Aliasing and hardware synths

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madtheory
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Re: Aliasing and hardware synths

Post by madtheory » Wed Oct 18, 2017 12:35 pm

No one said the oscillators were analog. There are lots of ways to make a synth "digitally" that are not VA.

Is there documentation about the alias- free claims? Is it a 12MHz SR?

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Re: Aliasing and hardware synths

Post by meatballfulton » Wed Oct 18, 2017 1:45 pm

Novation claims oversampling at 12Mhz in their product blurbs. That's properly the D/A spec, of course.
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Re: Aliasing and hardware synths

Post by Ashe37 » Wed Oct 18, 2017 4:53 pm

would explain why its proven so difficult.

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Re: Aliasing and hardware synths

Post by madtheory » Wed Oct 18, 2017 5:00 pm

Ya 12MHz is not unusual for a DAC. 12MHz in the ENTIRE synth engine is unlikely, but there are probably parts of the code that are over-sampled, would explain the FPGA, and the price. Or maybe they did the Synclav resampling trick accreil describes? Let's go look for any patents they have- Novation, Focusrite, Chris Huggett... anyone remember the company owner's name? He's in the "History of Novation" doc. Which is great, BTW.

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Re: Aliasing and hardware synths

Post by madtheory » Wed Oct 18, 2017 7:11 pm

The internet is back after Ophelia! :)

It's all here (the simple version, at least):
https://us.novationmusic.com/peak-explained

There's a DAC per voice. These are not normal oscillators nor are the wavetables like normal "samples". They've done something ingenius here.

Bandwidth= 12MHz.

There's NO WAY to make this thing alias audibly.

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Re: Aliasing and hardware synths

Post by Ashe37 » Wed Oct 18, 2017 8:45 pm

But trying has been interesting

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Re: Aliasing and hardware synths

Post by madtheory » Thu Oct 19, 2017 12:31 pm

https://www.soundonsound.com/reviews/novation-peak

"All we musician types really need to know is that the high clock speed is responsible for the pure and accurate waveforms that don’t suffer from the usual levels of aliasing — although some artifacts are discernible at the extremes of transposition."

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Re: Aliasing and hardware synths

Post by desmond » Thu Oct 19, 2017 1:18 pm

madtheory wrote:The internet is back after Ophelia! :)
I hope it didn't affect you too dramatically... :o

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Re: Aliasing and hardware synths

Post by briandc » Tue Oct 24, 2017 4:29 pm

Thanks for all the great info everyone. (Sounds like this thread got Ashe37 into some good tweaking, so that's always good! :D )

So if I understand right, aliasing can be avoided/eliminated by:

- raising the D/A sample rate, or
- using faster digital waveforms, or
- not playing above a certain frequency.

Yes?

brian

PS. Watching Novation Peak video. --Isn't 8-voice polyphony a bit "low?" I thought by now we'd have (digital) synths with much more polyphony and without going back to the "old limits" of previous technology..
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Re: Aliasing and hardware synths

Post by Ashe37 » Tue Oct 24, 2017 4:44 pm

The Peak has analog multimode filters, it isn't just a 'digital' synth.

And yes, as stated above, i was able to get some aliasing at the far extremes of transposition... like, the top five or six notes.

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Re: Aliasing and hardware synths

Post by madtheory » Wed Oct 25, 2017 10:10 am

Yes it is an 8 channel synth, with a DAC for each channel. It's effectively a digital/ analogue hybrid. Hence the price!
briandc wrote:So if I understand right, aliasing can be avoided/eliminated by:

- raising the D/A sample rate, or
- using faster digital waveforms, or
- not playing above a certain frequency.
Yes, those are all ways although I'm not sure what you mean by "faster" digital waveforms. I think what is meant here is oversampling? But this can be done in a filter, and a VCA, and an envelope too, as well as just the oscillator. It just requires processing power. It's the done thing in (modern) compressor and eq plugins, for example. Internally use some high rate, so that frequencies above Nyquist are correct, then apply the LPF to remove them before output to DAW at the standard rate (44.1kHz or 48kHz, for example). Some plugins let you turn oversampling off, to save processor power. Hopefully the aliasing is not audible. Often it isn't, because it is just below Nyquist, and not as loud as the music. Bit risky though.

There are also some clever maths tricks to make that less processor intensive. Check out acreil's analysis of the Yamah DX-7. Now that was some seriously clever minimising, in order to maximise system resources.

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Re: Aliasing and hardware synths

Post by Bitexion » Wed Oct 25, 2017 11:50 am

On my old D-50, if I do a single sawtooth, set the pitch stick to +24 notes, hold the topmost key, and start messing with the pitch stick, it sounds like oldschool ringmod. Kinda cool effect actually.

I also remember beta testing a memorymoog VST some years ago, where the sound would go into a screechy, ringmod-like mess the moment you upped the resonance on some of the filters. Why does this happen anyway?

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Re: Aliasing and hardware synths

Post by madtheory » Wed Oct 25, 2017 12:13 pm

Bitexion wrote:Why does this happen anyway?
Because there is no over-sampling and anti-aliasing filter in the code. A.K.A. bad maths :)

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Re: Aliasing and hardware synths

Post by briandc » Wed Oct 25, 2017 2:56 pm

madtheory wrote: Yes, those are all ways although I'm not sure what you mean by "faster" digital waveforms. I think what is meant here is oversampling? But this can be done in a filter, and a VCA, and an envelope too, as well as just the oscillator. It just requires processing power. It's the done thing in (modern) compressor and eq plugins, for example. Internally use some high rate, so that frequencies above Nyquist are correct, then apply the LPF to remove them before output to DAW at the standard rate (44.1kHz or 48kHz, for example). Some plugins let you turn oversampling off, to save processor power. Hopefully the aliasing is not audible. Often it isn't, because it is just below Nyquist, and not as loud as the music. Bit risky though.

There are also some clever maths tricks to make that less processor intensive. Check out acreil's analysis of the Yamah DX-7. Now that was some seriously clever minimising, in order to maximise system resources.
I was referring to your earlier post where you quoted a part that said that "the high clock speed is responsible for the pure and accurate waveforms." Now I see I should have said "fast CPU speed" rather than "fast waveforms." :oops:

Which makes me wonder why so many of the modern softsynths have "luxurious" GUIs that many systems have to work hard to deal with. Better to make a simple GUI (or better yet, use a terminal!) and dedicate that CPU "energy" to good quality audio! Right?


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Re: Aliasing and hardware synths

Post by madtheory » Wed Oct 25, 2017 3:30 pm

Well, I think the UI is super important. A synth is no use if a person cannot use it, especially in a way that is fun and intuitive. It should not be hard to make cool sounds. Nor should there be any snobbery about a synth, based on its UI. For example the MicroKorg- it is one of the better sounding VA engines, kind of a classic at this stage. But MS2000 prices :)

But then you get UIs that are more about the look, than the user interface. Like the older Arturia plugins. New version has it right though, at least on the ARP2600. That is very fun :)
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madtheory wrote:The internet is back after Ophelia! :)
I hope it didn't affect you too dramatically... :o
Ya, it did get dramatic:

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