Aliasing in synths. How to prevent it?

[BlitBit]

Is there any free VA synth which aliases (badly) so one can audition that phenomenon? I never really noticed aliasing anywhere, could be just the sounds i make, but i guess i never went that high to really be able to notice it.

Some examples for aliasing in oscillators can be found here:

• http://www.earlevel.com/main/2012/05/04 ... %94part-1/ (the saw tooth sweep at the bottom)
• https://ccrma.stanford.edu/~juhan/vas.html (naive implementation at the top)

The TripleOscillator plugin in LMMS also exhibits heavy aliasing if you play a saw in the higher ranges because it uses a naive implementation.

[Pyrotek45]

Is there any free VA synth which aliases (badly) so one can audition that phenomenon? I never really noticed aliasing anywhere, could be just the sounds i make, but i guess i never went that high to really be able to notice it.

Download a demo of sonic academy ana and use the init function. Then play a very high note(although in this synth, its very apparent even without going very high)

[chk071]

I just tried with Dune CM, but no anomalies there, sounds very clean also in higher octaves. I'll give ANA a shot then.

[fluffy_little_something]

Does any modern synth alias at 96kHz? I don't think I noticed any aliasing since I switched to 96kHz, not even with my old SE stuff.

What I do notice sometimes is an ugly grinding sound, but on middle octaves, and only when playing chords. I remember it from Retrologue for instance.

[EnGee]

Good questions. I hope I can learn their answers soon

[murnau]

What I do notice sometimes is an ugly grinding sound, but on middle octaves, and only when playing chords. I remember it from Retrologue for instance.

Have that too, it's my old cat!

[Urs]

Thank you for the answers

Do the answers apply on analog synths or just on digital ones (include VAs and soft synths)?

Analogue synths can not alias. Only digital synths (including digital emulations of analogue synths) can.

Glad you responded. I have a question. I really don't understand all this technical stuff. I try to stay away from it and just make music, but something has been bugging me and maybe you can help explain what's happening.

I recently purchased your Diva synth. Love it. Can't use it in Devine mode but at draft it sounds great.

However, one patch I made, when I play in the upper frequencies, I hear like a hissing sound in the background. Now from what I'm reading in this thread, this isn't aliasing. So exactly what is that? Is it something to do with how I have my filters setup? It's the only thing I can think of that would cause this to happen. There is no noise oscillator in the patch so that's not causing it.

Wondering if you or somebody else can offer some insight into this.

I'd need to check that preset out…

Of course Diva can alias, otherwise we wouldn't have had to add too many different quality modes (quality modes in synths are almost always related to aliasing, either on audio level or on modulation level). In Diva, Draft and Fast are commonly oversampled just 2x per module, so there's a good chance for some audible artifacts. OTOH Diva isn't necessarily an aggressive synth, so aliasing isn't the most important thing to worry about.

[fluffy_little_something]

I seems to have a lot to do with the programmer^s skills, on TAL's site it says about the U-NO-LX for instance:

- Improved alias free oscillators for an authentic sound also @ 44'100Hz sampling rate.

To me that sounds as if aliasing could simply be avoided if all developers knew how to do it.

Interestingly, he did not say anything about bit, as if 16 vs 24 vs 32 bit did not matter. Does it matter?

[trimph1]

I am not so sure it does myself.

I'm looking for info though.

[bbaggins]

Word length has nothing to do with aliasing. That is entirely down to sample rate.

[aciddose]

When we use the term "alias free" (I've done so myself in the past, unfortunately) it means only "free from aliasing above a threshold determined by the author under specific test conditions."

"Alias-free" just has a nicer ring to it. Technically correct would be "anti-aliased oscillators".

My criteria are: 20khz band at 48khz sample rate with a threshold of -80db, 1khz static (zero modulation) ramp, pure oscillator output.

At first I forgot to include test frequency and the pure oscillator criteria which are important.

[arkmabat]

I'm trying to understand what this is. Does aliasing happen at really low notes too?

[aciddose]

Yes, aliasing happens at all frequencies, all waveforms, always.

All non-continuous (continuous, aka analog) signals have infinite harmonic content.

You can reduce the amplitude of those harmonics but never eliminate them.

Anti-aliasing is any technique by which we aim to reduce harmonic content that would end up outside the band.

A band-limited signal is continuous. Any sampling of such a signal is no longer band-limited.

• Analog = Continuous
• Digital = Discrete-time

These are the proper terms.

[aciddose]

In fact don't assume band-limited continuous signals are common. They actually don't exist to my knowledge, they're impossible.

They're merely an abstract mathematical ideal, not something that is actually possible.

Although if you define both amplitude and frequency limits (0 to 20khz, -80db) you can define a signal as band-limited based upon those specific criteria.

[EnGee]

Thank you for the answers

Do the answers apply on analog synths or just on digital ones (include VAs and soft synths)?

Analogue synths can not alias. Only digital synths (including digital emulations of analogue synths) can.

Well, with the exception of an analog sample&hold. Aliases are generated in this case.

According to Urs explanation, it makes sense to have an analog synth (or a soft synth with high sample rate (or high quality mode) + fast cpu).

But according to aciddose even the analog synths alias. Does it means the analog synth aliases but at very low db levels?

If analog synths alias, which one has a clear example to search for?


What I'm thinking that for a big budget, it makes sense to go for analog polyphonic synth, but for someone with a small budget maybe monophonic analog will be ok for basses and leads while using high quality soft synth for pads ..etc.

What about the effects plugins? do they introduce aliasing for almost clean signals?

Oh and I thought aliasing only occurs with high frequencies!

Man! This topic is tough!