Integrating Technology in the Foreign Language Classroom
Jean LeLoup & Bob Ponterio
SUNY Cortland
© 2008 |
Digital Sound Capture and Editing
In this lesson we will go through some basic sound editing steps using Audacity or Adobe Audition (formerly Cool Edit) for
typical applications for class projects.
1. Capture sound [File/New]
Audacity opens ready to begin recording, but you should first choose some settings to be sure that you are recording in the format that will be best for your project. Selecting the preferecnes for your sound format is done in the Edit/Preferences menu.
You can select your sound devices for input & output and also set stereo or mono recording.
You can set quality for your sample rate (44100 Hz or 22050 Hz) and your sample format (16-bit or 32-bit).
And you can choose the file format quality for export settings, for instance, mp3.
| Within Audacity, the VU meter for checking levels is always visible, but you can Satrt Monitoring or turn it on to test levels using themicrophone drop-down menu (see below). The louder the sound, the farther to the right the meter will go.
The line remains for a time to indicate the highest recent
peak.
If clipping occurs, the clip indicator at the right of the meter will
become
red.
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 You can also use the Windows Volume Control window (Options / Properties / Recording) to monitor sound
recording levels. For best results the level should be high but should never enter the
red
clipping zone. Adjust the volume accordingly.
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However, you can set volume and monitor levels directly within Audacity.
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- Avoid background noise.
- Use a good microphone. Talk across your mic, don't blow air into the mic.
- Use 16-bit samples (32-bit yields better quality for editing your working copy, though you can reduce the final copy to 16).
- Select sample rate (22050 is ok for voice depending on
desired quality;
44100
yields CD quality for music).
- Higher sample rate creates larger file size and slower downloads but better quality.
- Adjust volume to maximize the sound but avoid clipping
(if a wave is too loud, the top of the
wave is clipped off).
- Leave at least a second of silence in the recording to aid in
future
noise
reduction.
If you have trouble getting your own sound file for the following
steps, you may download a sample sound and practice editing that : soundsample.mp3. All of the manipulations of digital sound are really mathematical transformations, remember graphing functions in algebra class?
2. Center Wave (aka DC bias adjust, DC offset) [Transform/Amplitude/Amplify]
- VERY imporant step after many recordings! Your sound might not be centered for amplitude (see below for a wave that is not centered).
Centering should be done first. In Audacity, DC Bias can be found under the Normalize effect. If you have additional effects to apply, you might prefer to center the wave first and Normalize last.
- Make sure that the wave is centered before applying any other
transformation.
3. Noise reduction (FFT 8192, precision 7) [Transform/Noise Reduction] But only do this if you think it needs it.
 |
In Audacity, the noise removal effect is simpler.
- Select a few seconds of noise, then get the noise profile.
- Next, go back to your sound, and select the whole thing. You can preview before actually removing the noise. If you don't like the result, you can try removing more or less of the noise until you are satisfied.
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4. Trim [Edit/Trim]
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Audacity
When trimming, use the Zoom tool to find the precise segments that you wish to select. Listen to your selection to be sure it is what you want.
Select area of the sound you want to keep then select Edit / Trim. |
5. Listen carefully and clean up anything you don't like. To avoid
breaking the rhythm of your sound sample, reduce the volume (Effect / Amplify) of problem
noise instead of cutting it out. Using a negative dB reduces the volume.
6. Normalize [Transform/Amplitude/Normalize]
Cool Edit / Audition
- Use to ensure that all of your sound files are at the same level.
- Set to 95% then calculate. Cool Edit will select the proper
adjustment.
- Click OK to make the change.
- Whereas Noise Reduction, Noise Gating, and Compression may not be
needed,
Normalization is generally required to make your project sound good. You can do the DC Bias Adjust (Center Wave) in the Normalization window to save a step.
Audacity
 |
In Audacity, Normalize and DC Offset (aka: Bias, center wave) are found in the same Effect. Normalization is set to -3 dB or about 75% of full volume for the highest peak of your sound. All sounds in a project should be set to the same level, but you might prefer a higher volume than 75%. |
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It is possible to use the Amplify Effect in Audacity to Normalize by setting the same Peak Amplitude for each sound file in a project. -0.0dB sets the highest sound peak at the maximum sound level. Some people prefer to avoid using the maximum sound level in order to be sure to prevent clipping, so you might use -0.1dB or -1.0dB. As long as you use the same setting for all sounds. |
10. Save backup copy
- Keep a backup at the best sampling rate possible for future use.
11. Change sampling rate if necessary, but only if you are sure
- For use on the Web, it can be necessary to reduce sample rate for
faster
file transfer.
- Software such as RealAudio may require a particular sample rate.
- In general, just leave this alone.
12. For use on the Web most files should be saved as .mp3. or Real
Audio. It usually
is not useful to use stereo for most FL applications. Cool Edit 2000
does
a good job of preparing final compressed versions of your sounds.
The most important steps in sound editing are : Capture, Center Wave, Trim, Normalize.
In Audacity, the View / History feature is very nice and will allow you to undo any of the edits that you have made to a sound.
Cool Edit used to be purchased from Syntrillium Software http://www.syntrillium.com/cooledit/
But they were bought by Adobe. The program is now called Adobe
Audition. Ask about academic pricing
/ educational discounts for
teachers. It remains quite expensive. Other high quality, and expensive, tools are Pro Tools, Sound Forge, and Wavelab.
For this course, we are using a free program called Audacity. It works quite well and can do everything you will need: http://audacity.sourceforge.net/ (This requires an additional Lame plug-in to export mp3.)
A very inexpensive solution that also seems to do a good job with
sound is either MIXCRAFT Recording
Studio, about $40, from Acoustica http://www.acoustica.com/
AVS Audio Tools has an unlimited evaluation period, but also very inexpensive, about $30.
Goldwave is great in it's price range, about $45.
For more information:
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