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To the MAX: How Cherry Audio Turned the Roland SH-5 Into a Soft Synth
Emulating classic synthesizers for plugins is something of a dark art. We talk to Cherry Audio to find out how they turned the rare Roland SH-5 into their newest plugin, SH-MAX.
Cherry Audio has an astonishing work schedule. Their latest plugin, SH-MAX, is their 37th instrument in eight years. Given the speed with which they crank out soft synths, you’d think Cherry Audio had a massive team or they were at least farming out the work. But no, it’s just a handful of people beavering away, turning rare and much-coveted analog synths into code.
From the outside, this process of converting hardware analog richness into a plugin that you can load in your DAW and play seems more like a dark art than your usual coding. We spoke to Dan Goldstein, Cherry Audio’s Chief Technology Officer and the driving force behind the DSP of the vast majority of the company’s instruments, to find out how they do it, with a special focus on their latest, SH-MAX, a sort of greatest hits of Roland’s 1970s monophonic synths.
Choosing the Right SynthThe emulation process actually starts long before any code gets written. First, the Cherry Audio team has to choose the synthesizer they want to recreate. Although there are a number of things to consider, including customer requests, an important factor is access to the original hardware.
“It's insane. It's massive, the number of synths he has,” says Robert Saint John, Cherry Audio’s Director of Marketing, about the personal collection that Dan has to pull from. “But he doesn't have everything.” If Dan or another member of the team (they’re all synth nuts) doesn’t have the synth at hand, they’ll try to find one, like the Korg PS-3300 they had to visit to measure and record.
In the case of the SH-MAX, they decided to take a slightly different approach and combine the best bits from different models in Roland’s 1970s SH line. “It was a fun change to be able to say, ‘Why don't we take the VCO from the SH-7 and the (additive oscillator from) the SH-3A,’” Dan says. “On the SH-7, you can blend these square waves together like an organ, but on the SH-3A, you can actually choose different waveforms for those octave sliders. We said, ‘Well, it's not part of the SH-5, but let's put it in there anyway. Let's do things like audio rate filter modulation and aftertouch, which isn't part of any of the SH line, and really push it.’ It was fun. Honestly, all of these projects are fun. I love synthesizers.”
[quote align=right text="You really have to love the synthesizers and spending time with them because the majority of the emulation process, it turns out, is just turning knobs"]
Turning KnobsYou really have to love the synthesizers and spending time with them because the majority of the emulation process, it turns out, is just turning knobs. Of course, there’s the art department’s input, and sound design further on down the line, but for Dan, it all comes down to painstakingly recreating the behavior of the target synth.
“What we are trying to do with every one of these is turn every single knob and move every single switch and every single slider and figure out exactly what's happening internally with the circuitry, and measure what it does to the sound, so that we can replicate that,” Dan explains. “It is first and foremost a very tedious and frankly boring process a lot of the time. It is not exciting work.”
He goes on to explain the process further: “It is a lot of moving a knob a little bit and then measuring what it's done to the sound, and then moving it a little more and measuring what it's done, and then ultimately trying to figure out the curve or the shape of the modification to the sound so that we can exactly replicate it.”
It’s a numbers game, with the more effort they put in, the better the emulation turns out to be. “In the end, it's just time-consuming, careful measurements,” he says. “There's no magical secret to it.”
Oscillators and FiltersRoland’s 1970s synthesizers had a very different sound from their later instruments. Big and beefy, these early analog monos were more like American synths than what we would come to expect from the clean and polite Roland of the 1980s. So how did Cherry Audio emulate the monstrous oscillators on the SH-5?
“In the case of the SH-5, there's really nothing unique about its oscillators,” says Dan. “Surprisingly, with most analog synthesizers, the oscillators themselves in isolation are generally the same. They're made by charging a capacitor. They charge and discharge and the shapes of the raw oscillators don't tend to differ that much.” The SH-5 does have some special features in the oscillator section, like ring modulation and two types of oscillator sync, which Dan was careful to emulate, but ultimately the sound of the synth isn’t just the oscillators. Says Dan: “It comes from the oscillators through those filters.”
Unusually, the SH-5 has two filter circuits: a multimode with lowpass, highpass and bandpass, and then a second bandpass filter with its own circuit. “It's a different kind of filter with a different filter shape than the VCF,” Dan explains. “Essentially all four of these filters have to be modeled and they all contribute to the sound of this instrument.”
They’re also very aggressive. “When you crank that resonance up, that resonance is really loud and surprisingly distorted,” he says. “It overdrives. The resonance itself gets clipped. It can be beautiful.”
Modifying the ModulationAnother key element to the overall sound of a synthesizer is the shape of its envelopes. The rate at which amplitude and filter envelopes rise and fall is different from instrument to instrument - and entirely dependent on the internal circuitry.
[quote align=right text="A synth's envelope shapes can have a major impact on the sound and feel of the instrument."]
“You get an envelope on a synthesizer by charging a capacitor,” explains Dan. “In most synthesizers, it's a logarithmic shape. It jumps up quickly and then smooths out at the top. Some analog synths have software envelope generators, and those are usually linear, just a straight line. The SH-5's attack is exponential. It starts off slow and then rises quickly.”
This gives the SH-5 a very different feel. This is especially noticeable when you're playing a pad or string sound. “You hit a note and it slowly fades in and then roars to life,” says Dan. “Even if you're not measuring this, even if you don't have it on a scope and you're not calculating this, it feels different to play it.”
Measuring the HardwareSpeaking of measuring, how is Dan able to recreate these curves so the software emulation behaves like an analog hardware synth? Is it just great ears?
“No, in the case of the envelopes, there's a few things that have to be measured,” Dan answers. “One is obviously the shape, and then the other with every synthesizer is the time.”
How long does it take to get from the zero point of an attack stage to its greatest volume? What about all the values in between? Dan continues: “Most synthesizers are not linear with their envelope sliders, meaning if the maximum time is 10 seconds, the middle position is not five seconds. It's usually two seconds or something like that. This is part of the tedious process.”
To capture all of this information, Dan makes audio recordings. “I hit a note at the fastest speed, and then I turn it up a little bit, and I hit the same note, and I keep doing that until I have measured the entire range from fastest to slowest, and then I pull it into an audio editor,” he says. “In the audio editor, you can very clearly see the shape of that envelope.”
Of course, Dan also has quite a bit of personal experience to fall back on, both with hardware and software - but he still has to put in the legwork. “The benefit of us doing 37 synthesizers is I can look at what's coming out of a synthesizer and I can have a pretty good idea of what that circuitry is doing. Then I can look at the schematics and verify and confirm that it's working the way I think it is. But no matter how much experience I have, there's still the long, tedious process of just measuring everything. Oscilloscopes, spectrum analyzers, and just recording audio and looking at it, those are the tools of the trade. That's what I spend all my time with.”
Reusing CodeThankfully, having done this a fair few times already, Dan doesn’t have to start from zero at the beginning of a project. He can re-use code and then make adjustments where necessary. For example, with the filter. “I will generally start with a generic digital four-pole state variable filter that matches the circuit that we're emulating,” he says. “Then I will customize it over this long, tedious process to respond and behave to match the hardware.”
This is true of the envelopes as well. “There are things like envelope generators that don't change much between synthesizers,” he points out. “But then for every single instrument, we have to measure the maximum attack, the minimum attack, the maximum release, the minimum release, the curve of that control as you move it, and then transpose what the hardware does and what its limitations are onto that basic capacitor charging and discharging algorithm that we use.”
A Release Is Never FinishedOur last question for Dan is one that most creatives will have struggled with at some point: how do you know when a project is finished?
“It's a good question,” Dan answers. “With the Mercury-8, our Jupiter-8 emulation, I knew we were finished when I could take any sound on the Jupiter-8 and send it to the software and have it sound identical. Likewise, any sound from the software could be sent to the hardware over SysEx. When they sounded the same, that's when I knew that we were done. If you can turn the knobs between the software and the hardware and hit a note and have them sound the same, then I know that we've done it right.”
However, even once they’ve shipped the project, they’re not necessarily finished. There are updates, new ideas to implement, additions. “What’s great about modern software is that we can fix a bug and push the fix out to our customers, and what didn’t work yesterday will work flawlessly today,” Dan says. “It’s one of the things I love about modern software. Our products never have to be done, they can always be fixed and improved, just like a song can be remixed and re-recorded, remastered and re-released.”
For Dan and his team, the work never stops. Even after the hundreds of hours of measuring and comparing, they’re still making tiny changes, even after release. “I’m constantly making minor changes to the filter resonance and overdrive, to more perfectly match what I’m seeing in the hardware. We might not sell more copies because of these tiny changes, but I’ll know that the hardware and software line up perfectly. I suppose that makes us a bit obsessive, but I can’t stress this enough: this is obsessive work.”
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