Proposal Log / Linear Envelope Option

Proposal pages help us get from feature requests into actual plans. This page is a proposal to improve the Envelope Tool.

Proposal pages are used on an ongoing basis by the Audacity development team and are open to edits from visitors to the wiki. They are a good way to get community feedback on a proposal.

• Note: Proposals for Google Summer of Code projects are significantly different in structure, are submitted via Google's web app and may or may not have a corresponding proposal page.

The Problem

The current implementation of the Envelope tool using log/exponential fades is fiddly and not flexible.

• It is difficult to create a fade in with a large slope at the beginning and a low slope at the end
• Conversely it is difficult to create a fade out with a low slope at the beginning and a high slope at the end
• It is impossible to fade to/from zero
• It is possible, but very fiddly, to create an S-curve fade

Proposed Solution

Change to linear fades.

Pros and Cons

Pro

• easier to create any fade shape
• an approximation of a log/exponential fade can be easily approximated with straight lines, but the reverse is much harder

Cons

• old projects using log fades would need to be handled gracefully
  • this could be handled in at least three ways:
    • log fades are replaced by a linear approximation using 4 or so new control points
    • the user is warned, and log fades simply become linear fades
    • both the log and linear rendering code is retained, and the appropriate code is used according to the version number in the AUP file
• new projects opening in an older Audacity would render the new linear fades incorrectly

Other Changes

• alt/option-click to create a control point
• alt/option-click to delete a control point
• click to select a control point
• arrow keys can be used to move a selected control point

QA Backing

• Bill Wharrie
• Steve