DAS griesverb.

[the19thbear]

Do any of you know about the DAS griesverb? I left the scope platform a while ago and I really miss this reverb.(that and DAS free tape plugin) I used it mainly (griesverb)for endless feedback sound - I would love to find out if it's modeled after some special hw reverb or at least what the technology behind it is.
It seems that it's a reverb with 3 filters in a feedback path.
Anybody out there have any info?
I have contacted DAS a couple of times but I haven't got any replies.

[jhulk]

i take it is based on a bbd delay reverb

as they use 3 filters as anti aliasing and reconstruction filter the 3 filters make make up a 8pole filter

the frequency range of the bbd is not that high and with the feedback circuits its easy to go over niquist

so they used the 3 filters to remove any frequencies above nyquist from entering via the feedback path

the same filters are used on the chorus units

the eminent310 had it set to 12khz and uses 3 185 fet switches bbd chips

the 185 fet switchs have alternate control inputs that are controlled by a pulse wave and each clock signal is 180 phase to each other

and by setting the clocks to different settings causes the fets to open and close at different rates causing cascading variation in delay

in reverbs the cascade bbd chips to get longer reverbs

tda350 of the eminent310 and solina has a 12ms of delay

the tda1022 has 512 stages of switches and has longer delays by adding them in series and keeping the same clock signals loner delay times can be created

flangers and chorus units

like the juno60 and solina use parallel bbd but out of phase but phase locked

and the signal is then feed back to each other mixed with the original signal in a 0 120 240 phases which creates that big chorus sound

for those types of sound you will need to look for analog reverbs some of the older lexicon

new items using 1 sharc chip based on the same type circuits modeled is http://www.strymon.net/

im currently designing the eminent/solina bbd 3stage chorus

and the juno60 2 stage chorus that uses 2 separate bbd chorus units as chorus 1 and 2 or both chorus 2 is out of phase to chorus 1 and has a faster modulation than chorus 1 chorus 1 is 120 phase to the incoming audio the 3 signals are then mixed together via a sub mixer depending on the switches 1/2/1&2/none different sounds with the fx can be created

these are mono fx

there have been stereo versions made but they are just mono then they take the output of the first bbd and take it to a left sub mixer with original signal then the second bbd goes to the left sum mixer and the right sum mixer then the third bbd goes to the right with the original signal

you then get a stereo version but thats not how the true solina acts

to do a true stereo version as its a 3stage plus original signal mono effect you need 6 bbd chips and a inverting opamp for the input signal

so the right output is inverted to the left output then each channel 3stage bbd uses the same clock sources

the 3 filter anti aliasing circuits are 1 after the output before summing this is on all bbd outputs this acts as a reconstruction filter this is a 3pole sallen key lowpass removing anything above nyquist go out the audio outs then the feed back loop theirs a 3pole sallenkey lowpass filter and on then this gets summed with the incoming audio and goes to a 2pole lowpass filter set to around 12khz then its output goes to all bbd inputs

the feedback path only comes from the first bbd

i have built a few of these hardware units 2 solina types one with tube clipping circuits for adding extra harmonics

and a loganstring mellodyII which uses ther same 3 stage bbd design byt has 2 differenrt modulation sources running at the same time one set of clocks have a 0.6hz clock and the other has a 6hz clock which create a very modulated chorus as the alternating fet switches are modulated by 0.6hz and 6hz

[jksuperstar]

Sounds like a fun project for Mod IV using the BBD module

[jhulk]

very easy

i already built it using that module but also created it using mod delay modules cascaded like a bbd and the created the 2 clock signals 180 out of phase for control

then they are controlled by the phase clock signals which control there frequency

then theirs a master clock whos frequency controls the phase lock signals so all lfo clocks are phase locked to master clock

then the phase clock signals who have there frequency controlled by master clock then there ouput waveforms are set to 0 phase 120 phase and 240 phase

the master clock has a 6db lowpass filter that alters the phase this altered phase adds another 120 phase

so that the original signal will be 0 phase the first bbd will be 120 the next will be 240 and the last bbd will be 360 which is a complete circle

on the solina the chorus clock is set to 0.6hz and theirs a tremelo setting so the master clock master frequency is switched between these settings

but yes you could do it with the modIV bbd module

[David]

Amazing, Jhulk, your descriptions are so clear, like a mini tutorial. Building this modular now. Thnx

[jhulk]

im a synth tech and i design circuits

so everything i do i do it based on circuit design and how i would do it if creating the actual electronic signal

i have created it and ill send it to sharc so it can be a bc modular module

its also great as the clm module allows you to try ideas and if they are keepers then save as preset

its also good for beta testing as you can just add and rtemove modules until you get it how you like

and with the new guidsk you can create stuff not available by the scope atoms

you can create a .dll file and get to use things like convolution and other host type fx with scope

if you need any help let me know

[David]

thanks, thats a great offer
looking over the bcmodular stuff now too

[the19thbear]

Hi. Thanks a lot for the detailed explanation. I don't think it sounds at all like a bbd though. There is plenty of hi freq and nothing grainy in the reverb. I have a bbd that does reverb (also chorus and delay of course) and the sound is not similar at all.
Bu thanks still:)

[the19thbear]

anyone?