[sdiy] Weird hobby of the week: BBDs

[anthony]

> Harry obviously has a good point - BBD's are noisy.  You just can't throw
> one in a circuit and expect good results.  Effective low pass filtering is
> an absolute must.  Pre-emphasis and de-emphasis help, and in 99% of all
> cases, if there is no compansion or (shudder) gating, you're still going 
> to
> have a fairly noisy device.  The exception would probably be very high 
> clock

People should really try the LM1894 'Dynamic Noise Reduction' circuit from 
National. I was happy to see that these are still in production (albeit only 
in SMD form). It really does a great job of gating the noise and it does it 
by basically being a low-pass filter with an envelope follower. This is a 
simplification but it's pretty much how it works. It has a gilbert cell as 
its core. Check out the datasheet. I've used them with very good results for 
reverb/stereo expansion.

I should point out that these were BBD's with a relatively small number of 
steps: 128 and 1024.
The noise gets worse and worse as they get bigger, but an MN3006 has a S/N 
ratio of 90 while the MN3007 is 80.
That's not /that/ bad.

I've been wanting to try LM1894 stages in series - this is said to give even 
better noise control. What's cool about it is that it doesn't need an 
expandor at the other end. I predict that results will get less and less 
satisfactory the more BBD stages you add.

But a good point was made that BBD's are best used for flangers and chorus. 
It is indeed hard to beat a digital delay for regular reverb and echo. Tape 
and spring units have their own fun character too.

I think in the end I'll just be using little DSP's.

I really want an AdrenaLinn.

Someone mentioned a Rockman and that made me think about how much I want the 
Adrenalinn. I think I could make something liek that myself, but I'd need to 
research DSP a little more. But I've checked into it and there's a great 
community out there with a lot of free libraries and such.

I'm not suggesting a mass conversion to DSP, but it sure could help take 
care of some things so one could focus one's efforts on specific things in 
analogue.

> rate, high bandwidth flanging where a compandor would kill the 'grit', if
> that's yer thing.
>
> For the past several months I've been working on a modified clone of the
> Boss Dimension C, little brother to the D.  It uses two BBD's running with

I've been following this very closely actually. Lots of cool ideas in there.
I've seen so many really cool ideas online but I think I'll still end up 
making something up on my own. I have to try some things that maybe haven't 
ever been done. Still this project and the Storm Tide were hugle educational 
for me. Thanks, dudes.

> I'm actually building two of them, and last night at 1:00 AM I finally 
> fired
> up the first set of boards to check the audio.  It sounded horrible - very
> noisy and unpleasantly distorted.  I turned around and there was this 
> tall,

I'm having gremlins with my flanger/chorus test mule myself.

> Come to find out the timing cap of the right channel compressor was not
> connected to ground.  I made that connection, and the thing just 
> sang......

awesome

>> I cringe when i imagine BBD reverb, ouch. much prefer a cheap digital
> reverb
>> compared with BBD. but, to each their own...

PSP makes a free VST plug-in that they cool Pianoverb. It's very very cool.
It's liek a spring reverb except it mimics how a piano soundboard sounds 
with the dampers off and a sound is played nearby. I used to make recordings 
with this when I was a kid. (with my bitchin' now deceased Truetone tube 
reel2reel).
At first I found it of little utility until I messed with the tuning and 
detuning controls. If there's dissonance that you don't want you just twist 
and it hits a sweet spot. Way cool.

> The Rockman reverbs to my ears always sounded pretty decent, though the
> gating to prevent fast transients can be a drag.
>
> The MN3011 appeals to me more as a device for chorus/flanging than as
> reverb.

Now you have /me/ wanting one of those. Even more than an 05. Thanks @=^)

> I've never purchased a BBD with more than 1024 stages (other those already
> in devices, that is).  For longer delays, I rely on the Princeton digital
> chips, but even they can sound like crap without proper filtering and even
> compansion (IMO).  The only BBD's I have that are more than 1024 stages 
> are
> the two MN3011's, and those were *given* to me by a very, very nice 
> person.

Know of any links for a good bare bones delta modulator? There is one that I 
think everybody here probably knows:
http://www.armory.com/~rstevew/Public/SoundSynth/Reverb/ddl.htm

This one is on my list of things to play with. And I even have all of the 
parts. (Well in CMOS. I don't have no 74LS393's, but I do have 
74LS157's...). But not a single part on this thing is even a little bit 
pricey. I have tons of 256K dram chips that should work. I'm still puzzling 
how to add more ram to it. It's probably simple though.

ramblin' on...