Re: [linux-audio-dev] gain curves, interpolation, etc.

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Subject: Re: [linux-audio-dev] gain curves, interpolation, etc.
From: Paul Barton-Davis (pbd_AT_Op.Net)
Date: Wed Nov 29 2000 - 18:43:32 EET


>This sounds a bit fiddly, and you really don't want to be exposing
>exponential curves to the user, it wants to look linear, but infact the
>gain would be exponential. When I'm fading I think of the action I make
>with a slider, which is more or less linear, but the gain curve is
>exponential (or something like that).

well, there are two things here: first, most existing DAW's *do*
expose the user to exponential curves. a typical approach is to offer
a palette of possible xfade "shapes":

    out = linear, in = linear
    out = exponential, in = linear
    out = linear, in = exponential

etc.

second, as far as gain curves in general, keep in mind that as david
bartold was so kind to point out to me, macromedia owns a patent on
the use of a visible control curve to manage waveform volume. the
patent very viable to me. so its unlikely that any open source project
will work that way. i haven't figured out the generic alternative yet.

however, for edit-point xfades i am thinking more along the lines of
combining the "palette" approach with the way snd does things with a
more immediate method of specifying xfade length:

     * you get a palette of xfades, which you can add to if you really
         want to
     * the initial width of an xfade is an app-wide default
     * if you click near the xfade (possibly having selected the mouse
         cursor to function in a specific way), the duration of the xfade
         is highlighted, and you can shorten or lengthen it at either
         end, or at both ends simultaneously.

snd has the interesting approach that when you edit an "envelope", it
is shown with an x-axis from 0 to 1. then, when you apply the envelope
to a particular region of a waveform, 0 is mapped to the start of the
region, and 1 to the end. it has some real benefits, and some real
drawbacks.
         
>Often you just want a short crossfade. Select a point in two tracks, hit
>crossfade and it fades around it. If it sounds nasty you make the fade
>a bit longer. Isn't this the stuff that ProTools makes really easy?

well, i haven't checked protools in a while (BTW - did anybody
download the free version ? i think the idea of printing out the
manual is an excellent one, but haven't gotten to it yet). but i have
never thought of xfades as existing from track-to-track. they exist at
the points where you insert material from some place into a track.

ardour already does (static, though configurable) xfades for
punch-in/punch-out, but its the wrong mechanim and its not relevant to
the editing case (and thus needs to be fixed).

in case its not obvious, despite the fact that i don't plan to add a
mixer component to ardour-as-DAW any time soon, managing xfades at
edit points is most sensibly done (i think) by adding complete support
for gain curves, hence this thread.

--p


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