the limit of anti-aliasing

CharlesFerraro · Post by **CharlesFerraro** » Wed Oct 19, 2011 3:37 am

I was doing some experiments with the RADIAS as a test generator and it seems the MMT engine is unable to produce a tone above G#9 or 13,289.6Hz.

If you go above this frequency the next note will start an octave lower.

I tried inserting the pitch shifter to go beyond this frequency and strange 'ring mod' type sounds ensue when I try to push the engine beyond this limit.

My guess is its some anti-aliasing governance. Even a resonant filter sweep cannot break this limit, if tried, the sound does produce aliasing.

Here's the sound of the octave reset, then the 'ring mod' pitch shift, and finally filter aliasing:
http://soundcloud.com/wolf-ray/mmt-anti-aliasing

CharlesFerraro · Post by **CharlesFerraro** » Wed Jan 04, 2012 3:48 pm

Turns out it does this octave reset on extreme low notes too. Hmm...

tpantano · Post by **tpantano** » Wed Jan 04, 2012 4:23 pm

It'd be great to know the limits for curiosities sake.

But you'll never need to reach certain octaves D: Once you go into certain high octaves for example, the harmonics of say, a saw, become non-audible, resulting in only the base frequencies which would generate with other functions like filters at a lower octave.

thehighesttree · Post by **thehighesttree** » Thu Jan 05, 2012 12:47 am

Thanks for looking into this! My setup's almost totally MMT-based so I'm trying to learn how to keep things sounding smooth through a mix.

Re-Member · Post by **Re-Member** » Thu Jan 05, 2012 3:16 am

Someone who worked for Korg actually made a comment about this on the Harmony Central forums:

"Hi all,

So great to see this thread. I just thought I'd point out a few things.

First, "Ultra Low-Aliasing Oscillators," one of the under-the-hood technologies in the RADIAS, might be responsible for the clear/bright/glassy descriptions that I'm reading here. It's also present in the Kronos, OASYS, R3, and microKORG XL, and it enables very high-pitched sounds without imperfections caused by aliasing. The end result of this is that the modeled waveforms stay pure throughout an extremely wide frequency spectrum, even during pitch bending and fast LFO motion.

I'd hope this won't distract you from the massive bass capability in the RADIAS, because it can certainly shake the floor... But it's worth mentioning that it shares some of this specific development that also went into our flagship workstations.

With regard to the electric piano sounds: McHale correctly pointed out that the RADIAS does more than analog modeling. It also has PCM sounds, as well as VPM (a new take on FM-style synthesis). There are examples of electric pianos that use all these different technologies, so it'd be interesting to hear which ones you like.

I'm glad to hear that so many of you are enjoying the RADIAS. As someone who has spent many a late night pushing it to its limits, I encourage you to keep exploring. There's an awful lot to discover.

Thanks,
-Rich

Richard Formidoni
Technology Product Manager
Korg USA, Inc."

Re-Member · Post by **Re-Member** » Thu Jan 05, 2012 3:22 am

My experience with newer Korg gear is that the default tone tends to be really loud in the mid section, but quieter in the lows and highs. I typically use an EQ or limiter effect to tone down some of the mid frequencies so the bass comes through better if I'm aiming to play a wider range of keys within my patches. Compressor is good too, but only if you're playing monophonic sounds.

CharlesFerraro · Post by **CharlesFerraro** » Thu Jan 05, 2012 3:53 am

To be honest, I think its kind of silly that they boast about this "low-aliasing" business. There are a few soft synths (Prologue, Carbon2) and even synths for the iPhone that have zero aliasing oscillators. Maybe people don't like that "cold digital clarity" and prefer a little grit in the signal. Coming from a sound design perspective though I'd rather have as sharp and clean an instrument as possible. Remember its much easier to dirty a signal than it is to clean it up.

X-Trade · Post by **X-Trade** » Thu Jan 05, 2012 7:32 pm

CharlesFerraro wrote:Coming from a sound design perspective though I'd rather have as sharp and clean an instrument as possible. Remember its much easier to dirty a signal than it is to clean it up.

This is what I usually think too.

Worth pointing out though that many traditional analog synthesizers are also actually quite clean. The 'aliasing' is a very digital kind of distortion that can have its own unique character but can also be highly undesirable for some types of sounds.

I often use a the decimator/bit crusher to get dirtier sounds.

tpantano · Post by **tpantano** » Fri Jan 06, 2012 1:17 am

CharlesFerraro wrote:Remember its much easier to dirty a signal than it is to clean it up.

Now that I've been working with synths for a while, I completely agree with this.

A bit of gain/limiter distortion or a plug-in like Massey Tape can make any synth, even the coldest of cold, warm... but going backwards, removing the mess from a mess, is really difficult.

CharlesFerraro · Post by **CharlesFerraro** » Fri Jan 06, 2012 4:17 am

X-Trade wrote: Worth pointing out though that many traditional analog synthesizers are also actually quite clean.

very very good point. I feel like Moog Voyagers are exceptionally clean, at least the few i've got to fiddle with. the dsi desktops are real sharp too. I got to try out a juno60 on the other hand and that thing was a total mess. Modern analog synths are exceptionally calibrated.

Re-Member · Post by **Re-Member** » Fri Jan 06, 2012 6:35 pm

Personally, I don't mind the clean sound of the Radias/R3 engine. All of the digital Roland gear I've owned throughout the years have had aliasing problems that result in either a distorted clipping effect (similar to an album being digitally mastered too high), or just this weird wheezing sound that drowns out the original tone to where the notes are indistinguishable. It's like the filters attempt to self-oscillate, but fail at it.

Sure, the way the Radias/R3 limits some of the frequencies initially to avoid these problems can make the sound too mid-rangy (if that’s even a word, heh), but as I said, the EQ section really helps a lot. Just dial in the lower and higher frequencies you want and boost them in. It’s very flexible. The fact that the EQ operates separately from the effects show that Korg took it into consideration that some might not like the initial tone.