Using Nudge Commands

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Using Nudge Commands

Nudge commands are used to "bump" or push audio regions around the timeline by preset amounts. This is handy for fine-tuning audio placement to video by nudging regions frame by frame until they line up with the correct video frame in a QuickTime movie. When set to very small amounts such as one millisecond, nudging can finesse audio editing for more subtle effects. At the sample level, nudging can be used to offset tracks and compensate for very small TDM mixer delays induced by plug-in processing. This complex topic will be covered in Chapter 8, "Mixing to Picture in Pro Tools."

Nudging is done by selecting one or more regions in the Edit window and using the plus and minus keys (+, -) on the keypad to move the region(s) forwards (+, to the right, later in time) or backwards (-, to the left, earlier in time). When you nudge a region, the QuickTime movie will update its location to reflect the new start position of the earliest region boundary in the selection. This happens very quickly so that you can repeatedly hit the plus or minus key to move through several nudge amounts and see exactly where you currently are in the movie. Pressing and holding the plus or minus key will activate key repeat, and the region will nudge rapidly through each value along with the QuickTime movie.

NOTE

NUDGING IS RELATIVE

Nudging an audio region does not align that region's boundary with the nearest grid value. It merely adds (+) or subtracts (-) the nudge value to the start time of that region. Nudging functions like the new Relative Grid mode in version 6. The normal Grid mode will snap regions to the nearest grid value, whereas Relative Grid mode will move regions relative to grid values. If you want your audio file to start exactly at a certain video frame, you must use Grid mode to snap the region to an absolute frame point on the timeline.

Setting Nudge Values

Nudge values are set in much the same way as grid values, as shown in Figure 6.43. They can follow the Main counter's format if that option has been checked. All the preset values are the same as the grid values for each time format.

Figure 6.43. Nudge values can be selected from the Nudge pull-down menu.

You may manually enter your own custom nudge value by clicking in the nudge value number itself, as shown in Figure 6.44.

Figure 6.44. You can manually enter nudge values by clicking on the number itself.

Aligning Regions to Video Frames

A common value to use when working with video is 1 frame. This increment matches the smallest increment by which the visual image can be adjusted. Using the 1-frame nudge value makes it easy to nudge through each and every frame of a short sequence to find the key frame to which the current sound you are editing applies. When a baseball bat is swung and hits the ball, there might be 15 frames in the last part of the swing leading up to the hit. If you are placing the "crack" sound of the bat hitting the ball, you must find the exact frame at which the bat connects with the ball.

A common practice is to place your sound effect somewhere close to where you think it should be. Then using the nudge keys (+, -), nudge the sound by one frame until you see the precise frame where the effect should begin. I'll break it down.

1. Enter Grid mode with a value of 1 frame.

2. From the Audio Regions list, drag the sound effect into the timeline to a place that is close to where you think it should be. The important thing to remember is not to take too much time when initially dragging the sound effect into the timeline. Nudging the region later will provide more accuracy. Just get it close. (See Figure 6.45.)

   Figure 6.45. The "crack" sound is placed near to the frame in which the bat actually touches the ball. Notice that the ball is not touching the bat yet.

   

   
   

3. Make sure your nudge value is set to 1 frame.

4. While watching the QuickTime window, nudge the sound back (-) or forward (+) until you see the frame where the sound should start. (See Figure 6.46.)

   Figure 6.46. Notice that the QuickTime window shows the ball actually touching the bat. After being nudged, the "crack" sound now starts on this exact frame.

   

   
   

5. Play the result to see how it syncs up. It should be quite close. Even though the waveform is visually lined up exactly with the frame that shows the ball touching the bat, it might not be in the exact position yet. I'll explain what I mean in more detail in the next section.

Sub-Frame Nudging

Two factors must be taken into consideration when nudging audio regions by one frame. Just because one particular frame of film happens to have the ball in contact with the bat does not mean that the bat first connected with the ball exactly when that film frame was exposed. The ball could have contacted just prior to the opening of the shutter within the film camera. That frame caught the ball still touching the bat, but some small amount of time after they actually hit. Granted, this is a very small amount of time, but human hearing is far more sensitive to timing cues than eyesight, and so the difference in timing is perceptible. Secondly, just because an audio region begins at its left boundary does not mean that the valid audio event occurs right at the start of the region itself. Often there is a small amount of silence before audible sound begins, or the sound is structured so that the critical timing portion occurs later in the region.

Human eyesight has time accuracy down to about one-thirtieth of a second or so. That's about 33 milliseconds. At this speed, the brain is not making clear distinctions between successive images in the video. The brain is capable of constructing motion out of repeating images up to 130 milliseconds apart. This is the basic principle upon which filmmaking has been developed.

To the ear, 130 milliseconds is slap-back echo. The human ear is capable of discerning much smaller time incrementsdown to about 10 milliseconds (much smaller for audio professionals with trained hearing). If you take into account stereo-imaging delays, the factor decreases to below sub-millisecond values. For our purposes, the 10-millisecond threshold is the most relevant.

While the eye is constructing smooth motion and continuity out of still images passing by every thirtieth of a second, the ear is busy correlating sounds relating to those images. However, the ear is using much smaller increments in creating a smooth perception of time than the eye. The bottom line is that one-frame accuracy in editing for picture is just not good enough in many instances, especially in action scenes.

Using sub-frames, milliseconds, or samples will allow subtler placement of sounds. Click on the nudge value itself and manually enter a small number, such as five milliseconds, to fine-tune a region's placement once you have found the correct frame. You will be surprised how much difference a few milliseconds can make.

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