Phase expalined....

[RAMI]

People often say they don't really understand phase. I found this video. Maybe some of the more knowledgeable people here can confirm or dismiss weather this is a good explanation. It seemed to make sense to me.

https://www.youtube.com/watch?v=sba-sRo3UQI&NR=1

 

[The Green Hornet]

A nice "Expalination."

Green Hornet

 

[RAMI]

A nice "Expalination."

Green Hornet

Hehe...you caught that, didn't ya????

 

[danny.guitar]

Good video. I'm watching some of his others now, right now the recording acoustic.

Seems like some good stuff.

 

[XLR]

He did a good explanation.

 

[cusebassman]

hehe just watched the acoustic recording one myself - useful stuff - its nice to see he gets a much bassier, boomy sound from his guitar as well when using an LDC on acoustic

 

[InternetH3ro]

Excellent video, thanks! Lots of other decent seminars as well, very good find.

 

[Robert D]

I like the title; "Phase, what is it and how to avoid it". Yep, I like to have no phase in my recordings at all. In phase, out of phase....it's all bad. No phase is the only way to go.

 

[XLR]

I like the title; "Phase, what is it and how to avoid it". Yep, I like to have no phase in my recordings at all...

Heh, I didn't even notice the title but yeah that's funny.

 

[RAMI]

...but wouldn't 2 "no-phase" signals cancel each other out and give you more phase than you know what to do with???? I think the best thing would be to combine 2 "no-phase" signals...but make sure one of them is out of no-phase.

 

[Elton Bear]

I laughed too, does that make us geeks? It really does, doesn't it?

 

[Ethan Winer]

Maybe some of the more knowledgeable people here can confirm or dismiss weather this is a good explanation.

That's a pretty good video, but he makes the classic error of confusing phase with polarity. What that video addresses is polarity. This is not at all the same as phase.

--Ethan

 

[Robert D]

Silence has no phase, except for Hollywood's silent movie phase.

 

[Robert D]

That's a pretty good video, but he makes the classic error of confusing phase with polarity. What that video addresses is polarity. This is not at all the same as phase.

--Ethan

So if you take a signal, split it, and send the two identical and phase coherant signals through identical amps to identical speakers, and then reverse the polarity of one of the speakers, aren't the resulting waves 180% out of phase with each other, measured at the same distance from each of the cones? The cause of the inverse phase relationship is reversed polarity, but the waves aren't said to have reverse polarity. Yes, no?
This differs from, let's say running one side through an LC network that induces a phase lag of 180 deg. Now the waves are out of phase, with a 1/2 cycle phase delay, but both cases still create two acoustical waves that are described as being 180 deg out of phase with each other, I think.

 

[flatfinger]

While they do look the same on an oscilliscope , one is a result of polarity reversal while the other is a result of time lag. Of course, the results will also be dependant upon what frequency is being fed through the LC network. The resultant phase shift shifts as the frequency changes. Thats why if you hook up 2 mics , play a tone an walk around with the 2nd , the tone changes due to comb filtering as you change your distance from the 1st mic. (aside from th rooms tuning )

 

[SouthSIDE Glen]

Inverse polarity and 180° pahase rotation only necessarrily appear the same when talking a simple periodic waveform such as a sine or a square wave. Take a complex wave, though and that seemingly obvious relation disappears.

As flatfinger correctly stated another way, the amount of phase shift caused by a delay in time varies by frequency. For example, only those frequencies that are equal to or even diivisions of x cycles per second will appear to be be 180° out of phase when shifted by x cycles per secod on the time line, yet all frequencies will cancel if their polarity is inverted.

Simple test: take a complex, non-periodic waveform (a clip of pink noise of sufficient amplitude, a simple spoken voice, or even a strummed guitar chord) and copy it to a second track. Now try phase cancelling the first track by sliding the second track back and forth on the timeline. You can't do it.

You can only, at best, temporarily cancel out certain individual frequencies whose frequencies happen to be related to the given amount of time shift between the two tracks.

G.

 

[chessrock]

Is it just me, or does the guy narrating the clip sound like "Big Gay Al" from South Park?

.

 

[bennychico11]

Now try phase cancelling the first track by sliding the second track back and forth on the timeline. You can't do it.

You can only, at best, temporarily cancel out certain individual frequencies whose frequencies happen to be related to the given amount of time shift between the two tracks.

G.

This is an excellent point, and one this video did not make.
I'm not going to get into the phase versus polarity conversation again since I've debated it to death with people on here...so do a search if you want that
But the author in the video gave a very simplistic definition of what phase is. Yes, of course to make it clearer for inexperienced engineers/musicians...but if he's going to offer "lessons", then certain things need to be brought up. He gave the day to day 'slang' example of what we call 'phase.' In other words:
"That snare is out of phase"

The actual definition of phase was talked about above...a delay in the signal. And how it's measured was not talked about in the video. Also when combining wave forms like the top and bottom snare, the sound of the snare isn't "canceled" out, otherwise we would hear silence if it were. But certain frequencies ARE canceled out. This is important to understanding how phase works. Phase is all around us and within EVERYTHING you record. Not all phase is bad. Sometimes phase relationships of your sound actually give it that certain tonal quality. It's what makes one rooms acoustics sound better than another. I'd say playing in your bathroom versus playing in a symphony hall is an example of GOOD phase.

and...

Is it just me, or does the guy narrating the clip sound like "Big Gay Al" from South Park?

yes

 

[Ethan Winer]

Robert,

So if you take a signal, split it, and send the two identical and phase coherant signals through identical amps to identical speakers, and then reverse the polarity of one of the speakers, aren't the resulting waves 180% out of phase with each other, measured at the same distance from each of the cones?

In addition to Glen's good point about complex waves, your example applies only to one tiny and highly restricted situation. Sort of like all dogs are animals but not all animals are dogs.

--Ethan

 

[The Green Hornet]

Woof Woof Ethan!

You guys are so talented--love to read your stuff.

Green Hornet