10 ms·

The Design of the Roland Juno Syntheziser's Oscillators

241 points by cushychicken 6y ago

rmcclellan 6y ago
Great article! For those interested in an open source design embodying these techniques, I have an open source hardware design here: https://github.com/russellmcc/dco https://github.com/russellmcc/dco with a blog write-up here: https://www.russellmcc.com/posts/2013-12-01-DCO.html https://www.russellmcc.com/posts/2013-12-01-DCO.html . Also of relevance is an open source hardware design for the later roland alpha juno digital oscillator design: https://github.com/russellmcc/alphaosc https://github.com/russellmcc/alphaosc https://www.russellmcc.com/posts/2019-06-14-Alpha-DCO.html https://www.russellmcc.com/posts/2019-06-14-Alpha-DCO.html
kens 6y ago
Very nice article! The technique of using an op amp with capacitor as an integrator is also a key component of analog computers. By hooking up a few integrators, an analog computer can quickly solve differential equations (in the 1960s, much faster than a digital computer could).
- jeffwass 6y ago
  This is also why op-amps are named that - Operational Amplifiers, they can do many mathematical operations. My college electronics prof was old-school enough who told us back in his day it was “standard practice” to use pp-amps to solve differential equations from their Calc class.
  - hazeii 6y ago
    Prior to moving to PDP-11's and paper-tape, the special-effects company I worked for many years ago used analogue computers stuffed with op-amps to control the motion of camera rigs - i.e. analogue motion control. I never saw one in operation, but apparently a cardinal sin was opening the door when the system was in operation (the temperature change would cause enough error to ruin the shot).
- type0 6y ago
  This is the best article on DCO that I ever seen, so many thanks to the author. Often digital oscillators are unfairly misrepresented and it's difficult to find a fair comparison on the fundamentals of it.
cushychicken 6y ago
Love the animations / illustrations in this. Way nicer to look at than LTSpice.
throw_m239339 6y ago
> The biggest problem with the VCO design is that the control voltage that determines the frequency is generated by a complex circuit that is very sensitive to temperature drift and manufacturing tolerances. This means that the generated control voltage might not match up to exactly to what it should be for the desired note and it'll end up sounding out of tune. What's worse is that even if you adjust for this you'll need to re-adjust as the instrument gets warmer! Instability ironically prized and cherished by synth enthusiasts who will claim it makes old synthesizers sound "better" than modern ones...
- cageface 6y ago
  Synth nerds are among the most ardent gear fetishizers there are. Personally I'm very happy to have my gear finally reduced to a laptop and a set of headphones.
  - tomcam 6y ago
    Cannot upvote this enough. The portability is one thing. Another is reliability. I love Roland and Korg, but I purchased the last two Korg flagships and they both stopped functioning right after the warranty period. They are essentially custom computer hardware with none of the service options or reliability available in the PC/Mac world. Also Korg somehow gets their distinct sounds near flawlessly in software, even though their iPhone apps are a tiny fraction of the price of the hardware in real life.
    - colanderman 6y ago
      > reliability Pre-COVID I had a semi-regular synth jam session with a dude 100% invested in software synths. First 30 minutes (no exaggeration) of every session was him fighting with Ableton or whatever, and rebooting his Mac, trying to get something trivial to work, like MIDI clock or input monitoring. Meanwhile I just plugged my Minilogue into the power strip and mixer and did my own thing. There's something to be said for a musical instrument not to be joined at the hip to a general-purpose networked computing device.
iainctduncan 6y ago
Great article. Thanks for the share, and if Thea reads this, thanks for the article. I look forward to reading it more thoroughly.
- cJ0th 6y ago
  I can only second this. It was surprisingly easy to follow along even though I know very little about electronics (I do program synths, though). The interactive illustrations are also great.
ryanwhitney 6y ago
Highly recommend checking out the WebAudio API[1] for anyone interested in this kind of thing. It’s got some obvious shortcomings and wild browser inconsistencies, but lets you go through much of the same design process in making your own synth. 1] https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_A...
- tomcam 6y ago
  Downvotes are completely unjustified IMHO. Poster did not even express an opinion.
  - FpUser 6y ago
    Downvoting makes me think about bunch of demented hounds chasing after anything that deviates from a party line
  - barryhoodlum 6y ago
    Hacker News does not like JavaScript.
the_local_host 6y ago
Thanks to the author for this. My amateur-hour electronics dream is to level up from simple Arduino/control voltage hacking to an actual, workable polyphonic synthesizer.
- aidos 6y ago
  Ha! Been there. It’s surprisingly tricky (I know lots of software, not so much hardware). It was as great fun to work on though.
- smogcutter 6y ago
  http://musicfromouterspace.com http://musicfromouterspace.com is a great place to start. Going from simple dc arduino inputs to high precision analog is a bear, but super rewarding. Get ready to get your soldering skills right and start caring about resistor tolerances!
  - tazard 6y ago
    WILL attract alien visitations - CAUTION ADVISED WILL DEFINITELY cut into TV viewing time - CAUTION ADVISED Stimulates plant growth and calms goldfish. Well thanks. There goes all my free time... But seriously, that website looks like an amazing resource
  - franky47 6y ago
    I learned electronics from Ray's diagrams, he is truly missed. Another of my synth DIY mentors (with whom I worked on the Arturia MiniBrute) is Yves Usson: http://yusynth.net/index_en.php http://yusynth.net/index_en.php
- petepete 6y ago
  For a little extra inspiration have a look over Look Mum No Computer's projects. He's a little out there but has a deep knowledge and boundless enthusiasm. https://www.lookmumnocomputer.com/projects https://www.lookmumnocomputer.com/projects
  - 6y ago
SeanLuke 6y ago
You'd think that making a fully digital square or sawtooth wave would be trivial compared to this, but in fact it's much, much more difficult because the digital wave must avoid aliasing, an issue the analog wave generator needn't concern itself with.
- Applejinx 6y ago
  Depends on how you approach 'trivial'. I've been hacking on Music Thing Modular Chord Organs for some time: they are a little Eurorack oscillator that can play chords, based on a Teensy. The Teensy audio library determines what waves you can get, and there's a 12 bit DAC built in. You can specify the sampling rate of the Teensy with a bit of fiddling, and the limits depend on what you're asking the audio library to do. The stock Chord Organ's set up to run at 44.1k, using a couple of submixes in the library to do things like set waveform levels independently. You can also set an oscillator to drive the output pin directly, with just one waveform. I've got a couple of 'em running at 2,822,400hz instead of 44,100hz. That's 2,822k for one oscillator (I can get four running at 768k), by telling the Teensy its sample rate is something hilariously high, just to run some square and 12-bit triangle and sawtooth waves. I avoid aliasing pretty well :) and it's definitely a fully digital DAC output. It's just good at being free from aliasing because I'm not concerned about what the sampling rate 'means' in terms of 'usable notes'. The only thing I care about is getting my waves nicer. The Teensy also has a rectangular wave, which is PWM adjustable. That, at 2,822k or even 768k, is quite nice even when it's a really thin pulse… And of course you could use the square to drive an integrator :)
  - TheOtherHobbes 6y ago
    None of this was possible in the early 80s when the Junos were designed. The Cortex M4 in the Teensy runs at 200MHz. In the early 80s consumer-grade DSP didn't exist at all. There were some exotic studio processors with slow microprocessors supported by custom hardware multipliers, but 8MHz 16-bit microprocessors were considered fast, expensive, and exotic. Roland had a stellar run with their hardware designs. The Junos may be one of the best synthesizers ever made hitting the bullseye for price, character, simple but flexible programmability, and a legendary sweet but powerful sound. There's a finesse to this kind of audio design that IMO makes a lot of Eurorack seem clumsy and uninspired in comparison.
pen2l 6y ago
Just want to say that I was caught off-guard by the quality of the article, the text, the media, all of it. Bravo to the author.
barry27 6y ago
This is a great article.
bumbada 6y ago
I love the article. I did electronic music myself in the past, and this is very very good and detailed explanation. It motivates me to try it back. I have to find a little time to do something interesting now that I have the resources that I had not in the past(if only I had the time I had then).
nyanpasu64 6y ago
> The output voltage across the range can vary as much as 1 Volt, but that's fine- your ear won't really be able to tell the difference. If I understand correctly, the output from the sawtooth has a voltage offset? Can that lead to DC passing through speakers? And would the pulse-width comparator input need an equivalent voltage offset?
- theacodes 6y ago
  Yes, all of the waveforms out of the waveshaper have a DC offset. The synthesizer removes that when mixing them and sending them through the filter.
  - nyanpasu64 6y ago
    Did you mean that the amplitude of the sawtooth can change by up to 1 volt (due to imperfections in the differentiator and amplitude compensator)? And if the PWM is based on comparing the sawtooth with a fixed voltage, and the sawtooth amplitude changes with pitch, does the PWM width change with pitch?
    - theacodes 6y ago
      You're correct. The pulse-width of the saw wave is very dependent on the amplitude of the saw, so when there's a 1 volt deficit in the saw wave's amplitude you lose about 8% of the pulse width. It's really not that noticeable in practice, though, and if anything it adds to the sonic character of the juno.
filoeleven 6y ago
If you like the sound of the Juno and don’t want to pay vintage synth prices for one, I highly recommend the Behringer DeepMind. It is clearly modeled after the Juno, and adds a lot of nice features (2 DCOs per voice, 2 more-capable LFOs, an arpeggiator, full FX suite...) and you can get the 12-voice keyboard model for about half of what you’d pay for a Juno 106. It’s got a big screen in the middle, but the front panel is designed so that you almost never have to use it, even when building patches. They have a great shortcut system for assigning modulation that’s easy to pick up and very fast to use. It’s just a great synth all around.

241 points by cushychicken 6y ago

Great article! For those interested in an open source design embodying these techniques, I have an open source hardware design here: https://github.com/russellmcc/dco https://github.com/russellmcc/dco with a blog write-up here: https://www.russellmcc.com/posts/2013-12-01-DCO.html https://www.russellmcc.com/posts/2013-12-01-DCO.html . Also of relevance is an open source hardware design for the later roland alpha juno digital oscillator design: https://github.com/russellmcc/alphaosc https://github.com/russellmcc/alphaosc https://www.russellmcc.com/posts/2019-06-14-Alpha-DCO.html https://www.russellmcc.com/posts/2019-06-14-Alpha-DCO.html

kens 6y ago

Very nice article! The technique of using an op amp with capacitor as an integrator is also a key component of analog computers. By hooking up a few integrators, an analog computer can quickly solve differential equations (in the 1960s, much faster than a digital computer could).

jeffwass 6y ago
This is also why op-amps are named that - Operational Amplifiers, they can do many mathematical operations. My college electronics prof was old-school enough who told us back in his day it was “standard practice” to use pp-amps to solve differential equations from their Calc class.
- hazeii 6y ago
  Prior to moving to PDP-11's and paper-tape, the special-effects company I worked for many years ago used analogue computers stuffed with op-amps to control the motion of camera rigs - i.e. analogue motion control. I never saw one in operation, but apparently a cardinal sin was opening the door when the system was in operation (the temperature change would cause enough error to ruin the shot).
type0 6y ago
This is the best article on DCO that I ever seen, so many thanks to the author. Often digital oscillators are unfairly misrepresented and it's difficult to find a fair comparison on the fundamentals of it.

cushychicken 6y ago

Love the animations / illustrations in this. Way nicer to look at than LTSpice.

throw_m239339 6y ago

> The biggest problem with the VCO design is that the control voltage that determines the frequency is generated by a complex circuit that is very sensitive to temperature drift and manufacturing tolerances. This means that the generated control voltage might not match up to exactly to what it should be for the desired note and it'll end up sounding out of tune. What's worse is that even if you adjust for this you'll need to re-adjust as the instrument gets warmer! Instability ironically prized and cherished by synth enthusiasts who will claim it makes old synthesizers sound "better" than modern ones...

cageface 6y ago
Synth nerds are among the most ardent gear fetishizers there are. Personally I'm very happy to have my gear finally reduced to a laptop and a set of headphones.
- tomcam 6y ago
  Cannot upvote this enough. The portability is one thing. Another is reliability. I love Roland and Korg, but I purchased the last two Korg flagships and they both stopped functioning right after the warranty period. They are essentially custom computer hardware with none of the service options or reliability available in the PC/Mac world. Also Korg somehow gets their distinct sounds near flawlessly in software, even though their iPhone apps are a tiny fraction of the price of the hardware in real life.
  - colanderman 6y ago
    > reliability Pre-COVID I had a semi-regular synth jam session with a dude 100% invested in software synths. First 30 minutes (no exaggeration) of every session was him fighting with Ableton or whatever, and rebooting his Mac, trying to get something trivial to work, like MIDI clock or input monitoring. Meanwhile I just plugged my Minilogue into the power strip and mixer and did my own thing. There's something to be said for a musical instrument not to be joined at the hip to a general-purpose networked computing device.

iainctduncan 6y ago

Great article. Thanks for the share, and if Thea reads this, thanks for the article. I look forward to reading it more thoroughly.

cJ0th 6y ago
I can only second this. It was surprisingly easy to follow along even though I know very little about electronics (I do program synths, though). The interactive illustrations are also great.

ryanwhitney 6y ago

Highly recommend checking out the WebAudio API[1] for anyone interested in this kind of thing. It’s got some obvious shortcomings and wild browser inconsistencies, but lets you go through much of the same design process in making your own synth. 1] https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_A...

tomcam 6y ago
Downvotes are completely unjustified IMHO. Poster did not even express an opinion.
- FpUser 6y ago
  Downvoting makes me think about bunch of demented hounds chasing after anything that deviates from a party line
- barryhoodlum 6y ago
  Hacker News does not like JavaScript.

the_local_host 6y ago

Thanks to the author for this. My amateur-hour electronics dream is to level up from simple Arduino/control voltage hacking to an actual, workable polyphonic synthesizer.

aidos 6y ago
Ha! Been there. It’s surprisingly tricky (I know lots of software, not so much hardware). It was as great fun to work on though.
smogcutter 6y ago
http://musicfromouterspace.com http://musicfromouterspace.com is a great place to start. Going from simple dc arduino inputs to high precision analog is a bear, but super rewarding. Get ready to get your soldering skills right and start caring about resistor tolerances!
- tazard 6y ago
  WILL attract alien visitations - CAUTION ADVISED WILL DEFINITELY cut into TV viewing time - CAUTION ADVISED Stimulates plant growth and calms goldfish. Well thanks. There goes all my free time... But seriously, that website looks like an amazing resource
- franky47 6y ago
  I learned electronics from Ray's diagrams, he is truly missed. Another of my synth DIY mentors (with whom I worked on the Arturia MiniBrute) is Yves Usson: http://yusynth.net/index_en.php http://yusynth.net/index_en.php
petepete 6y ago
For a little extra inspiration have a look over Look Mum No Computer's projects. He's a little out there but has a deep knowledge and boundless enthusiasm. https://www.lookmumnocomputer.com/projects https://www.lookmumnocomputer.com/projects
- 6y ago

SeanLuke 6y ago

You'd think that making a fully digital square or sawtooth wave would be trivial compared to this, but in fact it's much, much more difficult because the digital wave must avoid aliasing, an issue the analog wave generator needn't concern itself with.

Applejinx 6y ago
Depends on how you approach 'trivial'. I've been hacking on Music Thing Modular Chord Organs for some time: they are a little Eurorack oscillator that can play chords, based on a Teensy. The Teensy audio library determines what waves you can get, and there's a 12 bit DAC built in. You can specify the sampling rate of the Teensy with a bit of fiddling, and the limits depend on what you're asking the audio library to do. The stock Chord Organ's set up to run at 44.1k, using a couple of submixes in the library to do things like set waveform levels independently. You can also set an oscillator to drive the output pin directly, with just one waveform. I've got a couple of 'em running at 2,822,400hz instead of 44,100hz. That's 2,822k for one oscillator (I can get four running at 768k), by telling the Teensy its sample rate is something hilariously high, just to run some square and 12-bit triangle and sawtooth waves. I avoid aliasing pretty well :) and it's definitely a fully digital DAC output. It's just good at being free from aliasing because I'm not concerned about what the sampling rate 'means' in terms of 'usable notes'. The only thing I care about is getting my waves nicer. The Teensy also has a rectangular wave, which is PWM adjustable. That, at 2,822k or even 768k, is quite nice even when it's a really thin pulse… And of course you could use the square to drive an integrator :)
- TheOtherHobbes 6y ago
  None of this was possible in the early 80s when the Junos were designed. The Cortex M4 in the Teensy runs at 200MHz. In the early 80s consumer-grade DSP didn't exist at all. There were some exotic studio processors with slow microprocessors supported by custom hardware multipliers, but 8MHz 16-bit microprocessors were considered fast, expensive, and exotic. Roland had a stellar run with their hardware designs. The Junos may be one of the best synthesizers ever made hitting the bullseye for price, character, simple but flexible programmability, and a legendary sweet but powerful sound. There's a finesse to this kind of audio design that IMO makes a lot of Eurorack seem clumsy and uninspired in comparison.

pen2l 6y ago

Just want to say that I was caught off-guard by the quality of the article, the text, the media, all of it. Bravo to the author.

barry27 6y ago

This is a great article.

bumbada 6y ago

I love the article. I did electronic music myself in the past, and this is very very good and detailed explanation. It motivates me to try it back. I have to find a little time to do something interesting now that I have the resources that I had not in the past(if only I had the time I had then).

nyanpasu64 6y ago

> The output voltage across the range can vary as much as 1 Volt, but that's fine- your ear won't really be able to tell the difference. If I understand correctly, the output from the sawtooth has a voltage offset? Can that lead to DC passing through speakers? And would the pulse-width comparator input need an equivalent voltage offset?

theacodes 6y ago
Yes, all of the waveforms out of the waveshaper have a DC offset. The synthesizer removes that when mixing them and sending them through the filter.
- nyanpasu64 6y ago
  Did you mean that the amplitude of the sawtooth can change by up to 1 volt (due to imperfections in the differentiator and amplitude compensator)? And if the PWM is based on comparing the sawtooth with a fixed voltage, and the sawtooth amplitude changes with pitch, does the PWM width change with pitch?
  - theacodes 6y ago
    You're correct. The pulse-width of the saw wave is very dependent on the amplitude of the saw, so when there's a 1 volt deficit in the saw wave's amplitude you lose about 8% of the pulse width. It's really not that noticeable in practice, though, and if anything it adds to the sonic character of the juno.

filoeleven 6y ago

If you like the sound of the Juno and don’t want to pay vintage synth prices for one, I highly recommend the Behringer DeepMind. It is clearly modeled after the Juno, and adds a lot of nice features (2 DCOs per voice, 2 more-capable LFOs, an arpeggiator, full FX suite...) and you can get the 12-voice keyboard model for about half of what you’d pay for a Juno 106. It’s got a big screen in the middle, but the front panel is designed so that you almost never have to use it, even when building patches. They have a great shortcut system for assigning modulation that’s easy to pick up and very fast to use. It’s just a great synth all around.