[Linuxsampler-devel] Re: resampling benchmarks, sampler module, effect sends

[Benno S. <be...@ga...>]

Paul Kellet wrote:
> Mono FX sends / stereo FX returns is the most common configuration - 
> on hardware samplers and synths, and on all but the biggest analogue 
> mixers.
Ok, but what does this mean for the the audible result of a panned mono
signal processed by a FX with mono sends ?
Eg only the try part gets panned while the wet part is still centered in
them middle ? Is this the audible result ok or does it sound bad in
extreme panning positions ? 
I'd prefer to use mono sends (as default, stereo will be possible too)
if that is the standard since it will save us some CPU cycles which
helps to increase polyphony.
 
> But hardware synths and samplers will usually have less FX sends than
> they have FX busses, so you set the send level and destination for 
> each source.
Yes of course. Since we use the recompiler we can create as many FX
sends per voice as we wish. I AFAIK the usual GM MIDI standard has two
sends for each MIDI channel.(reverb and chorus).
The flexible nature of linuxsampler will allow arbitrary per-voice
dynamically routable FX sends but in most cases this will not be needed
since when implementing a MIDI sampler we can simply mix all voices on
the same channel and then send the result to the FX since all voices
belonging to the same channel share the same FX send level.
This saves a lot of CPU.
This means the benchmarks I posted in my previous mail 
(284 voices on P4 1.8GHz , 331 voices on Athlon 1.4GHz) are meant with 2
different FX sends on a per-voice basis. With per-MIDI-channel the
performance is probably around 500-600 voices on the same boxes. This
means that there will be plenty room for running the actual FXes and
providing additional insert FXes like LP filters etc.

 
> If each effect can be chained into the input of the next effect, one 
> routable FX send may be enough.

Sorry I am no expert here, but taking the usual reverb, chorus case I
don't think they can be chained , can they ?

 
> But if you want to support "insert" effects like compression, these 
> should be on stereo busses.  So the question turns into: do we have 
> one sort of effect and use stereo FX busses, or do we have separate 
> send and insert FX (or just have FX sends, and insert effects can be 
> applied to outputs).

I think separate send and insert FXes should be supported.
They can be either stereo or mono (probably for insert FXes it makes
sense to keep them mono in the cases the sample sources are mono).

Can the concept of per channel FXes the case of MIDI devices be applied
to inserts too ? I guess yes. (eg let's say on midi chan 1 we have a
polyphonic synth sound and we want to use an insert FX (a lowpass) to
process the sound. In that case we can simply apply the FX to the
channel mix buffer, right ?

Benno

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