Noob question: What does aliasing sound like?

[grumphh]

Ok - i do know that aliasing is some frequencies being introduced into digital audio because of the math involved in said audio.

 

But what i honestly don't know is how aliasing sounds (or maybe rather what i should listen for) - even though i do have 3 unashamedly digital synths

 

(I guess it is because i mainly do weird sounds on these synths so that any weird frequencies get masked by the general weirdness i program in the first place)

 

So does anyone of you have an audio example of a single sound that does alias?

[urbanscallywag]

If you had a really simple sound, like a single sine oscillator, aliasing would occur if you pushed the oscillator's frequency over 1/2 the sample rate. As you raise the frequency of that sine past the 1/2 sample rate, you've aliased, and as you continue to raise the frequency of the sine it will actually go "down" in frequency.

 

So if I am sampling at 48 ksps (kHz) I can make a sine at 23 kHz (ignoring filters), but if I raise it to 25 kHz it sounds like 23 kHz because it has aliased and now "is" 23 kHz. Similarly 26 kHz will be 22 kHz...etc.

 

Aliased Frequency = Sample Rate - Sine Frequency

*Sine Frequency must be large than (Sample Rate)/2

 

In this example a pure sine is used, and aliasing doesn't sound too bad since there aren't any harmonics. As a signal with harmonics is aliased, the harmonic ratio is not preserved and the aliased overtones become inharmonic and probably don't sound too pleasing.

 

I can try and make some samples today.

[mcpepe]

[Delicious Lamprey Problem]

This is from Wikipedia:

 

Temporal aliasing is a major concern in the sampling of video and audio signals. Music, for instance, may contain high-frequency components that are inaudible to us. If we sample it with a frequency that is too low and reconstruct the music with a digital to analog converter, we may hear the low-frequency aliases of the undersampled high frequencies. Therefore, it is common practice to remove the high frequencies with a filter before the sampling is done.

[The Real MC]

 

So does anyone of you have an audio example of a single sound that does alias?

 

 

Anytime President Bush opens his mouth, that's aliasing.

[ElectricPuppy]

When I have a serious burrito and have to play some unsolicited butt tunes later? That's aliasing.

 

Particularly the freepers. Those can get some nasty low-end alisasing. Never trust a fart.

[DXelectro]

I've got a clip but it seems my old free upload server causes my internet to lock and only reset of the router brings it back. When I find another upload site I'l post my clip.

[Acid Hazard]

It actually kind of reminds me of a bit of ring mod when you play way in the upper keys. You can hear these strange artifacts in the the audio that def aren't supposed to be there.

[P321]

Might be a noob question, but I bet you'd be surprised at how many around here don't know the answer ..Anyway, here's a quick example of some

 

V-Station Aliasing.

 

An audio clip speaks a thousand words

[Yoozer]

Anytime President Bush opens his mouth, that's aliasing.

You mean polarizing

[ClavAnother]

 

Never trust a fart.

 

 

ever.

[grumphh]

Might be a noob question, but I bet you'd be surprised at how many around here don't know the answer ..Anyway, here's a quick example of some V-Station Aliasing . An audio clip speaks a thousand words

Thank you very much - more than a thousand words really - i get it now

 

And thx to all you others, my point was that i have read (and partly understood) the theory behind aliasing but i didn't have a sonic reference.

 

...and no wonder i have never been able to isolate aliasing before, my sounds sound like that all the way down to the lowest octaves

[DXelectro]

Urbanscallywag has got it right.

 

 

As a signal with harmonics is aliased, the harmonic ratio is not preserved and the aliased overtones become inharmonic and probably don't sound too pleasing.

 

 

I would add that sometimes you can use aliasing to your advantage. The reflected frequencies sometimes can sound interesting and pleasing. I played an upward chromatic scale on the DX7 with a simple sound that aliases and it sounds sweet once it begins to alias.

 

Too bad there is something wrong with my broadband. I can't upload anything anywhere using my Vista / XP / Explorer / Firefox (all combinations) machines.

[urbanscallywag]

It actually kind of reminds me of a bit of ring mod when you play way in the upper keys.

 

I was almost going to put that in my original post but I didn't. The reason is as mentioned in the original post that harmonics become inharmonic as they fold over the 1/2 sample rate. Ring modulation and frequency shifters cause inharmonic tones also.

[urbanscallywag]

Might be a noob question, but I bet you'd be surprised at how many around here don't know the answer ..Anyway, here's a quick example of some V-Station Aliasing . An audio clip speaks a thousand words

 

Wow that's bad news.

[P321]

Wow that's bad news.

I should just say that the aliasing in that clip is primarily caused by the V-Stations FX if memory serves, not its actual oscillator code.. So its nowhere near as bad as the clip suggests

[listenman]

I had the same question recently and stumbled upon this. I could not access the previous link posted by P321. Here's a youtube video I found where you can hear aliasing.

 

 

 

 

[moogerfooger]

watch this

 

[video=youtube;Ic4bVbXfdW4]

 

 

remember that if you sample at at least twice the frequency range -- no aliasing happens, 44.1K is twice 22.k which is way above most peoples hearing

[Cydonia]

Oh, Hai !

 

:wave::wave:

 

It looks like this :

 

 

And it sounds like this :

 

 

Oh and...

 

I haz a Kronos.

 

And where is everyone ?

 

[1001gear]

Play only voice patches till you get it.

[Cydonia]

[1001gear]

Dead is the latest thing.