Re: [linux-audio-dev] extending LADSPA

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Subject: Re: [linux-audio-dev] extending LADSPA
From: Tom Pincince (stillone_AT_snowcrest.net)
Date: Tue Oct 24 2000 - 22:52:20 EEST


This thread seems to go against everything I thought I knew about
daw's. My guess is that individuals working on individual components
are now looking to integrate with the works of others, but are still
looking from the perspective of their individual apps instead of from
the perspective of the integrating app, the host. My experience tells
me that the host is primarily a sequencer, and I have never seen a post
to lad that addresses this. I have also never seen a post to lad that
addresses the integration of audio and MIDI. Coincidence? I think not.

Sequencers started as devices that output timed control data for
synthesizers. Since MIDI is a format for transmitting control data, it
is easy to see why the first popular computer apps for music took the
form of MIDI sequencers. A MIDI track is a *list* of control data with
each entry on this list referenced to a clock value representing the
time the host is to transmit this control data. An audio app that uses
edl's works the same way. An edl track is a *list* of pointers to the
beginning and end points of regions of soundfiles referenced to a clock
value representing the time the host is to begin and end playback of
these regions. This comparison is meant to show that, if you can see a
MIDI recorder as a sequencer then you can see an edl based audio
recorder as a sequencer. This offers solutions regarding the control of
plugins without requiring that the plugin knows anything about time.
That is *the* job of a sequencer.

>i've been playing around with ladspa, and it looks great! but i tried
to
>implement a simple fadein/out plugin, and quickly realized that i don't

>know how to get the _total_ number of samples that will be processed
>(i.e. the total user selection). i'm passed the number of samples to
>process for each block, but for something like a fade or envelope, i
>need to know the total number of sample in all blocks. where do i get
>this info? sorry if it's in the docs, but i can't find it anywhere.

The first thing to notice is the P in LADSPA. Plugins must plug into
something. A host. Your example comes from the perspective of the
soundfile, not the host that the plugin is plugged into. The short
sighted view is that these plugins are plugged into a mixer. If they
are plugged into a sequencer, then the region to be faded is defined by
an edl entry and the sequencer sends control data to an amplifier
plugin. Not only do you have fades, you have complete mixer automation,
since all functions of a mixer can be accomplished with plugins. So
Richard and Conrad's point of view make the most sense to me.

I will comment on the batch stuff soon but I am out of time right now.

Tom


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