Pro Tools Tip Audio Microsurgery by Douglas Murray In this article I will address three specific types of short fixes (which I call ‘micro-surgery’ on production sound) to remove these unwanted noises from dialogue tracks: Tiny clicks, which can be digital ‘snits’ (from clocking errors, for example), analog glitches (from cables or radio interference, e.g.) or even over-loud lip-smacks or tongue clicks. Short low frequency thumps or bumps, usually from physical microphone impacts or plosive consonants. Short glitches within critical dialogue that can’t be merely deleted and so require an alt replacement for the original damaged sound. Click Removal A click is a relatively loud, very short noise. Simply deleting a very short click without filling is often the most effective way to remove the problem, since a dropout of a few samples is not usually audible. The first thing to do is to find the offensive click. Playing through the problem area with the down arrow held down will cause the insertion point to move along with the play head. (I never turn on the preference ‘insertion point follows play head,’ since it is so easy to have Pro Tools do this selectively by holding Figure 1: Click selected and ready to play, with pre-roll and post-roll on. down the arrow key while playing.) When you hear the click, let up your finger and the blinking insertion point will be positioned right after the click. Scrubbing across the area immediately ahead of the blinking insertion point should reveal the location of the click quite precisely. When you finish scrubbing, the cursor should be blinking right on top of the click (if you have the preference ‘insertion point follows scrub’ on). Next, zoom in to a very close look at the click. The spike-like waveforms tend to be quite easy to see. Select what you believe to be the offensive few samples, hit the delete button, then press the space bar to play through the now repaired click. For this to work, pre-roll has to be on. I usually set pre- and post-roll to 1 and 30 seconds respectively; command-K turns it off and on when necessary (figure 1). If the click is just a few samples long, this simple deletion will probably do the trick. However, if the dropout is audible you will need to fill it with ‘air’ from nearby in the take. A few milliseconds of fill is usually pretty easy to find, but don’t duplicate the piece immediately before or after the glitch, since it may create an audible ‘stutter’ in the air. You can copy a bit of air to the clipboard, then select the dropout with the tab and shift-tab commands and use the Repeat Paste to Fill Selection command to fill just the dropout with the air on the clipboard. If there is an audible click from a waveform mismatch, try control/nudge, a sample at a time, to align the waveform in your patch with the waveforms on either side of the dropout. Another way to eliminate clicks is to create crossfades a few samples in duration around the patch. An alternate method of removing very short clicks (particularly useful on digital ‘snits’) involves the pencil tool. After locating the click and zooming in on it so tightly that you can clearly see the pattern of the audio cycles and the offensive spike, switch over to the pencil tool in freehand mode. Carefully and smoothly draw through the spike to repair the underlying waveform. Keep your artwork as short and similar to the surrounding waveform as possible. There is a small amount of ‘smoothing’ applied to your drawing by Pro Tools. Listen and undo if the repair didn’t work, then try again. One downside of this method is that you have now modified the sound file itself. Since you have probably backed up the sound files already, you will need to back this one up again. Also, if you have mirrored your files to another drive for stage delivery, the de-clicked file will need to be recopied or the fix will not appear on the other machines. A third method for click removal is to reduce the level of the click so that it doesn’t stand out against the surrounding sound level. You can do this by automating a level drop at the click location. Select Figure 2: A word with a major thump in the middle, about to be filtered. across the click in volume graph mode and use command-/ to write two automation nodes on the volume graph. Then pull the level down sharply with the grabber right over the click. Try various degrees of level pull and shape of dip. You can add nodes to create any shape of volume contour. This is one of the most powerful tools in the basic Pro Tools kit, so use it carefully. But remember – mixers can’t move their faders as fast or precisely as editors can move the volume graph in the edit room, so this is a valid editorial technique that doesn’t cross into the mixer’s turf. If you need to play the session on a system that doesn’t support automation playback (like the Akai DD8 or Pro Tools with automation read turned off), the level duck will be ignored. You can render the automation move to a sound file by soloing the track and bouncing it to disk, then replacing the original section by control dragging the bounced section from the region list onto the original track. Remember to delete the automation you used to create the dip, or you’ll be double dipping. Thump Reduction Low frequency thumps can be a problem when they occur during words. They tend to be too long to just edit out. If you can’t eliminate a thump using any of the above techniques, you can use EQ to Figure 3: The thump has been fixed above; the original glitch is below for reference. reduce some thumps to an acceptable level. First, select the thump plus a few frames on either side of it. Then, using an Audiosuite EQ, try to reduce the lowest frequencies with a high pass (low cut) filter or LF shelf filter set to cut everything below about 200 hz (figure 2). Experiment until you find the least severe setting that removes as much of the thump as possible without destroying the rest of the signal. Now make a crossfade of a few frames into and out of each end of the resulting EQed clip (figure 3). It will sound like you smoothly and precisely popped a filter onto the problem bump. You should let the re-recording mixer judge the results of a fix like this against the original un-fixed clip. So, prepare the same clip twice by duplicating it onto an alt track before doing the EQ fix to the alt version. Trial and error will help you find the best EQ setting and crossfade duration for each different bump. Alt Syllable Replacement If the glitch occurs during a word, you won’t be able to just delete the problem unless it’s very short. If the click is too long or if the bump is too broadband to remove without hurting the dialogue, you will have to replace the damaged sound with a short alternate section from another take. Figure 4: Thump selected above, alternate take synced up below. Figure 5: Alternate word smoothly replaces original with glitch. The best way to do this is to choose a section of the alt that is the same length as the glitch – in other words, very short indeed. For example, if there is a ‘pop’ on a plosive consonant in the middle of a word, find an alt version of the consonant that is clean. Line it up with the problem version on a work track and trim the fix to the shortest region that will cover the problem (figure 4). Finally, slip it across to cover the glitch. You may have to create crossfades of a few samples in duration around the alt to eliminate clicks or bumps (figure 5). The key is to find a suitable alt. The powerful technique of using the shortest patch possible to cover the problem helps to preserve the integrity of the original performance as much as possible. If the patch is a syllable or shorter, the original performance is preserved and you eliminate the need for a separately presented alt track.   Douglas Murray, a sound editor and mixer, has been using Pro Tools since version 1. He can be reached via email   Reprinted from The Motion Picture Editors Guild Magazine Vol. 22, No. 2 - May/June 2001   Guild Home | Magazine Home | Top of Page   Copyright © 2001, All Rights Reserved by The Motion Picture Editors Guild, IATSE Local 700