The Yamaha DX7 synthesizer's clever exponential circuit, reverse-enginee

November 30, 2021 8:25 PM

The Yamaha DX7 synthesizer's clever exponential circuit, reverse-engineered [Ken Shirriff's blog] "The Yamaha DX7 digital synthesizer was released in 1983 and became extremely popular, defining the sound of 1980s pop music. [technical chip information] In this blog post, I examine this circuit—implemented by a ROM, shifter, and other circuitry—in detail and extract the ROM's data."

Includes an astounding microscopic photo of the chipset that can be blown up big enough to see individual transistors.

posted by hippybear (30 comments total)

I understood just enough of that to find it utterly fascinating . . . and I still wish my dad had let me buy a DX7!
posted by pt68 at 9:05 PM on November 30, 2021 [1 favorite]

That's pretty interesting. I was always curious about how that chip actually worked. The engineers at Yamaha pulled off a remarkable feat with this machine, being capable of making a class of sounds that no other synthesizer could make, with polyphony and a velocity sensitive/aftertouch capable keyboard in a sleek and not too outrageously priced package. The downside was that brilliant engineering was almost never really exploited by users, as it seemed there were only about three people who ever really figured out how to program the thing, and as such, the DX7 was kind of treated like a classy Casiotone preset machine by most owners. But what presets they were, kind of becoming the sound of the 1980s.
posted by 2N2222 at 9:59 PM on November 30, 2021 [6 favorites]

Worth noting that FM synthesis is undergoing a new renaissance, with a wide variety of new synthesizers like the Kong OpSix, MegaFM, and DigiTone reintroducing this methodology in a slightly more accessible format. Or you could just get a Volca FM and load the old DX presets…
posted by q*ben at 10:19 PM on November 30, 2021 [8 favorites]

Heh I just sold the DX7S I bought abt 20 years ago.

Great instrument and I did manage to create one patch using the keyboard’s interface and it sounded so harsh and weird it scared me off.

These days there is a great online editor that you can create patches with and load into your dx7 via midi. Much easier and better results.
posted by awfurby at 11:07 PM on November 30, 2021 [2 favorites]

I have heard that DX7s are hard to find, because Trent Reznor bought them all for use as smashable MIDI controllers on stage
posted by thelonius at 2:43 AM on December 1, 2021 [5 favorites]

The downside was that brilliant engineering was almost never really exploited by users, as it seemed there were only about three people who ever really figured out how to program the thing

I've seen diagrams of what you had to do to program the DX7 and… woof. It's not surprising that very few people went to the trouble.
posted by grouse at 5:55 AM on December 1, 2021 [1 favorite]

and I still wish my dad had let me buy a DX7

My Dad let me buy a DX-7 and I almost immediately began lusting after the Ensonique Mirage because I was (and am) an idiot and sampling seemed cooler.

What I should have wanted was a Prophet-5.
posted by The Bellman at 6:01 AM on December 1, 2021 [1 favorite]

I have heard that DX7s are hard to find, because Trent Reznor bought them all for use as smashable MIDI controllers on stage

Huh. He had accomplices too.
posted by credulous at 6:29 AM on December 1, 2021 [5 favorites]

If you can't find a physical DX7, there's an open-source software implementation that's compatible with DX7 patches.
posted by acb at 6:56 AM on December 1, 2021 [7 favorites]

→ ... an open-source software implementation

Based on code by Raph Levien, who could quite safely be called a polymath.
posted by scruss at 7:37 AM on December 1, 2021 [2 favorites]

Polymath class is hard!
posted by thelonius at 7:48 AM on December 1, 2021 [1 favorite]

Polymath class is hard!

Each equation requires more than one person to solve it, and each step requires the informed consent of all solvers involved.
posted by otherchaz at 8:22 AM on December 1, 2021 [5 favorites]

The story goes that this synth funded the Stanford electronic music department thanks to royalties from Yamaha as FM synthesis was invented there.
posted by njohnson23 at 8:44 AM on December 1, 2021 [4 favorites]

I'm madly in love with my Korg Volca FM. It's complicated to program, but not ridiculously so; my Roland D-05 gives it a run for its money. But man, the sounds this thing can come up with are amazing. It's ridiculously fun to mess around on.
posted by MrVisible at 8:49 AM on December 1, 2021 [2 favorites]

Anybody who is FM-curious should remember that Dexed, a fairly accurate emulation of the DX7 family, is free. Although it’s probably still not the absolute most intuitive FM synth interface, because it has the weird backwards envelope programming.

Really I think FM makes more sense via a modern plugin GUI. It’s a little surprising to me that I still don’t think I’ve really seen the UI done better than NI’s FM8, which is over a decade old. Or then there’s one of my personal favorite synths, U-He Bazille, which is a mostly-modular “drawing patch cables” type UI but with a sound engine and feature set oriented towards phase-modulation-style FM and phase distortion (a related paradigm developed by Casio for its inexpensive 80s digital synths that offered a more similar programming interface to subtractive synths).
posted by atoxyl at 9:05 AM on December 1, 2021 [1 favorite]

Whoops missed that Dexed was already posted!
posted by atoxyl at 9:13 AM on December 1, 2021

Speaking of Stanford, John Chowning (father of FM synthesis) gave a talk at the U of Washington when I was a student. He played a demonstration of FM formants (voice-like sounds) and the way a metallic chord transformed into individual voices singing in harmony was absolutely magical. Afterward, I had the pleasure of sitting him in front of my very simple FM synthesizer running on a DSP chip, on which he created a little "patch." I felt like Frederick the Great inviting Johann Sebastian Bach to try out his fortepiano (lol). It's one of my favorite memories from grad school.
posted by mpark at 9:18 AM on December 1, 2021 [14 favorites]

I briefly owned a DX7. An old friend gave it to me for free back in the mid 90s, back when you could still find keyboards and synths like this at flea markets for pocket change.

Due to instability in my life I never had a chance to really explore it or use it, much less get into the programming of custom patches. I ended up handing it off to someone else at no cost because they helped me move and other instability issues. This post is timely because I was thinking about that synth a few days ago and wondering what happened to it and where it ended up, and if the person I gave it to ever did anything cool with it.

I did get a chance to explore the presets and mess around enough to discover that there was a whole lot of pop music that heavily relied on presets from notable synths like the DX7, everything from major chart topping hits to more obscure 80s synth bands. People won Grammy awards with synths like the DX7.

I've had a lot of vintage music and music related hardware pass through my hands over the years. I spent a couple of years scouring flea markets with a friend who was absolutely dedicated and driven to be one of the first people out there in the early hours of the mornings, and watched him pick up a little of everything from Casio SK-1 sampling keyboards to Moogs, Junos, Jupiters and even Optigons and Mellotrons.

There was a sweet spot in history where you could easily and reliably pick up old music hardware like this for ridiculously cheap prices. We were able to buy some of these notable synths for eye-wateringly low prices like a couple of dollars. He was picking up Moogs, Rolands and Yamahas for like 1-5 dollars. I used to have a small stack of the Casio sampling mini keyboards that I paid no more than 1-2 dollars for. I think he scored the Optigon and Mellotron for like ten bucks, but those electromechanical devices needed a ton of work to get going.

The Optigon and Mellotron in particular were fun because you could make your own "samples" by drawing waveforms on a sheet of acetate (Optigon) or recording samples to strips of audio tape to install (Mellotron) and it was a really interesting and directly hands on process that just made intuitive sense and offered some really interesting opportunities to hack it and creatively break those devices.

It's a weird sort of gentle sore spot for me but in hindsight if I had more stability in my life and I could have kept even half of the weird vintage hardware I used to have at various points in my life I could have built a pretty awesome recording studio. Or waited a decade or two to sell them for enough cash to make a sizeable down payment on a house or some land somewhere.

Another small but gentle sore spot in hindsight is not really understanding how various kinds of synthesis worked back then and I wish I spent more time learning and doing homework about it instead of partying and mashing random buttons. Even additive or subtractive ADSR analog synths were hard to understand and counter-intuitive even though I had plenty of friends into electronic music who did know something about it and I had a fair amount of access to play around with some notable analog and digital synthesizers,

The jargon and glossary of synthesis terms is utterly bewildering sometimes. What the fuck is an envelope? What's a filter? What's a filter sweep? What does parameter mean? Patch? Why is it called a patch, what is it fixing and why? (Because modular synths and "patch bays" of cables!) The fuck is ring modulation? What the heck is a mixer or mixing in terms of oscillators in a synth and why does it not seem to behave like an audio or DJ mixer? Why square waves?

I didn't start to put these parts together until long after software synths and DAWs became popular and you could often visually see what was going on as you tweaked all of those weird knobs and buttons in the UI and get instant visual and audible feedback in the form of waveform displays and sound combined.

But today I'm pretty well versed in ADSR sound design and it's nice to be able to have some idea of what I'm doing with mixing oscillators and messing around with ADSR envelopes. It's really satisfying to be able to walk up to almost any 3-4 oscillator ADSR synth with a sound I want in mind and be able to dial in sound that's really close to what I had in mind.

The DX7 makes that kind of analog ADSR sound design look easy. I remember combing through the programming section of the DX7 manual and being so totally bewildered that it made me so frustrated that it got emotional. That level of FM synthesis is totally insane and convoluted. It's like trying to think in Reverse Polish Notation all the time or something and feels totally backwards and mutant compared to ADSR analog synths.
posted by loquacious at 9:40 AM on December 1, 2021 [3 favorites]

I still don't know what ring modulation actually does. But the ecosystem for understanding how synths work is like a million times better these days.

I work with bird ecologists a lot, and one of them mentioned that in the late 80's early 90's when they were doing their PHD, getting a spectrogram required expensive, specialized hardware that printed out the spectrogram on paper. There probably were some programmatic ways to do it at the time, but they were also specialized and a bit obscure. these days your phone can show you spectrograms trivially, and there are plenty of youtube videos to explain what they are and the many variations...
posted by kaibutsu at 9:45 AM on December 1, 2021

I have heard that DX7s are hard to find, because Trent Reznor bought them all for use as smashable MIDI controllers on stage

I was hoping that was a joke but it looks like it's not. How sad.
posted by grouse at 9:57 AM on December 1, 2021

Some of the later cheap Yamaha FM synths sounded pretty cheesy (the chip was also used in the Sega consoles) but you could program them and get a taste for simple FM synthesis. It was fun to overdrive the modulation and get a broken tone that devolves into white noise.
posted by credulous at 10:02 AM on December 1, 2021

Some of the later cheap Yamaha FM synths sounded pretty cheesy

They cut down the number of operators to cut costs; the results ended up in the chips in AdLib sound cards, among other places, and were more limited in what could be done with them.
posted by acb at 10:12 AM on December 1, 2021

The DX7 makes that kind of analog ADSR sound design look easy. I remember combing through the programming section of the DX7 manual and being so totally bewildered that it made me so frustrated that it got emotional. That level of FM synthesis is totally insane and convoluted. It's like trying to think in Reverse Polish Notation all the time or something and feels totally backwards and mutant compared to ADSR analog synths.

The DX7 was hard on several levels, I think. Even with a modern GUI, FM is fundamentally trickier to program than subtractive because of the complicated way modulators can interact. There’s sort of an entry-level understanding of sine FM that’s pretty accessible - odd ratio gives saw-like harmonics, even ratio gives square-like harmonics - and then a whole mathematical theory to getting exact results. I love the sound of FM but I mostly program on that intuitive level with a layer of experimentalism on top making things weirder and noisier, which is why I like Bazille. And then on top of that the DX7 (and the whole family of Yamaha FM chips) is a weird outlier in the way it approaches some basic stuff like envelopes. And then on top of that, it inaugurated the era of no or few knobs (unless you shelled out for the programmer) on the synth. I guess because they just figured few people would even want to try to program it.
posted by atoxyl at 11:26 AM on December 1, 2021 [1 favorite]

The Casio phase distortion synths (which have a few software emulations or successors, now) are actually a pretty clever design. It’s a digital engine - could be considered a very special case of FM, I think, but don’t quote me on that - which allowed them to make very cheap polysynths. But the programming model is much closer to “subtractive in reverse” - starting with a sine wave and adding harmonics until it turns into a saw or a square - than Yamaha FM offers.
posted by atoxyl at 11:36 AM on December 1, 2021 [2 favorites]

I guess because they just figured few people would even want to try to program it.

They were right. e.g. "What's Love Got To Do With It" uses at least three default DX7 patches.
posted by credulous at 12:16 PM on December 1, 2021 [3 favorites]

There was a sweet spot in history where you could easily and reliably pick up old music hardware like this for ridiculously cheap prices.

This is what Roger Joseph Manning Jr. did after Jellyfish broke up.
posted by thelonius at 12:31 PM on December 1, 2021

→ There was a sweet spot in history where you could easily and reliably pick up old music hardware like this for ridiculously cheap prices.

I wonder if it's on the same sort of time cycle as my elderly New York "folk scare" friends would describe going around junk shops and church sales in the early 1960s and picking up now rare and classic acoustic instruments. One of them still plays the early 1900s Fairbanks Special Electric banjo (which isn't electric at all, but would set you back about $5k if you could find one) which he got for $2. Another ruefully remembers the mid-1920s Gibson F-5 mandolin he got among junk he and a friend got paid a buck each to clear out of a church basement, which he then traded for a wrap of speed. An F-5 in good condition today can be worth north of $100k.
posted by scruss at 1:47 PM on December 1, 2021 [2 favorites]

Pawnbrokers used to have no idea what old guitars were worth, they took quite a beating for years.
posted by thelonius at 2:12 PM on December 1, 2021

What I should have wanted was a Prophet-5.

Ah, the vintage gear lottery. I know someone who bought an old Minimoog for $100 back when DX7s were popular. I gave away/lost a Boss CE-1. I still have a few fine old things, but they're not market desirable.

loquacious says what I sometimes feel;

Another small but gentle sore spot in hindsight is not really understanding how various kinds of synthesis worked back then and I wish I spent more time learning and doing homework about it instead of partying and mashing random buttons...

sounds like Synth Britannia?
posted by ovvl at 6:54 PM on December 1, 2021 [1 favorite]

I feel like I want a giant blow-up of that microscopic chip photo framed on a wall. It's really elegant and beautiful.
posted by hippybear at 10:53 AM on December 4, 2021