It’s useful if you want to fade the level down a bit, then back up again (or vice verse). I would expect this to be a fairly common use of a “partial” fade.
When fading to or from silence it makes little difference. If we eventually have an improved “Text Envelope” then that will largely make up for this effect not being so “reversible”.
The important aspect that needs to be clear in the documentation about the “Mid-fade” setting is that increasing the value tries to “flex” the fade shape upward, but never higher than the higher end of the fade.
Similarly reducing it tries to flex the fade shape in the opposite direction but never lower than the lower end of the fade:
The further away from zero, the more “curved” the fade becomes (in one direction or the other), but is constrained such that a fade-down always decreases in amplitude and a fade-up always increases in amplitude.
Before I go into a lot of technical detail, it is my opinion that for the majority of users the technical detail does not matter. If they want to boost the mid point so as to avoid a dip during a crossfade, all they need to know is that they can do so by increasing the mid-fade amount. The mathematics behind it are largely irrelevant as long as they are able to use the plug-in effectively.
Now onto some technical details:
There are several reasons for why this behaviour is important, not least of which is to avoid clipping with positive values (as you pointed out), and to avoid phase reversal (waveform inversion) with negative values. This is also the way that it needs to be for cross-fading so that we can compensate for phase correlation.
This behaviour can also be seen in “logarithmic” curves (like the envelope tool) in which a small change in level appears to be almost linear, but when the start and end of the fade have a greater difference in amplitude, the curve is much more apparent.
Unlike the Initial Gain and Final Gain, the mid-fade setting is not calibrated in dB. Just as the amount of curvature of a log fade changes depending on the difference between start and end gains, so the curvature of this fade effect depends on the difference between initial and final gain. If the initial and final gain are close together then even at maximum or minimum settings there will be relatively little “curve”.
Re. the odd scale length:
When you click to the side of a slider (in a Nyquist plug-in), or use Ctrl+Left or Ctrl+Right, the slider moves in steps of 1/10th of the scale length.
The slider range is set to provide useful curves at the end positions and a useful range of curve shapes, in particular there is a nice “log curve” type shape when the slider is set to minimum and the Fade Taper is set to “Simple”.
With this scale there are two important curve shapes, “Equal Power” and the “legacy Cross Fade”, that occur at a setting of +0.5 (that’s just how the maths works out).
Unfortunately if the scale is set to a range of -1 to +1 (or +/- 100) then the steps go:
-1, -0.8, -0.6, -0.4, -0.2, 0.0, 0.2, 0.4, 0.6, 0.8, 1.0
which means that two of the most useful settings are quite fiddly to set.
If the slider range is -1.25 to +1.25 then the steps are:
-1.25, -1.0, -0.75, -0.5, -0.25, 0.0, 0.25, 0.5, 0.75, 1.0, 1.25
which makes it a lot easier to set the slider to +0.5
My understanding of the word “taper” is:
A thin candle (obviously not relevant in this context)
To become gradually narrower or thinner toward one end.
There is also a relevant technical use for the word, which is to describe the rate of change of resistance of a potentiometer (such as a “fader”). Most commonly these are linear taper or “logarithmic” taper. “Logarithmic taper” is sometimes referred to a “audio taper” because it is commonly used for volume controls and similar devices.
I think the word “taper” is better than “curve” because a “linear taper” is not “curved”. Not only is it the correct technical term, I think that the common usage of the word “taper” conveys the idea of a fade that is getting gradually bigger (a fade in) or smaller (a fade out).
Is there a term that you prefer? Do we go back to “Fade Shape”?
As with previous versions the “Sine” taper is a raised sine/cosine curve when the mid-fade level is set at zero. As the amount of “curvature” is increased (increasing the mid-fade), the shape becomes less “S” shaped and more “C” shaped. At a setting of +0.5 it becomes a 1/4 cycle sine curve (previously described as the “Equal Power” curve. It is still a “sine” curve, but it is no longer “S” shaped. The term “S shaped” is OK as a preset, but it is a misnomer if the curvature can be altered.
In response to your previous criticism I was trying to make it crystal clear that when “Fade In” or “Fade Out” are selected, the Initial and Final gain sliders don’t do anything.
I presume that you mean for the name of the control to be “Ignore Level Controls:”
“Ignore” will look odd when “Use Controls” is selected, more so than “Override” I think, or do you have suggestions for rewording the choices?
One major problems with including more presets is that we would need to name them.
In my opinion the presets offered in Goldwave “Fade in” are inadequate. For example there are no presets for a fade out that starts gradually and then becomes steeper (commonly required for good crossfades).
Unlike the Goldwave “Volume Shaper” we do not have visual feedback in the form of a graph (I presume that the graph changes according to the selected preset). Without seeing it on a graph, what on earth does “Attack and Fade” mean? How many of those preset names describe clearly what will happen (unless you can see the graph)?
In version 23 we have two adjustable “shapes” (tapers). The first (default) is a simple “line” that flexes from one direction, through linear to the other direction. The second is a more advanced option that allows “double curves” (“S” shaped) to be produced and “bullet” shaped curves. For novice users the “Simple” curve is likely to be adequate most of the time. The “advanced” option provides useful curves for a variety of “advanced” tasks such as crossfading songs/music.
Did we decide which way up a “log” curve goes?
To create a log type curve (similar to the envelope tool), use the “Simple” taper and set the “Mid-fade” to minimum.
The slightly odd scale on the Mid-fade slider has been carefully designed so that useful curves (candidates for presets) are those that can be set easily. So yes we could have a preset for “mid-fade = +0.5” but what are we going to call it, and do we need it as a preset if we can easily set Mid-fade to +0.5? The major advantage of having adjustable shapes rather than a lot of presets is that if you apply a fade and on listening to it you decide that it needs a bit more (or less) boost in the middle, you can Undo and make an adjustment rather than trying to work out which of long list of cryptic descriptions will give you what you want.
Exactly.
Which would be what?
“Mid-Fade Cut/Boost” will not work with “Log” or with “Equal Power”.
Yes I’d like to revamp the Text Envelope. An option for dB or % is not problematic in a “Text Envelope” type effect because a text box can accept any value you like.
