3
Audio Synchronization Exercise
When editing video cutaways, it’s typically easier to edit all of the audio first, then work on video replacements. By contrast, when adding narration to a video, it’s best to edit the video first, then synchronize the audio. Since you know the precise lengths of the video clips, you can match the audio by using a combination of rehearsed narration and audio editing. The following exercise asks you to take a short video on electromagnetic fields and add a narration track.
Audio Setup
Most audio capture and editing software needs to be set up virtually ever time it is used. Always check these three major areas:
Hardware. The software must know the input and output sources for your audio. To complicate matters, if may depend upon the operating system for some or all of this hardware information. Start by checking your system control panels for sound. Make your choices from the lists of input and output devices (check connections or drivers if the device you want is not offered as a choice). Unfortunately, the names of devices in system settings don’t always correspond clearly to information on the physical devices. Audio controls such as volume and gain can typ ically be set by either a visual indicator or percentages. Initially, set volume to about 75% of the available volume range and gain to about 30% of its available range. Use a clear speaking voice to test settings. Be prepared to tweak these settings after some audio test samples. You may have to duplicate these same settings in your software.
Storage. Audio software works with both temporary and permanent storage. Look for preferences to set temporary or scratch disks, even specific folders. Default settings, like “largest volume” or “startup disk,” often cause problems. Pick a specific hard drive that has plenty of space and appropriate access privileges.
Format. Determine the audio format, codec, sampling rate, and mode (mono, stereo) that suits your current project. Set the recording settings accordingly. For PCs, the format is usually .wav; for Macs, aiff. Uncompressed audio gives you options of later compressing in various formats but consumes large amounts of storage space. Mp3 is a good general-purpose compression technique for both voice and music. Voice sampling rates can go as low as 22050 samples/sec (half CD quality). Use 16-bit and mono for web purposes. Music will require higher quality settings (sample at least at 41100).
Now you’re ready for a short test recording. Any settings problems should be immediately evident (files don’t save, size is too large, audio quality is unsatisfactory). Adjust settings till the audio is optimal.
In the magnified waveform to the right, the audio peaks in the left half are clipped (square tops and bottoms) because the sound was louder than the recording range. Those waveforms in the right half are within the desirable 80% range (pointed tops and bottoms). If sounds are clipped, lower the volume and or gain or position mouth further from microphone.
Special Resources
Files. On the PowerBooks you’ll see a 401X folder on the desktop. Inside it locate a folder entitled “Audio Sync Project,” which contains all of the resources for this exercise: a QuickTime movie (Bulb-in-Microwave.mov), a folder (Bulb-in-Microwave Storyboard) containing a basic video storyboard (Bulb-in-Microwave.fp5), a folder (Bulb-in-Microwave Scripts) with two scripts (bulbcommentary.doc with notes that can be turned into a narration for the video; bulbscript with a sample narration that could be used with the opening title clip of the video), an iMovie folder of the video, and a folder (Bulb-in-Microwave Audio) with a sample narration file for the introductory clip.
Software. Work in pairs to record some narration audio synchronized with the video of Bulb-in-Microwave.mov. Minimally, you’ll use three applications simultaneously. In Microsoft Word, you’ll have a file of notes for the narration and one displaying the final script for the clip you’re currently recording (consider it a crude teleprompter). In QuickTime Pro you’ll have the Bulb-in-Microwave.mov open so you can watch it as you record the narration and so you can locate specific clips. In Peak DV you’ll be recording your narration. If you wish, you may also open iMovie or Storyboard Pro to gather other information about the video as you compose your narration script.
Hardware. Use LabTec Verse 704 USB microphones. You probably won’t need headphones since we’ll use several different rooms to minimize background noise.
Rooms. For this exercise you may use the following Ross Hall rooms: 22, 137, 215, 401. Two or three pairs can work in 22 and 137, only one pair in 215 or 401.
Purpose
This exercise should acquaint you with basic techniques for recording and synchronizing audio with a finished video:
· rehearsing a narrative script to achieve a close-to-sync audio recording that will minimize later editing
· setting up a typical audio editing program for recording
· coordinating three or more software programs simultaneously during audio recording
· basic time-based editing of audio files
· merging audio and video tracks
Task
Get a feel for the exercise by watching the Bulb-in-Microwave.mov video. It demonstrates a simple experiment using a microwave oven to create glow in a standard light bulb. The narration that you will add will explain a little of the electromagnetic physics that explains why the bulb glows. Next look at the storyboard for the video and at the bulbcommentary.doc file that contains notes you can use to create a narration script for the video. You’ll be working on this exercise today and next Tuesday. You may not be able to complete the narration for the whole script; just do what you can during these two classes. Although you’ll be working in pairs, you should create two separate final videos. You may use the same script if you wish, but record your voices separately. Here’s the basic procedure.
Audio Setup. Plug in your Labtec microphone and press the green button to turn it on. Set the preferences indicated in the Audio Setup section. Start by selecting System Preferences in the Apple Menu and then select sound. Under the input tab, select AK5370 (believe it or not, that’s the Labtec microphone). Use your voice to test the input volume, adjusting so that your loudest sounds don’t exceed 80% on the input level indicator. If the indicator lights up with no one speaking, you’re picking up ambient noise; lower the input volume a bit till the level light disappears or nearly so. Set the output volume to maximum. You may have to tweak these settings later once you record some sample audio. Locate Peak DV in the dock and open it. Under its Preference Menu set the Scratch Disks to a specific folder called Peak Workspace inside the 410X folder. Under the Audio Menu set the Record Settings and the Hardware Settings. Use the aiff audio file format, mono, 16-bit, an Auto sampling rate (or start with 22050 and increase later if sound quality is not satisfactory). Make sure the AK5370 is selected as the input device. Increase the buffer, perhaps to 1024. Input level may or may not be adjustable (depends on the input device).
Video Setup. Open the Bulb-in-Microwave.mov in QuickTime Pro. It automatically opens a copy. Use Save As . . . to rename the copy (add your last name) and relocate it in your student folder (410X>Student Folders>). Place the QuickTime video in the upper left of the window and position playback to the start of the video.
Script Setup. Open bulbcommentary.doc and bulbscript.doc from the Bulb-in-Microwave Scripts folder. Decide on a sentence to accompany the title opening clip of the video (use the commentary notes for ideas). Replace the text in the bulbscript.doc file with your new script. This file is already sized for easy reading. Position the document window in the upper right so you can refer to it when recording.
Recording. Start recording in Peak (command-R, Record under Audio Menu, record button ). The audio meter will show sound levels.
Now move to QuickTime Pro. Position windows so that you can see both the QuickTime video and the current script. Start the QuickTime video playing. Narrate your script. Go back to Peak and stop the recording. Save the file with a meaningful name and a version number (bulbintropayneraw1.aif) into your individual folder. Test playback quality (spacebar starts and stops playback) and adjust any settings, especially volume levels or sampling rates. Continue this process. Record the same sentence several times in a row, working on improving your delivery (clarity, expressiveness) and on matching your script to the time segment of the video clip.
Audio Cuts. If you rehearse the recordings, you should have a good quality clip whose primary problem will be excessive length. Use Save As . . . to create a copy for editing (named appropriately). Select pauses and silences, reducing the clip to precise the length of the video clip. Use the zoom tool for finer deletions. Save the final versions. Repeat for each video segment. Create a new file in Peak for the final narration track. Assemble your audio by cutting pasting in sequence your individual segment audios. Check total time (55:05 for the total video). Save the file. You can, of course, assemble the final track as you go, using track merger to confirm that video and audio are properly synchronized before moving to the next clip segment.
Track Merger. Open both the original video track and your new narration audio track in QuickTime Pro. In the audio window, choose Select All (command-A) from the Edit Menu and then Copy. In the video window, choose Select All and then Add (command-V). Test your new video and save it. Link a copy to your class homepage.