[Clam-devel] does ladspa increase latency ?

[Pau Arumi]

En/na globot ha escrit:

"does ladspa increase latency"
yes. specifically when jack (or other backend) uses a buffer size <
  512.

the latency is determined by the LadspaWrapper audio in/out port
sizes, which is hardcoded to 512.
this is not only limited to ladspas, most time-domain processings
get the port size from the network wich is also hardcoded to 512.

ok, regarding latency, this is an important flaw. it is a known
flow and fortunately easy to fix as well. it's a matter of exposing
the host (or backend/network-player) buffer size to the
processings. and the sample rate as well, for the matter.

as we use to develop new features driven by necessity i think you
give us the perfect excuse here :)
i've been working on a patch this afternoon but didn't had time to
finish it (found some difficulties with JackNetworkPlayer
initialization). i'm attaching it as is now just in case anyone
wants to continue from there. i'm afraid i won't have the chance to
write code till first of september.

note that the patch is not ready. it will assert on NE loading.
parameter propagation is still not in place but all needed
interface is there.

cheers!
pau


> 
> hi,
> 
> today i was testing ladspa plugins (because there is a lot of usefull 
> things in ladspa), but i still need realtime processing, and i have 
> mesured some increase in latency when using ladspa plugin. The increase 
> is made in such a way i can't get my network running under 310 frames of 
> latency between a micro and outputs.
> 
> the network is simple: input -> gainIn -> EQ -> gainOut -> output
> all measurements are done with a sample rate of 48000Hz
> ____________________________________________________
> if EQ = FFT_fftw3 -> 3BandFilter -> IFFT_fftw3
> and gain is made with the CLAM::AudioMixer
> buffersize is set to 32
> i get around 150 frame of latency.
> _____________________________________________________
> if EQ = FFT_fftw3 -> 3BandFilter -> IFFT_fftw3
> if i remove gainIn and gainOut and connect directly
> i get aroud 118 frames of latency.
> _____________________________________________________
> if EQ = FFT_fftw3 -> 3BandFilter -> IFFT_fftw3
> if for gainIn and Out i use ladspa plugins (id 1181, simple amplifier)
> i get around 320 frames of latency
> _____________________________________________________
> if EQ =  multiBandEQ (ladspa plugin id 1197)
> and use ladspa plugins (id 1181, simple amplifier) for GainIn and Out
> with buffer size of 32
> i get around 329 frames of latency
> _____________________________________________________
> if EQ =  multiBandEQ (ladspa plugin id 1197)
> and gain is made with the CLAM::AudioMixer
> with buffer size of 32
> i get around 329 frames of latency
> _____________________________________________________
> 
> the thing that seem strange here is for the test 4 and 5, because if i 
> increase the buffersize for the ladspa Equalizer, my latency change (if 
> i set 64 for the ladspa EQ buffer size, i got around 360 frames of 
> latency) but i still got a mysterious latency that is added to the theory.
> 
> All the latency values given are approximative (maybe a few frames of 
> difference) because my eyes was tired of watching supper zoomed in 
> sounds. :)
> 
> to  get those result i take tow computer, divide the micro cable in two 
> one for PC1 input 1, one for PC2 input 2, then i take the output 1 of 
> PC1 to the input 2 of PC2.
> PC1 is for sound processing, and PC2 is for measurment
> 
> MIC --o---> (in1)PC1 (out1)
>      |                 |
>      o---> (in1)PC2    |
>            (in2)<------o
> 
> 
> PS: use fixed font with to read this message
> 
> 
> 
> 
> 
> 
> 
> 
> _______________________________________________
> Clam-devel mailing list
> Clam-devel at llistes.projectes.lafarga.org
> https://llistes.projectes.lafarga.org/cgi-bin/mailman/listinfo/clam-devel

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