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 Forum index » Clavia Nord Modular » Nord Modular G2 Discussion
Whats the aliasing like on the g2
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Macrostructure



Joined: Sep 04, 2004
Posts: 27

G2 patch files: 3

PostPosted: Tue Sep 28, 2004 2:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Er...what is aliasing?

Anyone got a simple explanation?

t
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ian-s



Joined: Apr 01, 2004
Posts: 2575
Location: Auckland, New Zealand
Audio files: 42
G2 patch files: 608

PostPosted: Tue Sep 28, 2004 4:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Aliasing is an effect (normally unwanted) caused by interaction between the sampling frequency and frequencies present in what is being sampled, or generated. In theory, an audio signal should have zero level for any harmonics a little less than half the sample rate. If not, then fold over frequencies occur which don’t necessarily have any relationship harmonically to the original. A visual analogy is when you see an old movie where a vehicle or wagon drives off, as the rotation of the wheel approaches, then exceeds the camera frame rate, the perceived motion slows then reverses direction.
In relation to virtual analogue, real analogue vco’s with fast transients like saw and rectangle waves contain harmonics well above even 192K, generating ‘band limited’ versions of those waveforms is probably the most difficult part of VA. The aliasing frequencies cannot be effectively filtered from a trivially generated sawtooth. Rolling Eyes
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Rob



Joined: Mar 29, 2004
Posts: 580
Location: The Hague/Netherlands/EC
G2 patch files: 109

PostPosted: Tue Sep 28, 2004 4:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Tim wrote:
Er...what is aliasing?

Anyone got a simple explanation?

t


Explanation of anti-aliasing can by nature not be simple, but lets give it a go: Smile

When an analog signal is digitized there is a minimal difference with the original analog signal due to the quantization precision. When this difference is large, e.g. when only a low precision is used, it sounds like the famous 'lofi' effect. When a digitized signal is plotted on paper it will not look smooth but slightly stepped. These little steps can sound like a very high frequency buzz.
It is the same as the difference between the 'jagged' characters on a computer screen and the smooth characters in a printed book. Characters and diagonal lines on a computer screen can be made to look smoother by using extra dots in different shades of grey, which is also named anti-aliasing.

Basically anti-aliasing is creating an illusion which appears more smooth to the human mind than it actually is. In other words, how something can be made to 'appear' more accurate with the same amount of data, e.g. the same number of pixels on a screen.

The quantization precision depends on two things, first is how many times a second an analog signal is measured and second the actual precision of the measurement. The more measurements a second plus the finer each measurement will increase the precision and make the sound cleaner.

When an analog signal is calculated with a digital processor there is the same difference from the 'ideal' analog signal as when an analog signal is measured. The more precise the calculations are, plus the more precise the digital to analog converter used by the processor, the cleaner the sound. The calculation method named 'anti-aliasing' tries to calculate the analog waveforms as accurately as possible by 'correcting the bandwidth' during the calculation of the waveforms. This calculation method is not straightforward and can be implemented in different ways, and in a way defines the sound quality of the digital instrument, or better what it can and cannot sound like. The cleaner the basic sound the more you can actually do with distortions, EQ, etc. later.

How anti-aliasing works in practice is based on the fact that the number of measurements a second also limit the frequency bandwidth of the signal. There can be no frequencies that are higher as half the sample rate. And frequencies that approach half the sample rate will produce a lot of digital artifacts, as the closer a frequency is to half the sample rate the less precise the waveform becomes as the waveform will be represented by only a very few numbers. So, the purpose of anti-aliasing is to prevent those frequencies to be generated that will come close to half the sample rate and thus produce the 'lofi' buzz or even severely out of tune 'ghost frequencies'.

When talking about the G2, lets just say that it does quite well compared to other 'virtual analog' synths and plug-ins. The disadvantage of a very clean digital synth is that it can easily have a 'sterile' sound. The good thing about the G2 is that this sterile sound can be made a little bit warmer and 'dirty' by patching tricks within a patch. Not by making the sound more 'lofi', but instead by creating the non-linear distortions that typify pure analog equipment. So, the G2 sounds very clean by default, but can be made to sound quite grungy with the proper patch tricks. Imho a good example patch of as nicely grungy sound is the organ made by Åke Danielson in the factory preset patches.
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Rob



Joined: Mar 29, 2004
Posts: 580
Location: The Hague/Netherlands/EC
G2 patch files: 109

PostPosted: Tue Sep 28, 2004 4:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Tim wrote:
Er...what is aliasing?

Anyone got a simple explanation?

t


Now you got two explanations. Shows the deepness of the subject. Very Happy
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ian-s



Joined: Apr 01, 2004
Posts: 2575
Location: Auckland, New Zealand
Audio files: 42
G2 patch files: 608

PostPosted: Wed Oct 06, 2004 12:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

I don’t know exactly when, but Clavia have made some improvements to the G2 anti-aliasing. In relation to non audio modules being used at audio rate (logic modules, level compare etc). Originally, this caused quite bad aliasing even though the module turned red/orange. Things have improved so that, for example, using a level compare module to get a variable width pulse wave from a sawtooth, produces much less aliasing than before. See my posted SH1 for an example.

http://electro-music.com/forum/topic-2724.html

I often look for new ways to abuse modules to hear what comes out Rolling Eyes
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