It's the same basic topology, but some of them take outputs from the delays inside the allpasses (both the input allpass chain and the loop allpasses). So they have a very rapid onset, but sometimes a metallic sound.
Yeah, this caused me some confusion. I have the SDR 1000 and it's fairly obvious that the sub-reverb is a separate mono in/mono out reverb. Plus on the REV5 it's an independent reverb. I was expecting something fancier.
You wouldn't happen to have the SDR 1000+ or MU-R201 ROM dump, would you? Mine's the original model.
The REV5 is a pain in the ass too. 1500ms of delay and only increment/decrement buttons
. You can watch your fingernails grow while holding the button down. It makes the Quadraverb's pressure sensitive buttons seem totally brilliant. And that's just a piezo transducer attached to the back of the PCB. Was everyone else too stupid to just copy that?
That's just my reaction to hearing the impulse response. Impulse responses are a great way evaluate at least some aspects of a reverb, but they also kind of provide too much information. It's really unflattering, like watching porn in 4K. An impulse response might sound nasty with a bunch of allpass ringing, but you probably won't hear it on a musical signal. And anyway I'm overly picky, at least when it comes to things that are supposed to be high end. The Midiverb gets a pass, but I'm gonna criticize everything else to death.
I think version 1 just uses one algorithm, which is basically A but with 2 allpasses per output channel rather than 3. It's not as good, and you're not missing anything if you don't have it.
I noted the panning thing, but I think it's still constant echo density. I would have dug into mine already, but I want to poke around in the hardware first. I need to find the exact sample rate, the number of instructions per sample, etc. And clean the pots and maybe modify it a little.
It's crossed my mind also to acquire a DPS V77. Normally I rule out buying "fancy" gear or spending more than like $100, because I can design stuff that's better (maybe not so much with very good pitch shifters or highly nonlinear VCFs, but almost everything else). But things like the Sony DPS V77, Alesis Quadraverb 2, Roland SRV 330, Dynacord DRP 15, Korg A1 and Behringer V Verb do tempt me, at least if they're cheap enough.
Impulse responses. The guy who wrote
this article (Georg Müller) posted some impulse responses from version 1. I opened them in Audacity and figured it would be relatively easy to reverse engineer since the echo density is quite low. I asked him if he'd be willing to make a couple test recordings. He agreed to do it, but his unit had since been upgraded to version 2. I messed around with Audacity and a couple Matlab scripts, figured out version 1 (minus the initial delay since there's no dry impulse for reference), analyzed some of my own gear, then figured out version 2.
Turns out it's actually pretty easy for most designs, regardless of echo density. There are certainly things that I wouldn't be able to analyze easily, but in practice I haven't encountered them. At this point I expect that most commercial reverbs use variants of Schroeder topologies (other than Lexicon, Quantec, Alesis, Dynacord, Ensoniq, Ursa Major and Eventide). Allpass loops are harder, but doable if the allpass coefficients can be set to 0. I don't have a good way to analyze modulation. Delay lengths are estimated (this mostly depends on how closely the actual sample rate matches the nominal sample rate). Gains are rough approximations. I can determine where filtering happens in the feedback loop, but not really the specifics. That's far from sufficient to make a totally accurate plugin, for example, but it's enough to play with the algorithm, make variations on it, compare different models, etc.
So if you'd like to make me some test recordings...
The right way to do it would be to use a logic analyzer to read the data sent to the DSP, then try to deduce the instruction set as you fiddle with delay times, feedback, filtering, etc. And maybe also see what the RAM addresses are doing, send the DSP different instructions to see what happens, etc. The instruction sets aren't generally going to be very complicated because it's mostly just MAC instructions. But it's still a huge headache. And then there's also mapping the user parameters to the DSP program, etc.
It wasn't that hard with the Midiverb since it's all discrete logic and the instruction set is near trivial. I just needed the schematic, ROM dumps and an oscilloscope. It wouldn't be a big deal to do the same with the Alesis XT and XT:c. But that's not the case for most reverbs.
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