Editing Using The Waveform Display

The waveform display can also serve as a user interface control. Most often the waveform display is used as an interface to define selections of audio on which to perform edits. This practice is so common that a whole group of software can be discriminated that has a waveform control as centrepiece of the user interface: the wave editor.

Basic Selection

The simplest user action is to click45 _{on the waveform. A single click will} specify a point in time within the waveform, which can be used as start point for playback, or to position a marker. Markers serve as an aid for subsequent selections, indicating points of interest. Selecting a segment of audio can be performed by clicking and then dragging over the waveform along the time axis, defining a start and end point. The selected segment can now be separately edited, without affecting the unselected audio. Audio selection will be discussed further in the following chapter, “Smart Selections”. Here, the manipulation of a selected segment will be discussed.

Axes

The waveform display represents audio as amplitudes on the vertical axis, along time on the horizontal axis. A selection on a waveform display is only a selection along the time axis. Selecting a range of amplitudes might serve useful only for processes for which a more fitting user interface already exists46_.

Basic editing actions on a segment of audio are cutting, copying and pasting. This way, audio can be moved, removed, and duplicated, just as one might do [45] In this thesis, for the examples of user input the combination of computer mouse and keyboard is used as input device, which currently is still the most predominant input method. [46] One example might be wave shaping, mapping amplitudes to different amplitude values.

with text in a text editing application. Along this resemblance, a less common procedure in audio editing is repositioning, “grabbing” a selected segment and dragging it along the time axis to the desired position.

So far, these basic editing procedures do not alter the audio within the selected segment. Considering the two axes along which our user interface actions might operate, two types of transformations can easily be applied. Stretching the selection along the time axis can equate to time-stretching the audio. This is becoming a common practice in modern music production

software such as Apple’s Logic (“Flex Time”) and Ableton Live (“Warping”), where it becomes a powerful tool when for instance synchronising a sampled piece of music to the beat of the final project.

As the selection is only a selection on the time axis, it cannot be stretched out vertically. Therefore a horizontal line inside the selected segment (either along zero amplitude or along the bottom of the display) might be used to present a value that can be shifted up or down. Shifting along the vertical axis can be associated with a gain change, as this will change the amplitude up or down (see figure 22). An example of this can be seen in Adobe Audition. A less straight- forward association may be pitch shifting, often appearing paired with time stretching and therefore a suitable candidate for the vertical axis transformation. Pitch being conceived as relatively “higher” or “lower” to another pitch is also strongly directionally associated with the vertical axis.

Modifier Keys

Time stretching and pitch shifting are but two possible processes that can be applied by manipulating the waveform display. Looping a selection by extending it along the time axis can be desirable in (combination with) music production software such as Apple’s Garage Band. Considering the loudness war (Katz 2007), dynamic compression by dragging along the vertical axis (louder, louder!) is conceivably also convenient. In any way, the employed process might be replaced through a settings menu, or alternated using so-called modifier keys. These keyboard keys, among which most common the

Figure 22. A waveform display that provides gain adjustment by dragging up or down. Other parameters can be adjusted using moderator keys (see bottom-right).

Shift, Control, Alt and Command key, modify the behaviour or action of other computer keyboard keys and mouse actions. As figure 22 illustrates, a possible implementation can have gain change as the default vertical axis process, while pressing the Apple Command key ( ⌘ ) to alternate this to pitch shifting, or pressing the Apple Option (or Alt) key ( ⌥ ) to alternate to high pass filtering. Combinations of modifier keys, such as Command + Shift, can extend the number of available processes even further47_.

Transitions

The waveform display in figure 22 also provides a basic means for parameter automation. In the illustrated example, the gain is increased for the selected audio. The unselected audio is kept unchanged, which can be regarded as having a gain change of zero. On the left side of the selection, the direct

transition from unchanged audio to the increased gain within the selection will be unpleasant audibly. On the right side of the selection, a transition area is defined by dragging a handle at the top of the display apart from the selection. Within this area a smooth transition from increased gain to zero is performed by

automating (meaning to automatically change) the gain parameter, making the

audible result more pleasant. Some audio editing software (such as Audiofile Engineering’s Wave Editor) incorporate this approach to create fades (fade in / out) at the edges of a selection, but no other effect parameters can yet be automated this way. Parameter automation will be discussed in detail in chapter 3.6, “Sonic Composition”.