Antiphasing?

[mas]

Can someone explain me what antiphasing is?

Cheers!!!!

[lepton]

I?m a sound technician and the term antiphasing does not -at all- ring a bell to me.
Maybe I?m just ignorant and someone on this forum will give us both an answer.. hope so.
Anyway, I did a search on "antiphasing" on google and I came across "this" in the European Optic Society?s website.

I actually have no idea what it talks about... but you can download the full document on pdf format there

"(Abstract) we analyse the problem of intracavity second harmonic generation to determine properties of the antiphased states that have been observed in this system. We study the time-periodic solutions by means of a perturbation expansion in powers of a small parameter which is the ratio of the cavity lifetime to the population inversion relaxation
time. We prove that each mode intensity is characterized by two
oscillation frequencies though the total intensity oscillates with only one of these frequencies. In first approximation, we find that the bifurcation from the steady state to the periodic state remains vertical. We resolve this singularity by a complementary numerical analysis. We show that there are at least four distinct types of antiphase dynamics, including partial clustering of the oscillating modes into subsets of antiphasing states. Finally, we analyse the scaling exponent of the oscillation amplitudes near the bifurcation point and determine that the generic 1/2 exponent is the rule for only two of four types of antiphasing. The exponents of the other two cases depend on the mode number and partition."

[jasedee]

Originally Posted by mas

Can someone explain me what antiphasing is?

You didnt mean "Anti-Aliasing" did you?

[hatembr]

Originally Posted by jasedee

You didnt mean "Anti-Aliasing" did you?

to be honest, this has been discussed here many times but i still don't know what it is....... can anyone explain it plz ?

[jasedee]

When sampling at 44.1k, there are "Anti-aliasing" roll-off filters at around 21k that stop signals above the nyquist frequency (22.05k) from entering the A/D. If these signals were allowed to enter above the nyquist, they would produce artifacts somewhere in the lower range of the frequency spectrum (ie within humans range)

This is what I know "Anti-Aliasing" to be....maybe not the most detailed explanation, but the general idea I think

[hatembr]

and is this an audible effect ?
btw, what is nyquist ???

[Timo]

Originally Posted by hatembr

and is this an audible effect ?
btw, what is nyquist ???

Nyquist is the minimum digital recording frequency that is needed to capture a signal (to a minimal degree).

If you imagine a sine wave at 20KHz. - In order to capture that signal correctly digitally, you will need a mimimum recording frequency of 40KHz to capture it so you can be sure of including both the positive and negative rise and fall of a single cycle of the sine wave - otherwise the sine wave will be distorted and create phasing effects and other aliasing artefacts as the digital binary representation of a sine wave at a greater frequency would be impossible to reconstruct.

But to be honest when you get towards the top end of the Nyquist frequency aliasing still creates artefacts anyway, as pure sine waves are turned into triangle waves or much worse. The digital representation of a sine wave at its Nyquist frequency is not a faithful sine wave, but much more a distorted one, like a simple "on/off" waveform as opposed to smooth curves (although post-filtering helps at the Digital-to-Analogue stage).

The human hearing goes up to 20KHz+ . Therefore "CD quality" was designed to capture up to at least that frequency, so to do that they needed to record the signals at at least twice that frequency in order to capture and play back a 20KHz signal correctly. They eventually used 44.1KHz, which can play back frequencies up to 22KHz. But 44.1KHz is still effectively the minimum they can get away with. Higher representations are better, as they make the frequencies at 20KHz even more faithful (instead of being turned into triangle/saw/pulse waves), regardless of the fact we can't hear further than 22KHz+.

[Gopal]

Originally Posted by Timo

But to be honest when you get towards the top end of the Nyquist frequency aliasing still creates artefacts anyway, as pure sine waves are turned into triangle waves or much worse. The digital representation of a sine wave at its Nyquist frequency is not a faithful sine wave, but much more a distorted one, like a simple "on/off" waveform as opposed to smooth curves (although post-filtering helps at the Digital-to-Analogue stage).

Ah, the limitations of the stupid PCM recording format. Bring on the DSD recording algorithms!!!

[mas]

sorry guys,

I got it definitly wrong. I meant "anti-aliasing". Cheers for the explanation.

I'm still hanging around in Ecuador and just thougth I wanna have a look on that forum again. But I feel that I'm losing my English because of Spanish.

[jasedee]

Originally Posted by mas

I feel that I'm losing my English because of Spanish.

Bring on the Spanglish!