Nyquist Freq?

[Spyro]

Can anyone explain to me what is the so called "Nyquist Frequency"?

TIA

[stefancrs]

It's the highest signal frequency one can play back using a specific sampling frequency. This is always half of the sampling frequency.

So if having 44100hz sampling frequency the highest signal frequency that can be sampled / reconstructed is 22050hz.

Just use google.

[SKoT_FX]

The simplest signal you can represent in a discrete system is a sine wave, and that requires at least one "up" and one "down" value per cycle - hence why the Nyquist frequency is 1/2 the sampling frequency.

[Stupid American Pig]

above nyquist, you experience a phenominon called "aliasing". "Aliasing" is a subject of great debate- and while usually this should be relegated to the developers to hash out, you usually end up with end users trying to say how a certain synth/sampler is an Arsebiscuit(thanks for the word quincy) because it "aliases".

My general sentiment is that these threads usually pan out like this:

post 1"This synth sucks coz it aliases- what kind of synth engine is it? It doesnt sound like a virus or 303"
Post 2"this synth roxors, you are the one that sucks for not liking this synth "
Post 3"everybody sucks, and I cant hear the aliasing"
Post 4"Its there plain as day when you hit note 127 on your midi keyboard and boost the treble 12 db- you suck for not being able to hear it, you must not be a pro- my ears are better than everyone elses, plus I think that Cubase sounds better than FL studio, I can prove it coz my ears hear it"

and so on...

sorry for the sarchasm, but look around and you will see Im not *that* far off base

[mauseoleum]

somebody mis-spelled "no quest" and so the *nyquist theorem* was born.

[Spyro]

Thanks guys

So, when I get a sample, play very high notes and it sounds distorted, weird harmonics...thats because the sample goes above the nyquist freq right?

[no_signal]

Actually the Nyquist theorem says that you need at least 2 samples to store a sine wave on a digital medium, and then recontruct it with lowpass filtering in analog domain.
That is why the Nyquist frequency is half of the sampleRate.
The highest harmonic of a signal must be stored on at least 2 samples.

[no_signal]

Thanks guys

So, when I get a sample, play very high notes and it sounds distorted, weird harmonics...thats because the sample goes above the nyquist freq right?

Yes that is called aliasing (already mentioned) and it's a harmonic distortion. The spectrum of the signal is mirrored back at NyquistFreq, than it also mirrores at 0Hz, and you will end up with a lot of inharmonic content.
You can verify a harmonic as beeing alias or not by divide Fnyquist / Fharmonic, if you get an integer number, it is possible that you have aliasing.

[uncadave]

S_A_P-

[VicDiesel]

So, when I get a sample, play very high notes and it sounds distorted, weird harmonics...thats because the sample goes above the nyquist freq right?

You got it. If the Nyquist frequency if f and you try to play f+x, then it comes out as f-x, which is almost always inharmonious.

I think I posted the mathematical derivation of this in the aliasing thread.

V.

[mauseoleum]

sortof similar to AM radio.

[Voidoid Surrealist]

Ok, that explains the Nyquist frequency, but can anyone here help me understand the Nyquil frequency? Or why the holy f**k would you make the standard flavor of your product black licorice? The mind boggles...

[Borogove]

Yes that is called aliasing (already mentioned) and it's a harmonic distortion.

Actually, as you yourself describe further on in that post, it's an inharmonic distortion. Waveshaping, soft clipping, and hard clipping are examples of harmonic distortion.