tynet-lichat/shirakumo - IRC Chatlog

19:01:50 shinmera Okey, ported the compressor as well.

19:01:56 shinmera No sidechain, but that's Ok for now.

19:02:13 shinmera Only thing left in that lib I'm looking at is the reverb.

19:06:35 shinmera Wew, needs a 2MB support structure.

19:06:54 shinmera wonder if this thing is even RT-ready.

19:44:01 SAL9000 reverb effects usually introduce latency -- it's still RT-ready if each processing step (N samples in, N samples out) completes within deadline, no?

19:44:25 shinmera Well yeah

19:44:42 shinmera My worry is that, with that much auxiliary data, it won't complete within the timeslice.

19:45:04 SAL9000 How big are your timeslices?

19:45:25 shinmera depends on the latency you allow :)

19:46:02 SAL9000 well, the "pro audio" guideline is 10ms round trip

19:46:06 shinmera iirc in Kandria it's defaulted to 5ms buffers, but the actual time you have to fill the buffer in is of course much less than that since there's much other work to be done, too (decoding, mixing, playback)

19:47:01 shinmera wait, no, 0.05s buffers in Kandria, so 50ms?

19:47:03 shinmera I can't brain

19:47:24 SAL9000 0.05s is indeed 50ms

19:47:34 SAL9000 but that doesn't necessarily mean 50ms of latency

19:47:56 shinmera sure.

19:49:03 shinmera I'm also intending on adjusting the reverb parameters at runtime. Wonder if that's feasible, too.

19:49:17 SAL9000 watch out for "zipper" effects? not sure if that's the right term.

19:49:18 shinmera (I know it is in general, talking about this implementation)

19:49:26 shinmera SAL9000: I have no idea what that is

19:49:38 SAL9000 I haven't poked into this area for a while, so my memory is spotty

19:50:00 SAL9000 a trivial example: say you have a volume control (with unlimited slew rate)

19:50:10 SAL9000 your input is a sine wave, for simplicity

19:50:34 SAL9000 if you apply volume adjustments at anything other than a zero-crossing point, you risk creating an audible discontinuity if the slew rate is high enough

19:50:47 SAL9000 (yes, I've observed this in practice)

19:50:47 shinmera sure.

19:51:26 SAL9000 delaying the input adjustments is "enough" for simple stuff like gain or eq -- not sure how to "de-zipper" something like a reverb, though.

19:51:54 shinmera you smooth the parameter change itself.

19:52:03 shinmera using something like https://www.musicdsp.org/en/latest/Filters/257-1-pole-lpf-for-smooth-parameter-changes.html

19:52:19 SAL9000 I guess capping slew rate is a reasonable answer.

19:52:47 SAL9000 You can treat e.g. wet/dry mix as 2x gain and use step-at-zero-xing for those.

19:53:00 SAL9000 the more complex reverb params you'd have to smooth though.

19:53:20 shinmera https://github.com/velipso/sndfilter/blob/master/src/reverb.h#L263-L282

19:53:41 shinmera I'm quite sure this implementation is overkill and I could get away with something much simpler.

19:53:55 SAL9000 probably

19:54:05 SAL9000 I'm guessing you want "indoor/outdoor" reverb fx for kandria?

19:54:26 shinmera I want reverb that changes depending on how "tight" the environment is based on raycasts.

19:54:39 SAL9000 hmmmmm

19:54:47 shinmera As shown here https://www.youtube.com/watch?v=BrUQdd96qzk&t=1307s

19:55:06 SAL9000 I wanted to bring up IR-convolution as an option.

19:55:15 shinmera Yeah nah

19:55:28 shinmera Making /that/ smooth is even more difficult :)

19:55:51 SAL9000 It's more suitable for a small set of environments (small space, large space, outdoors), but it could work if you generate new IR's based on raycast data?

19:56:24 SAL9000 Smoothing between different IR curves could be done as a crossfade between 2 different convolving filters

19:56:26 shinmera Generating IRs is a very heavy process.

19:57:01 SAL9000 Set of pre-generated IRs + mixing of IRs and/or wet/dry mixing?

19:57:07 shinmera Listen

19:57:08 SAL9000 Just throwing things at the wall here :-)

19:57:16 shinmera I'm sure I can get something done like shown in the talk

19:57:34 shinmera The only thing i'm unsure about aside from the exact parameters is that one triangle thing in the diagram.

19:58:14 SAL9000 "Collision Rate/Material"?

19:58:31 shinmera That's illustrating how the parameters are changed

19:58:53 SAL9000 I suspect that one's a gain block.

19:59:04 SAL9000 i.e. "how much does that surface deaden sound reflections?"

19:59:31 shinmera hmm.

19:59:50 SAL9000 Delay -> Gain -> Low-Pass Filter -> All-Pass Filter

20:00:05 SAL9000 (tbh I still don't grok what all-pass means and why one wants it)

20:00:26 SAL9000 ohhhhhh.

20:00:50 SAL9000 "Collision Rate / Material"... as in, the combination of "how many rays hit this surface" and "what kind of surface is it", perhaps?

20:00:55 shinmera yes

20:01:15 SAL9000 more rays = louder, stronger deadening = quieter, thus the division

20:02:00 shinmera As for why all-pass, this article explains a bit https://www.earlevel.com/main/1997/01/19/a-bit-about-reverb/

20:03:08 selwyn back 2 the 90s

20:03:09 shinmera Anyway, I /am/ going to port that crazy reverb implementation, and will then prob do something custom for kandria.

20:07:02 SAL9000 aha, so APF basically rotates the phase of the signal w/o changing the amplitude

20:07:09 shinmera ye

20:07:13 SAL9000 makes sense now :-)

20:07:44 shinmera kinda. I'm still struggling to get my head around the concept of 'phase' for PCM.