Stereo effects in general + overload delay ram

[isak]

Hi guys,

first post after reading and trying few approaches with the spinCAD and bumped into 'delay ram used' is full trying to make stereo shimmer reverb and i have few questions please.
how is it possible to make real stereo in and stereo out if i open 2 reverbs units and i get 'delay ram used' is full?
are there any differences between the working in spinCAD and working with spinASM overloading the ram etc?
maybe my approach is not good trying to open 2 reverbs units to get real stereo?
i must add that my code abilities are non, i was naive thinking i could get away with code wirting and make everything with the spinCAD.
dont get me wrong here, the spinCAD is great for general and cool effects, even complex ones, but i get this feeling that if i want to get the max out of the VF-1 i need to use spinASM, yet again, how about the RAM issue, will it happen to me in spinASM as well for doing 2 reverb units to get real stereo shimmer?

thank you for taking the time to read my post.
Isak.

[ice-nine]

For Stereo Reverbs you could have a look at the reverbs in the 'Free DSP programs' section on the SpinSemi website, there are some stereo reverbs by 'Harmon Grold' to download and try. If this is the type of thing you are looking for you can use the code and optimise it to what you would prefer for your project. The best way to write your effects is obviously by learning how to edit the code yourself but it is a big learning curve and the examples are the best way to experiment with ideas.

[Digital Larry]

There should be at least one stereo reverb in SpinCAD (two outputs on the bottom of the block). All the reverb code in SpinCAD is taken from the Spin programs, either "Free DSP" or this forum, or the OEM projects code samples. Only the "small reverb" IIRC is small enough to have two simultaneously and since it's the same algorithm you're not buying much there. There is one reverb block that lets you "scale" it in size, which reduces all the delay line lengths down by the same amount. You might try that one and scale it down all the way or until you can get two to fit, if you're set on having two completely independent reverbs. If there's a setting for the number of delay lines, reduce that to 2.

Stereo reverbs in the Spin collection work by taking taps from different places in the delay lines, of a single reverb structure. All the ones I ever saw were mono in or mix stereo in to mono. So to create the stereo out, there is at the very least a fixed time displacement between any two single taps, as the delay lines are formed into a ring structure, the end of which feeds back to the input of the ring. Sprinkle a few taps around the ring and mix and match them for your stereo outs. This is also known as "Digital Larry's Shoot in the Dark" method for designing FV-1 reverbs. If somebody's got a better one I'd be interested to learn it.

SpinCAD Designer is not a great tool for designing different reverbs in all honesty.

DL

[isak]

Hi Guys.

thank you for your comments
I actually found a way to make the shimmer reverb stereo, i'm very happy with the results.
now i'm trying to make the reverb longer, much much longer tail with the same shimmer reverb i did.
so i thought to make another feedback from the reverb output to a 4 to 1 mixer the chain is..
input 1 and 2 goes to the input 1 and 2 of the 4 to 1 mixer.
input 3 of the 4 to 1 mixer is for the shimmer reverb output to feedback and in parallel connection to the main output.
input 4 of the 4 to 1 mixer for the second feedback from reverb output to feedback and in parallel to the main output.
this works well and i do get longer reverb, but i get this tones, some kind of metallic sound when i do that, the moment i disconnect the second feedback (not the shimmer feedback) the tones are gone but i dont get longer reverb.
i did used hipass filter not to get the feedback haaaaam sound it works but yet again i get those metallic tones.
any idea how to make it longer?
in general i think the spinCAD is great tool for non code writers to experiment with.

best,
Isak.

[Digital Larry]

this works well and i do get longer reverb, but i get this tones, some kind of metallic sound when i do that, the moment i disconnect the second feedback (not the shimmer feedback) the tones are gone but i dont get longer reverb.

Welcome to reverb design 101! You'll notice throughout the Spin reverb examples all sorts of "magic" numbers (delay line lengths, all pass coefficients, etc.) with no explanation at all as to how those things were selected other than by trial and error. That's not to say that I expect Spin to teach everyone about this because it's not a simple subject, and the FV-1 was designed in a specific way that leads more directly to certain structures than others.

So, I've been looking at FV-1 reverb code for about 8 years, and I still only understand a couple things about the magic numbers (I think).

Supposedly, there will be fewer resonances in the reverb decay if the lengths of all delay lines are mutually prime. I tried testing this once by using Wolfram Alpha to print out all the prime numbers up to 10,000 as reverb delay lines tend to be in the 2000-4000 sample range mostly. I took a reverb algorithm and set all the delay line times to the closest prime number from the list. I didn't spend a lot of time at it, but my recollection is that it didn't make much difference.

If you turn all your all pass coefficients down to zero, you wind up with something that sounds like a bunch of clear delays. The all passes mostly work by smearing things out in time. There's some magical range but I can't tell you that 0.35 should be used for "plate" or 0.63 should be used for "hall" or whatever. In fact, as you look through all the examples of reverb, you'll find that 90% of them or more bear a structural resemblance to the "Dattoro" reverb. So, which parameters in this structure should be varied how to make a room? A hall? A cathedral? You can look at the examples which are so categorized and try to extract that information from the code, but I have not succeeded in doing this in any useful way.

How do you make an FV-1 reverb less "metallic"? That's a really good question.