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How does Buchla patch storage work?
MUFF WIGGLER Forum Index -> Buchla, EMS & Serge  
Author How does Buchla patch storage work?
intellijel
I was wondering how patch storage and recall works on a Buchla 200e system?

If each pot is analog then how are those voltage values stored and recalled?

I also noticed that the 281e module (the only Buchla module I have ever seen in person) there is a clock and data pin as part of the power harness. I have to assume this is for the patch storage system. What com protocol is it using? I2C?
ex_dead_teenager
have you tried writing B&A to get answers to these questions? Because they're really great questions.

I know that there's a dude who works for B&A on Muff he posts as Divisionbyzero https://www.muffwiggler.com/forum/profile.php?mode=viewprofile&u=942

anyway he's been really great for advice and answering my considerably less technological questions about my system and in a previous post here he's sort of offered himself as a go-to guy for B&A I bet if you pm him you'll get a response.

Hope that helps.
amorphiss
Yeah, the 200e uses an i2c bus for patch storage and internal communication (midi note messages etc.). Two pins is all you need for i2c - one for serial data, one for serial clock.
prscrptn
The 200e is a firmware based system which is more digital than analogue; see the FAQ from www.buchla.com below.

You refer to the 200e as an analog system. But your oscillators use digital techniques. What gives?

The common meaning of these terms (analog vs. digital) stems from historical association between user environment and supportive circuitry.

An analog synthesizer is one that uses analog elements, such as knobs and wires, for user interaction.

Now, production costs favor digital circuitry, and the proliferation of samplers demands it. The user interface has become digital for the sake of economy. A single switch can accomplish many functions; multi-level menus, data selectors, and LCDs provide a compact and cheap-to-build facility. These systems do not consider the user interface to be of paramount importance. Parallel access is impossible, alternative interconnection improbable, performance is dependent on MIDI controllers connected with preconceived notions on what each aspect of the controller should accomplish.

Now things have changed. It costs practically nothing to convert between digital and analog respresentations. The designer can provide the user with whatever interface he likes, and proceed to design circuitry that efficiently implements the desired functionality. The user need never know the circuit design, and should not be able to readily discern its premises.

We define the 200e synthesizer as analog. By that, we are describing the aspect that the user contacts as analog. The underlying circuitry is a hybrid mix, constantly flowing from one domain to the other - not even predictable from one module to the next - always designed for uncompromising performance - never for adherence to a design style.

For those who can benefit from further discussion, we shall present some of the design considerations that were used in designing circuitry for a few of the 200e modules. First, we'll consider the 225e MIDI Interface. This gadget has a single digital input (MIDI) located on the back of the system. On the front you'll find 20 analog signals, decoded with 20 digital to analog decoders (DACs). Inside the box are velocity conversion tables (digital) polyphonic logic (digital), assignment directories (digital), and other logic, all tasks best performed digitally. Outside the box - it's strictly an analog world.

Next we'll look at the 261e Complex Waveform Generator. The 261e's user environment is again analog. But much of the internal circuitry is digital. Why digital? For two very significant reasons:

1. The timbre demands are extraordinary. We want to vary timbre in multi-dimensional ways that would be completely impossible with analog circuitry.

2. Requirements for stability and accuracy far exceed what can be accomplished with analog circuitry. This results from a desire to use micro-tunable scales, as well as the demands imposed by the implementation of polyphony.

Since there are no compelling reasons to employ analog circuitry in the oscillators, we went mostly digital, converting from analog to digital in the control section, back to analog in the sync section, back to digital for wave shaping, and converting to analog in the final output section. Again, presenting a 100% analog environment to the user. All in all, performing 15 analog to digital and 4 digital to analog conversions, in just this one module.

Let's look at one additional module, the 292e Quad Dynamics Manager. This one has compelling reasons for digital control paths and analog signal paths. Digital control paths because of the necessity for patch storage and retrieval; analog signal paths for the following two reasons:

1. The enormous dynamic range and extremely low distortion that characterize this module demand specialized analog circuitry.

2. The peculiar non-linear combination of lowpass and amplitude functions also calls for analog circuitry. A digital implementation would have been possible, but far more complex and demonstrating no advantage.

The design approach used in the 292e is similar to that used in several of the 200e series modules. We employ digital techniques for control structures because of the ease of storing and retrieving presets; we use analog techniques in signal chains for optimal dynamic range and to satisfy various perceptual requirements. And, importantly, the user encounters an analog environment.
infinite7
prscrptn wrote:
The design approach used in the 292e is similar to that used in several of the 200e series modules. We employ digital techniques for control structures because of the ease of storing and retrieving presets; we use analog techniques in signal chains for optimal dynamic range and to satisfy various perceptual requirements. And, importantly, the user encounters an analog environment.


maybe it should've been completely digital as it bleeds audio like a haemophiliac. don did tell me they're aware and that there is a new "quieter" version being released soon.
bar|none
@prscrptn

Super interesting, thanks for posting.

Doesn't sound like Buchla is stuck in the past at all, but quite the opposite. At the cutting edge actually.
dougcl
infinite7 wrote:

maybe it should've been completely digital as it bleeds audio like a haemophiliac. don did tell me they're aware and that there is a new "quieter" version being released soon.



Yeah but that bleed through the vactrols is also what makes them ring. You can use the 291e as a VCA, or use two channels of the 292e to control it.
infinite7
dougcl wrote:
Yeah but that bleed through the vactrols is also what makes them ring. You can use the 291e as a VCA, or use two channels of the 292e to control it.


if it was just through individual channels i could understand, but it's cross bleed between channels.
dougcl
infinite7 wrote:


if it was just through individual channels i could understand, but it's cross bleed between channels.


Ah, I see. I haven't witnessed that.
divisionbyzero
intellijel wrote:
I was wondering how patch storage and recall works on a Buchla 200e system?

If each pot is analog then how are those voltage values stored and recalled?

I also noticed that the 281e module (the only Buchla module I have ever seen in person) there is a clock and data pin as part of the power harness. I have to assume this is for the patch storage system. What com protocol is it using? I2C?


the basic flow is knob -> adc -> cpu -> dac. when you save a preset the cpu stores its current value so that it can be recalled later.

when you load up a preset the knobs probably aren't going to be in the same physical location. the cpu scales the knob input such that turning left or right still changes the given parameter in the same direction; once you cross over the stored point the physical knob takes over. this is why you'll see someone used to a 200e flick a knob all the way to the left and then all the way to the right; this guarantees the knob is directly controlling the given parameter.

it sounds complicated but it makes sense when you use it.

also, i2c is used on the internal bus (the power boards are labeled so you can see what each pin does). t's how the modules do those special 200e things that they do.

and for any budding designer out there: i2c is a "communications protocol" the same way ethernet is. it provides you with very little and expects you to implement quite a lot on your own. at least with ethernet you can get reference implementations of ip, tcp/udp/icmp, etc.
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