The digital domain permits not merely composing with sounds, but composing the sounds themselves.
3.6.1 Parameter Automation
Parameter automation is a technique that is mainly found in multi-track audio editors and DAW’s. These kinds of software allow the user to apply [64] A mute is a device fitted to a musical instrument to alter the sound produced, by affecting the timbre, reducing the volume, or most commonly both.
[65] Trevor Wishart describes in detail the “human repertoir”, the possibilities of the human voice, in his book On Sonic Art (1996, p.263).
effects to a single track. Then, using parameter automation, the settings of these effects can be changed over time. This generally works by defining an envelope curve. This curve runs parallel to the audio waveform, giving the user a visual guide to determine where to set breakpoints in the curve. Curves for different parameters can be overlapped, making it possible to easily synchronise changes in various parameters.
In an audio editing environment which does not use the notion of tracks and track-wide effects, automating parameters is far less common. In such an environment an effect is selected, specified and then applied destructively. The dialog in which the effect settings were specified is then closed, losing any reference to the applied effect with its specific settings. Parameter automation requires a non-destructive approach (and hence a persistent reference to the effect) to allow the automation curve to be adjusted. The modular, non-destruc- tive approach to applying effects that was described earlier, provides a means to keeping reference to effects and parameter settings and can therefore provide a structure for parameter automation.
Whenever an effect is selected, it will be displayed as a module in the editing chain. Its parameters can be set to a specific value, but can also be selected for automation. A curve representing the parameter value over time is displayed below or on top of the waveform. An important point is that the waveform here displayed reflects the audio state on input of the effect. If the waveform reflects an earlier state, the timing or length of the audio might have been altered by a preceding effect.
Due to the offline nature of the modular approach, it requires all effects in the chain, or at least up to the effect the user is currently setting, to be rendered first before the parameter automation is audible. However, it also allows for parameter automation on offline effects. A simple example of what could be achieved this way is gradually increasing the playback speed66 of an audio file.
Defining a curve
An envelope curve used for parameter automation is often a segmented line defined by a number of breakpoints. By default, values between points are derived by linear interpolation. Some audio editors, such as Adobe Audition, also offer a spline curve
interpolation67 for smoother transitions along breakpoints, which also is more appealing audibly.
Defining a curve can be done more
[66] Known by an old-fashioned term, Tape Speed Variation is playing an audio file at a different rate, resulting in time-stretching and pitch-shifting.
[67] A spline curve is a curve constructed to pass smoothly through a given set of points. The values between the points are derived from this curve.
Figure 37. A head-up display for defining a parameter automation curve.
detailed when adding a non-graphical overview of the breakpoints, for
instance listed in a head-up display (or HUD68, see figure 37). Per point the exact value and time position can be inputted. By default, the parameter value will change linearly from one point to the following. Specifying an interpolation or smoothing function between a point and its preceding point will make the parameter value change smoothly.
For now this HUD will only add a level of precision in defining a parameter automation curve, but further on in this chapter the added value of the HUD will be made more clear.
Selections
When applying an effect to only a selected segment of audio, one of two approaches to parameter automation can be taken. Either the parameter value is deduced from only the selected time segment of a curve that spans the full length of the audio file (figure 38-a), or a curve is defined that will be applied relatively to the length of the selected segment (figure 38-b).
Both approaches appear to have a downside. In the first case, defining a curve of which only a part will be used seems unnecessary. The parts of the curve outside of the selection are not used, so there is no reason for them to be defined. In the second case, positioning breakpoints graphically makes less sense because the points at which breakpoints will be effective will be different when applying the curve to a different (smaller) audio segment. However, the latter case is preferred, when we look at applying curves to multiple selections.
Applying an effect to multiple selections is comparable to applying an effect to multiple files: a batch edit. A simple scenario might be to fade in at the beginning and fade out at the end. How much time is taken for the fade might be fixed, say 0.5 seconds, but it might also be relative, such as 10% of the total duration. Using the HUD one can define for each setting if its position is fixed [68] A head-up display is a transparent, commonly small display component in the graphical user interface. It can be moved around and miniaturized so that it interferes very little with the users gaze. It is used mainly for displaying additional information, but can also contain adjustable parameters.
Figure 38. a) A curve that spans the full length of the audio file. b) The same curve but applied relatively to the selected segment.
or relative. A fade out at 10% before the end effectively starts at 90% of the total duration of the selected segment. Now, to all selected segments a fade in and fade out can be applied uniformly, without having to define a curve for each segment.
Segment Tables
Having multiple segments selected, another way of automating parameters can be introduced. Where the earlier described envelope curve would define a parameter value at a specific point in time, it can also be interesting being able to define a different parameter value for each individual selected segment. Enumerating segments on one axis and parameter value on the other, a curve can be defined passing through these segments, effectively resulting in a table with parameter values per segment index. This for instance makes it possible to apply a gain of 0 to the first selected segment, gradually increasing the gain over consecutive selections until a gain of 1 is applied to the last selection (figure
39a). The curve can be set to a fixed number of selections, but a relative curve
as just described is more flexible in use, particularly when using automated selections, which can result in an unexpected amount of selections.
It becomes truly flexible when using a segment table to define an automated selection.
The table can now be used to specify an aspect of each selection that will be created, such as length or relative starting position, and for time-frequency selections the lower and upper frequencies (figure 39b).
These two uses of segment tables, for defining per-segment parameter values as well as automated varying segment selection, is particularly interesting regarding the aforementioned brassage technique (Wishart 1994a, p.60), which is based on cutting up, altering and repositioning audio segments. For example, an automated selection is made separating an audio file in a number of segments. Then – similar to increasing the playback speed gradually along the file – for each segment a different playback speed can defined, resulting in a stepped speeding up of the audio. Segment tables are also suitable for other sonic composition techniques described by Wishart (1994a, p.55), such as granular or waveset based transformation and repetition techniques. Grains are normally in the region of 10-100 milliseconds long (Roads 1996, p.168) and
Figure 39. a) A segment table to gradually increase gain over consecutive selections. b) A segment table specifying automated selection segment length.
wavesets are only the distance from a zero-crossing to a third zero-crossing (Wishart 1994a, p.17). Using an automated selection, these short segments can be selected, on which then techniques such as incremental repetition or varying pitch shifting can be applied.