Do hardware VA's alias as badly as software?

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Aroused by JarJar wrote:
hakey wrote:
Aroused by JarJar wrote:"naive" (aka theoretically perfect) saws and such.
theoretically perfect = harmonically perfect?
Don't know what you mean by "harmonically perfect". I just meant for example that a theoretically perfect saw would have zero rise time (instantaneous change from -1 to 1) and an absolutely straight direct ramp between 1 and -1. This doesn't happen in reality, as the finest analog doesn't operate at infinite speed and bandwidth. In digital this waveform is represented by a "naive" line from 1 to -1. This aliases like a hell.
Just trying to clear up some potential confusion there. To me a theoretically perfect saw would be one with infinite harmonics that followed the 1/n amplitude rule. Naive saws are indeed geometrically perfect, but not harmonically perfect.

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If I was spiteful, I'd have my lawyer send cease and desist letters to any company that claims to have "aliasing free oscillators" in their digital synths. Our lawyer could actually make a living from that.

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Aroused by JarJar wrote:I think it's rather a matter of you're being confused by your own intent to pick at whatever I say rather than actually try to understand it.
What you said was confusing. And any occurrence of the '48kHz is insufficient to capture the harmonics' canard will inevitably draw comments.
And you still seem to be suffering from the delusion that all VA variably generate waveforms.

Edit: fair enough, I did say "VA oscillators aren't sampled and repitched".I should have said that "good quality VA oscillators are generated" or similar. :oops:

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So the look-up table method, does this, as AJJ suggest, simply involve sampling a waveform at a single frequency and then repitching it, with the undesired effects (missing harmonics for low pitches aliasing for high) following on from that?

Are there any modern VA's that use such a crude method?

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Roland Gaia uses such method, its oscillators are sampled. O.o'

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Urs wrote:If I was spiteful, I'd have my lawyer send cease and desist letters to any company that claims to have "aliasing free oscillators" in their digital synths. Our lawyer could actually make a living from that.
Wait a second, but what about representation as sum of sines: k1*sin(x) + k2*sin(x*2)+ ... + kn*sin(x*n) - it's perfect aliasing free osc, ain't it?
Murderous duck!

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EvilDragon wrote:Roland Gaia uses such method, its oscillators are sampled. O.o'
A single sample repitched for the whole frequency range (as per AJJ's argument)?

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Not a single sample IIRC. I don't remember correctly, but it might be a set of single-cycles for each key. Or something like that.

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david.beholder wrote:
Urs wrote:If I was spiteful, I'd have my lawyer send cease and desist letters to any company that claims to have "aliasing free oscillators" in their digital synths. Our lawyer could actually make a living from that.
Wait a second, but what about representation as sum of sines: k1*sin(x) + k2*sin(x*2)+ ... + kn*sin(x*n) - it's perfect aliasing free osc, ain't it?
yes - and that's the way, i rendered the example file for the anti-aliased sawtooth. it's not very practical for a realtime-synth, though. in a realtime-synth, you will typically have some kind of trade-off between between computational cost and the level of aliasing.
My website: rs-met.com, My presences on: YouTube, GitHub, Facebook

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Robin from www.rs-met.com wrote: it's not very practical for a realtime-synth, though. in a realtime-synth, you will typically have some kind of trade-off between between computational cost and the level of aliasing.
DIVA doesn't know any cpu tradeoffs :) Altho i guess it's not using sum of octave sines :)

Frankly, I can't imagine how fast are modern FPUs - might be very realtimish for say 10-20 harmonics
Murderous duck!

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nm
Last edited by dreamkeeper on Tue Nov 20, 2012 1:59 pm, edited 1 time in total.
The hole is deeper than the hum of its farts

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Just to be clear, waveforms generated using a band-limiting method must necessarily exhibit some aliasing, therefore anyone claiming that their (advanced) band limited impulse train oscillator is completely alias free is telling porkies?

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hakey wrote:Just to be clear, waveforms generated using a band-limiting method must necessarily exhibit some aliasing, therefore anyone claiming that their (advanced) band limited impulse train oscillator is completely alias free is telling porkies?
hmm - well, not necessarily. it is theoretically possible to obtain perfect results. but it is not always practical. additive synthesis was already mentioned as a means to generate perfectly alias-free waveforms. discrete-summation-formulas may also give you perfect results. it's only that both of those have other drawbacks: the former is computationally expensive, especially in the low registers and the latter has some problems with transients and/or DC offsets. the more practical methods like (Min)BLEP and mip-mapped wavetables will not give perfect results, but arbitrarily good approximations and the goodness of the approximation will depend on the computational cost, you are willing to spend. i found my own sweet spot somewhere, where the aliasing was pushed somewhere below 100 dB (where i can't see it anymore on my spectral analyzer :hihi:). a simple one-line change in the code could push it even further down, but i found it not to be worth the increased CPU usage.

BTW.: what are porkies?
Last edited by Music Engineer on Tue Nov 20, 2012 2:16 pm, edited 1 time in total.
My website: rs-met.com, My presences on: YouTube, GitHub, Facebook

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david.beholder wrote:
Urs wrote:If I was spiteful, I'd have my lawyer send cease and desist letters to any company that claims to have "aliasing free oscillators" in their digital synths. Our lawyer could actually make a living from that.
Wait a second, but what about representation as sum of sines: k1*sin(x) + k2*sin(x*2)+ ... + kn*sin(x*n) - it's perfect aliasing free osc, ain't it?
For a static sawtooth waveform, yes.

But if you add vibrato or any more drastic kind of pitch modulation, then you would have to e.g. insert BLEPs or similar means on each change of derivate, e.g. per sample.

This isn't viable and it's also not necessary to reduce aliasing below perceptible levels, but to believe that any digital oscillator with a common feature set is "aliasing free" is naive.

Even worse, making oscillators "aliasing free" doesn't mean that filters etc. do not alias. This is usually met by oversampling. Which involves filtering that reduces aliasing, but can't eliminate it.

All digital synths I tested in the past year or two have relatively aliasing-free oscillators and quite audibly aliasing filters and/or waveshapers.

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Robin from www.rs-met.com wrote: BTW.: what are porkies?
rhyming slang: pork pies = lies :wink:

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