Free Synth Promises To Emulate A Sequential Circuits Pro-One – But Can Your Computer Handle It?


Urs Heckmann of U-He has released RePro-1 – a free monophonic software synthesizer, for OS X & Windows, that he’s releasing as ‘research ware’.

He’s releasing it as a free ‘alpha’ release to gather feedback on the quality of several options for the synth’s filter models.

Heckmann says “It’s a first step in our recreation of the classic Sequential Circuits Pro-One monophonic synthesizer.”

“It is an excessively CPU hungry anti-optimized monophonic synthesizer,” he adds. “We have implemented the same pretty extreme model of the CEM3320 Curtis filter chip in our vintage Pro-One using 5 different numerical methods, each costing a very different amount of CPU. We wish for you to spot the “most analogue” sounding method. By that we wish to see if it is worth spending a lot of CPU, or if we could get away with something cheaper.

RePro-1 is available as a free download.

If you’ve tried RePro-1, leave a comment and let us know how your computer’s CPU faired.

23 thoughts on “Free Synth Promises To Emulate A Sequential Circuits Pro-One – But Can Your Computer Handle It?

  1. cant even get it to work… OSX 10.9.5, DP 9.02, Logic 9.18, Live 9.6….
    requires newer OSX? no documentation for anything besides the software license….

  2. 8 gb RAM
    AMD Quad Core
    2 TB RAM
    Windows 7
    FL Studio 11

    CPU issues 🙁 as always

    A hungry synth this one is but nice looking design and sounds nice

  3. The first issue is pure emulation; if it is authenticity that is sought then you use the most CPU draining method and wait for the tech to catch up, and run a single instance on a powerful machine till then. This will always have a level of balancing and optimizing, but knock yourself out with a mono emulation, and they do.

    Then you have a professional developer issue, if they can’t tell which is the best balance of power and sound then how can they expect the general public to make that call? You won’t get a real response, close to being random. Why?

    That Stradivarius blind test situation. Remember that one? They got together 10 professional soloists and 12 instruments, did the blind test to pick best sounding replacement instrument, and the new violin scores high and Strad scores low. So this has two aspects to it. A professional soloist is going to want to show people they know their shit, so even if they don’t prefer the sound of the Strad they are going to make that call upon hearing that sound, but they didn’t do that – they kinda showed themselves up in that regard. It is like someone from around here doing a blind test with some Yamaha CS emulation, if you hear the sound of a CS-80 then you are going to want to call that out before some cheap emulation, even if it sounds better, otherwise our lives are worthless here!!!

    If they are genuinely picking the new violin sound, as the best sounding instrument, then it shows you that a Strad has unwarranted status. It is all personal and deeply subjective. So in terms of emulation, you wouldn’t sample a Strad for the best sounding violin sample. That blind test raises a lot of calls regarding professional ears, sounds, and standards within that. Very much like the debate about grooves in plastic being the best form of media storage for audio that has ever been invented, that is how silly things can get; people are, generally speaking, f*cking useless.

    So people may not be voting on the best analogue sounding filter, or the best Pro One sounding filter. They may vote on the best sounding filter, and that may, or may not, be something that even sounds like analogue emulation.

    Maybe this blind test isn’t testing what people feel sounds the best, but it is testing our ears, and the worth of this resourceful approach in relation to that. They already know which is the best emulation, which is the best balance, and what they shouldn’t be doing, and what is the right way to go, that stands to reason. But I think within that they are starting to realize that people don’t have a clue. So if they can conclude that they can make the emulations less resourceful and have a much wider market. Otherwise it makes no logical sense to do this. The resourcefulness on U-he plugs is a bit of an in joke, in a good way – as we would all love a computer that could run those synths flawlessly.

  4. McBook Pro 13” 4Gb ram, 128Gb SSD, Intel Iris, Ableton Live Suite 9.5 , working at 48kHZ 256sample. It was just on 40% of usage… I though way more…. Anyway sound pretty good, pretty analog 😉

  5. Good Sound!
    Runs like a charm:
    16GB Ram
    in Ableton Live 9.6
    but leaches on the rescources 40% CPU with one instance.

  6. ON a >>
    macbook 2010
    2.4 GHz Intel Core 2 Duo
    8 GB 1067 MHz DDR3
    Ableton 9.5
    and runs ok…. if you don’t up the Rez up too much or set osc B to sub mode.

    I’ve managed to patch it up to use 96% CPU according to the monitor in Ableton (yes with just it running).
    And, Ableton does show a diff’ in CPU usage between the filter numbers.
    So much for a blind test. 😉

    ps. does sound good.

  7. Macbook Pro 2011 2.3Ghz quad , 16 gb , 250 ssd …. 1 instance of the synth without any tweeking playing one note takes 40-45 % cpu (in the ableton meter)….. Now my computer is not the fastest in the world but it is a neat little beast. This is why i don`t think it`s my computers fault but that of the Emulaton itself. i can`t imagine that i will be able to use it in an average project that needs 30-40 % cpu usage (with 4-8 analog synths in it) already without getting problems. I find this not to be the best programming i ever experienced. I mean there are plenty of classic analog synth emulations that don`t go even near this Cpu usage and i can`t say that they sound worse. I guess coding efficiency varies. This continuing “well we have the processing power nowadays, let`s reach the limits” but in the end creating always the same analog gear emulations i really don`t understand. Why does a good sounding analog synth Vst (example like the ones from Arturia to name one) works fine and needs 20% Cpu and a year later someone offers you basically the same sonic result but with 40% Cpu remains a mystery to me. Imagine what interesting results we would have if people move on from recycling in a high tech matter using canons to hunt ants. Cause at the end of the day it is like wearing fancy shoes but walking in circles. I appreciate the free version very much though

  8. Win 10 Pro x64, 3.1 Quad Core Intel i5, 8GB RAM, Focusrite Liquid Saffire 56, SSD for the OS, 7200RPM mechanicals for sample storage and recording.

    Seems to bump CPU usage up by 8% in Ableton 9.5 Suite, about 5% in Reaper 5.18.

    MacBookPro (mid-2012) seems to be about the same.

  9. Q6600, 4 gigs RAM, Windows 7 64-bit, Sonar 8.5.
    One instance uses 61% of CPU during playback.

    I found a sound I liked and tried to save it as a preset. When I brought up the preset-saving screen while I was playing back a short sequence, the synth randomly & arbitrarily reset itself and made a different sound. I could not save my preset because it was gone. This happened repeatedly.

    While I appreciate the kind free offer of this experimental synth, it is far too similar in intent to many free low-CPU monophonic synth emulations that have been available for years.

  10. This is meant to be a test, not a final version.

    What it doesn’t explain well in the summary above is that it always runs all 5 filter models simultaneously and you’re just choosing one of them to liste to. This was so people couldn’t tell during the test which of the models is the cheapest or most expensive to run, to see if it’s really worth using the most CPU-intensive version.

    So the final version will be a lot more efficient than this, and will have other known issues and limitations worked out.

  11. Yeah, you guys the point of this exercise was not to test the CPU load on your system but to choose which of the 5 filter types you like most.

    1. Yes, in fact one reason why the CPU load is so bad is that all five filters are running at once, though only one is actively outputting volume. That’s so there’s no noticeable lag or anything when you fire on a different filter type.

      That said, mine ran fine, never lagged, but crashed twice.

      1. Ian, yes that was Synthhead’s request, but I think he misunderstood the intention of this public alpha if you read the quote just above and Urs’ comments on the KVR page.

  12. Sounds really great!!!! Lovely. Thank you!!!!!

    iMac 21,5″ 2,7Ghz 8Gb. Runs well, but if you move any menu or window the sound stops.

  13. Sounds great here!
    Ableton 9.6 running on a Late 2013 MacBook Pro Retina, with i7 and 8Go RAM and OSX 10.11.3.
    CPU usage in Ableton is around 50% when using one instance of the plugin, no crash so far

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