First, I don't want to join each of the two sides, i'm swiss, i'm neutral
Nevertheless i'd like to see some positiv conclusions going on here, else it's useless at least for me...Ok, let's start. Just wanted to bring in a new point in this discussion. All posts are based on phase, phase shifting, phase polarity etc...
So what the hell are all these things exactly?! I think the problem is that we are talking about different things here. I'm not that good in all that phase stuff, it's way beyond my knowledge, so now it's time for the Pros to explain what we are talking about here!!
Ok, did some research and I found some nice explanations about phase in another forum, see here:
<i><b>What you do with phase on a computer</b>
Let's say you've got your sine wave file. Looks something like this:
<IMG SRC="http://forum.videohelp.com/images/guide ... nphase.gif">
This would be like how the waveform displays in an audio editor. It puts each sample on the graph, depending on sample time (x axis) and sample volume/intensity (y axis). Notably, the y axis can be positive or negative (meaning "compressing" or "decompressing" the air relative to normal atmostpheric pressure--but I said we weren't going to get into that).
Positive y = Positive analog voltage = Speaker Moving Outward = Compression,
Negative y = Negative analog voltage = Speaker Moving Inward/Backward = Decompression
Now let's look at a different sine wave file.
<IMG SRC="http://forum.videohelp.com/images/guide ... eshift.gif">
It looks just about the same. For most purposes, it is the same. One minor exception seems to be the initial delay. It's not really delay, it's "Phase Angle". Since the Sine function relates to the Phase Angle of a circle, where you start on the circle determines what the given intensity is at that point in time. This one is out-of-phase with the first one by a small amount.
Look what happens when you superimpose to two:
<IMG SRC="http://forum.videohelp.com/images/guide ... sesine.gif">
This more clearly shows the relationship between the 2.
However, when mixed (digitally, electronically, or aurally), they combine to show a new wave that is the vector addition of the 2 waves:
<IMG SRC="http://forum.videohelp.com/images/guide ... esine2.gif">
Because of the vector addition (which incorporates the phase angle) and because of the fact of having the possibility of Positive and Negative intensities, weird things can start to happen (called interference)...
If they are identical in phase (basically just 2 copies of the same file), they have constructive interference and add together to be twice as loud.:
<IMG SRC="http://forum.videohelp.com/images/guide ... sesine.gif">
If they are completely opposite in phase (i.e. "Reverse Polarity" or "Inverted"),
<IMG SRC="http://forum.videohelp.com/images/guide ... tphase.gif">
then together they have destructive interference and subtract, creating a total wave of ZERO or complete silence.:
<IMG SRC="http://forum.videohelp.com/images/guide ... sesine.gif">
<b>--- sidenote from katano: this is what martin tried to reach, isn't it?</b>
Of course, realworld signals have multiple frequencies and harmonics and vary their levels, so nothing is so cut & dried, it's much more complex than that.
Phase inversion/shifting allows you to do the complex mixing required so that you can add (matrix) files together at one stage, and (nearly completely) recover the original files at a later stage (decoding). Dolby Surround/PL/PLII is based on this priciple of 4:2:4 matrixing.
There are other psychoacoustic uses for phase adjustment as well. </i>
that's all folks...
greez
roman
<font size=-1>[ This Message was edited by: katano on 2006-09-25 05:39 ]</font>
