All pass delay
Hi all, I’m having trouble figuring out how to configure an all pass delay as is used as a diffuser in many reverbs. Our all pass filter has no time delay.
I’ve done this to approximate the all pass delays diagrams I’ve seen here and elsewhere : https://valhalladsp.com/2011/01/21/reverbs-diffusion-allpass-delays-and-metallic-artifacts
part of the issue - I don’t really know how it’s supposed to sound :) it kind of sounds like a regular delay, but less comby.
Would this be a good DSP module?
Comments
hm, so its a short delay with a lot of feedback and some phase mess
since it says "diffusion" it can't be anything to drastic sounding (a little softer and thats it?)
algo reverb is a lot of voodoo and hard to get "right" ^^
I would look for some simpler model that only talks about that
the reverby stuff is very confusing
@bcrichards wrote:
^ Hi all, I’m having trouble figuring out how to configure an all pass delay as is used as a diffuser in many reverbs. Our all pass filter has no time delay.
Indeed, the All Pass filter has no adjustable delay.
I think the problem here is that you would have to chain more APFs to get a noticeable effect.
Also, the linear delay of the feedback module is already quite high and has a major effect on short delays in the feedback loop, more of it with longer audio buffer settings.
Here's a project of mine showing 3 different reverberators:
T1 using delays only
T2 using APF and feedback
T3 using the built-in FDN reverberator
Would this be a good DSP module?
for reverb?
no
compare track 1,2,3 and use the convolver on track 3
ill pick the convolver anytime over any of this. :)
I’m aware we have a plethora of reverb tools on iOS and I quite like the FDN and reverbs in Drambo already. if we didn’t like to tinker and build, we wouldn’t be using Drambo.
Thanks @rs2000
So the all pass filters need to be chained together to result in noticeable dispersion of sound, got it.
A 12 dB/8va (2nd order) filter should have phase shift starting from 0 a decade below the break frequency to 180° a decade above, with exactly 90° at the break frequency. So setting the break frequency in the middle of the music range should produce some useful dispersion. Is that what you are seeing?
Although, I’m experimenting with a filter bank set up. Offsetting the delay time of the different bandpass filters is sort of like an all pass in that all frequencies pass through, but at different times.
im not really going for audio quality here…just seeing what all goes in to making a reverb for fun.
u want the high frequencies to decay faster than the rest ...
and I guess u want to switch left and right
if you are standing at the left side of the room the reverb is supposed to echo back from the right side?
and some kind of crosstalk between the channels
and you want two sections the early reflections and the following cloud
reverb is really complex
I guess you won't come much further than the "tin can" rs2000 offered.
real reverb looks like this
Not exactly all pass but definitely a strategy on its own.
That's what I love in Drambo. You have a crazy idea and you can just build it and see what happens. 😊
This topic got me thinking yesterday, and I tried chaining some all passes in the delay rack. Well, about 40 APFs. It sounded pretty nice on the percussion I tested it with. Definitely metallic, but much more of a reverberant flavor than a delay. Delay time was 10ms, with mid feedback.
APF cutoff and resonance were set randomly, but all mapped to 2 morph modulators. I would describe the sound as ‘oil can’ or ‘metal barrel’ reverb. Lower general cutoffs seemed to increase the perceived ‘room size’, and higher cutoffs tightened it up. Recorded a video with plans to upload, but forgot. I’ll share when I’m off work.
what I’m curious is about feeding back separate delay lines through all pass chains
Mixing delay lines with different delay times and APF chains with different settings will definitely help smoothen out the reverberation.
I've used 4 chains in my example but only the CPU is the limit 😇
From my reading, these all pass diffusers are just the first component of most reverb algorithms. They’d be fed into longer delay lines after the fact.
there also seems to be chorus involved (modulated delay lines) ...
does not make it sound "real"
but does that "pop music" thing