|Jean LeLoup & Bob Ponterio
In this lesson we will go through some basic sound editing steps using Audacity for typical applications for class projects (recording and basic editing). You can download Audacity for Mac or PC for free.
Be sure to also follow the directions in the FAQ to download & install the Lame encoder that lets you export your sound in mp3 format (mp3 is a common format that compresses sound).
In order to import and export additional sound formats that your iPod, telephone, or digital voice recorder might use (such as WMA, M4A, or FLAC), download and install the free FFmpeg library.
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 preferences for your sound format is done in the Edit/Preferences menu.
You can select your sound devices for playback & recording (which microphone do you want to use?) and also set stereo or mono recording. Mono is fine for most language class projects.
You can set quality for your sample rate (44100 Hz or 22050 Hz - how many sound samples per second?) and your sample format (16-bit or 32-bit - how precise is each sample?). 16 bit is fine for most language class projects.
|Within Audacity, the VU meter for checking sound levels (loudness) is always visible, but you can Start Monitoring or turn it on to test levels using the microphone 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 help show the highest recent
If clipping occurs (sound too loud for the equipment), the clip indicator at the right of the meter will
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.
However, you can also set volume and monitor levels directly within Audacity.
|too loud||too soft||just right|
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?), just as pretty much everything else in a computer boils down to math & logic.
2. Center Wave (aka DC bias adjust, DC offset remover) [Transform/Amplitude/Amplify]
VERY important step after many recordings! Your sound might not be centered for amplitude (see below for a wave that is not centered).
Centering should always be done FIRST. In Audacity, DC Bias can be found under the Normalize effect. You can also find the DC Offset Remover effect that centers the wave without normalizing. 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. (I know I am repeating, but this is important.)
3. Noise reduction (FFT 8192, precision 7) [Transform/Noise Reduction] But only do this if you think the sound really needs it.
In Audacity, the noise removal effect is fairly straightforward.
Without going into the details, noise reduction transforms the part of the sound that it considers "noise" into something softer. Too much noise reduction creates unwanted distortion, so it is not a magic bullet. It is better to record clean audio in the in the first place than to try to fix it later.
4. Trim [Edit/Trim]
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.
You can also select a part of the sound and simply delete it to remove or cut something.
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
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%.
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
12. For use on the Web most sound files should be exported as .mp3. It usually is not useful to use stereo for most voice-only applications. Stereo takes up twice as much room. You can choose the file format quality for mp3 export settings, for instance, mp3 lets you determine how much to compress your sound. As with images, more compression means smaller file size but poorer quality.
The most important and most common steps in sound editing are : 1. Capture, 2. Center Wave, 3. Trim, 4. Normalize, 5. Save/Export to the final version.
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.
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/ (The current version is 2.0.4, and 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 $75, from Acoustica http://www.acoustica.com/
AVS Audio Tools has an unlimited evaluation period, but also very inexpensive.
Goldwave is great in it's price range, about $59.
Free Audio Editor is another freebe for Windows.