that MP3 compression is optimized for maximum audio levels around -6 dB. AAC (MPEG-4) audio is designed to handle levels as high as 0 dB.
In ALL cases, never let audio levels go above 0 dB.