Re: [ecasound] LADSPA latency ouput value

I have read the following discussion:

http://ardour.org/node/761

they says that LADSPA spec include a latency report using a output.
Ardour have a delay compensation mechanism which read latency of each
plugins.

Quoting :

Steve Harris and I came up with a kludge solution for LADSPA (an output
control port called “latency”), and a few other LADSPA developers
supported it. in VST, its a host->plugin callback called
getInitialDelay().

ecasound in verbose mode display outputs of LADSPA plugins which contain
the latency output but the value is read at initialisation time so it is
not the effective latency !

If you have the following package installed :

ladspa-sdk
swh-plugins

You can analyse the LADSPA plugin I use :

analyseplugin /usr/lib/ladspa/fast_lookahead_limiter_1913.so

Plugin Name: "Fast Lookahead limiter"
Plugin Label: "fastLookaheadLimiter"
Plugin Unique ID: 1913
Maker: "Steve Harris <steve@plugin.org.uk>"
Copyright: "GPL"
Must Run Real-Time: No
Has activate() Function: Yes
Has deativate() Function: No
Has run_adding() Function: Yes
Environment: Normal or Hard Real-Time
Ports: "Input gain (dB)" input, control, -20 to 20, default 0
        "Limit (dB)" input, control, -20 to 0, default 0
        "Release time (s)" input, control, 0,01 to 2, default 0,5075
        "Attenuation (dB)" output, control, 0 to 70
        "Input 1" input, audio
        "Input 2" input, audio
        "Output 1" output, audio
        "Output 2" output, audio
        "latency" output, control

which display the output latency !

Is there a way to display this output at the end of the mixing
processus ?

Thanks,
Julien.

Le mercredi 18 février 2009 à 02:54 -0800, Sergei Steshenko a écrit :
>
>
> --- On Wed, 2/18/09, Julien <julien@recisio.com> wrote:
>
> > From: Julien <julien@recisio.com>
> > Subject: [ecasound] LADSPA latency ouput value
> > To: ecasound-list@lists.sourceforge.net
> > Date: Wednesday, February 18, 2009, 1:48 AM
> > Hello,
> >
> > I use LADSPA plugin with ecasound (one plugins at the end
> > of the chain
> > setup) but the output latency of the plugin is not use (or
> > display) by
> > ecasound !
> >
> > Do you plan to adjust the output file according to the
> > latency output of
> > the plugin use. For example if the plug have 7ms of
> > latency, I will have
> > 7 ms of silence at the beginning of the output file even if
> > the input
> > file contain sound in the first 7 ms. The end of the file
> > is just
> > truncate : the last 7 ms of the input file is not present
> > in the output
> > file because of the latency offset.
> >
> > It would be nice if you can "offset" the output
> > file, or another way to
> > work around this issue is to just display the value return
> > by the LADSPA
> > plugin on the "latency output".
> >
> > I really need this information in order to synchronize
> > file.
> >
> > Thanks,
> > Best Regards,
> > Julien.
> >
> >
>
> Julien,
>
> off the top of my head LADSPA plugins do not report latency - AFAIR not
> part of LADSPA spec.
>
> Furthermore, FFT-based plugins may have huge latency, e.g. 1 second -
> depends on the task.
>
> In more general terms - FIR filter works with its worst/longest latency,
> while IIR filter starts producing sound more or less immediately - provided its FIR part is short :-).
>
> So, I guess, the only choice you have is to measure/calculate latency
> yourself and to adjust your setup accordingly.
>
> Regards,
> Sergei.
>
>
>

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Received on Wed Feb 18 16:15:01 2009