Part 1 described how to collect sounds, organize your files, and listen to your soundfiles for smaller your gestures. This part will outline some initial processes you can apply to your soundfiles to get interesting results. For now we will stick to Audition and Audacity for processing.
Audition uses an integrated window that contains a listing of open files, a level meter, and an editing space, among other functions. You can drag an audio file into the file list or editing space to open it in Audition. The editing space has two parts: on the top is an overview of the entire file, and the larger space contains whatever amount of the file you are viewing. You can use the top pane to zoom in on parts of the file.
As with any graphic editor, you can position the playback cursor (or playback head, if you prefer) and hit the space bar to start playing, or you can select a portion of the audio and hit space to just hear that portion. If you find a segment that is interesting on its own, you should copy it into a new file. You can copy, create a new file, and then past the audio into it (as with most programs). Audition also has a special “Copy to new” command that reduces the task to one command. If the new file you are creating is just a segment of original, unprocessed audio, you should save it with some unique name into your source files folder (for original audio).
With any audio segment taken from a longer file, you should check for clicks/pops at the beginning and end of the file. These clicks happen when you have a beginning or ending amplitude that is not zero, causing the speakers to rapidly move in a discontinuous way. You should listen to these and fix them before processing the file further. Audition has fade handles at beginnings and ends of files. Before you make use of them, make sure you have zoomed in enough so that you can know how long (in time) you are making the fade. Alternately, you can select a portion of the audio and choose Favorites | Fade in (or Fade out).
With any original soundfile you should remove extra silence at the beginning of the file before you begin processing it. As you stretch audio (slow it down), you will be stretching the silence as well if it is not removed.
effect editing with audition
Besides cut, copy, and paste, most of the other processing commands you will use are found in the Effects menu, organized by type of process. We’ll cover some basics. Keep in mind that effects are destructive, meaning that your file will change. You should use the Save As… command to save any processed audio into a new file. Save your processed files into your processed sounds folder.
Reversing audio is a simple, one step process. Remember to save your new audio as a new file.
Time and Pitch | Stretch and Pitch
Stretch and Pitch allows you to change the length of a file and its pitch. The two can be “locked,” which acts like changing the speed on a tape recorder. Making the duration longer results in the pitch becoming lower, and vice versa. If the two values are not locked, you can change duration independent of pitch. You can adjust by dragging percentage and pitch sliders, or you can double click on the displayed value to the right of the sliders and type in a specific number. You can also specify an exact duration.
In the dialog box you can preview a portion of the sound before applying the process by clicking on the play icon. Listen to the preview to see if you like the process.
Amplitude and Compression | Gain Envelope
Using the gain envelope you can create and drag breakpoints to create a new/different amplitude envelope for the file. Use it to apply attacks to steady audio, or other dynamic effects. As you drag breakpoints you will see the amplitude change in dB and percentage. If the percentage is 100% there is no change. Above 100% and you will be amplifying the audio, and below you will be reducing the amplitude. Be careful with values over 100%, as you can end up with amplitude values that are out of range. If the playback meters turn red, undo and try again with smaller amplitude values.
Filter and EQ
You have a number of choices to change the amplitudes of different frequency regions in a sound. The FFT filter lets you draw arbitrary function shapes. The EQ’s use sliders to apply amplitude changes to regions around the specified frequencies. The parametric EQ lets you create a function shape, but it is a combination of filters, and can be a little tricky to use at first. As the filters interact you get different shapes that you may not be expecting.
Being opensource/free software makes Audacity very popular for audio editing. It is a very good editor for most functions. Like audition you can drag audio files into the edit space. Each file creates a new track in Audacity, as Audacity is a multi-track editor. Since we will use a Digital Audio Workstation for multi-track editing, let’s confine ourselves to the stereo/mono editing features of Audacity.
Audacity uses its own project format to save files. Anything you want to save as a separate audio file needs to be exported. I generally select the portion of the audio I want to export, and choose the Export Selection from the File menu. If you are creating audio segments from a file, you should copy them into a new track, or after the original audio in the track you’re working on. Zoom in, apply audio fades (Fade In and Fade Out from the Effects menu), select the portion, and export to an audio file.
One note about selecting stereo audio in Audacity. If you click and move in the middle of the two tracks, you actually resize the vertical size of the tracks. You want to make sure you click and drag within the left or right channel.
editing audio in audacity
Like Audition, you will find your audio processing routines in the Effects menu, except for amplitude envelopes (discussed separately).
Change Pitch, Change Speed, Change Tempo
Audacity separates these processes, which in Audition were in one command that made use of locking (or not locking) the parameters.
Change Pitch lets you specify a pitch change without changing the duration of the audio. The way Audacity thinks of percentages is not like other programs, so it can be easiest to specify a change in semitones (with fractional semitones possible).
Change Speed changes both duration and pitch, locked together. Positive percentage changes will play the file faster, and negative percentages will play the file slower. You should experiment a bit to understand how much change you will get. Note the original time of the file, choose a percentage, and the compare it to the resulting duration.
Change Tempo is like the Change Pitch command, only it changes duration without changing pitch. Beside using percentages like Change Speed, you can specify the ending duration in seconds.
All editing commands in Audacity have a Preview button, like the preview play icon in Audition.
The equalization effect in Audacity allows you to either draw curves or adjust sliders.
creating an amplitude envelope in audacity
Audacity changes amplitude over time (envelope) through the use of a tool and manipulations in the edit space. You usually begin in Audacity with the selection tool (the vertical slash, like a text insertion icon). Next to it is the envelope tool.
Note that when the envelope tool is selected there are purple lines above and below the graphic waveform display in each track. Mouse over them and your cursor becomes the envelope tool icon. Click to insert a break point. Drag break points to create envelope segments. You can hear the effects of your changes by playing the audio file.
When you like the envelope that you have created, you need to render the change. (Up until this point your editing has been non-destructive.) Choose Tracks | Mix and Render to apply the audio envelope. Save your processed audio as a new file.