Question about phase reversal...

[Robert D]

Ok you flat earthers, please ponder for a moment why balanced cables and their associated I/Os are effective in reducing emi induced noise. What is the principle at work, and why is it effective on noise, not just sine waves?

 

[bennychico11]

What is the principle at work, and why is it effective on noise, not just sine waves?

common mode rejection
it's assumed that the EMI introduced into the signal is introduced equally to both hot and cold (original signal and phase inverted). But both have the same phase and when you invert the cold one again and mix it with the hot one...the two noise signals are now out of phase and will cancel each other out.

 

[Robert D]

common mode rejection
it's assumed that the EMI introduced into the signal is introduced equally to both hot and cold (original signal and phase inverted). But both have the same phase and when you invert the cold one again and mix it with the hot one...the two noise signals are now out of phase and will cancel each other out.

You are correct sir! So when the inversion occures, it is affecting a phase inversion, which is why phase cancellation can be employed to produce common mode rejection. And of course the desired signal is now in phase and so sums rather than cancels.
As I said in the other thread, polarity reversal is the method, phase inversion is the result.

 

[Robert D]

In the strictest sense of the word, you really cannot "invert" phase, and you cannot have "phase inversion"... You can only have "phase shift", i.e. you can move the waveform a tiny bit forward or backward in time.

If people started to differentiate between polarity inversion and phase shift, this whole confusion would go away.

Tell that to all the professors and all the textbooks that teach that the output of a common emitter amplifier is 180 out of phase with the input, that one of the features of a common emitter amplifier is phase reversal. It is not phase shift, it is instantanious phase reversal.

Keep in mind that the term phase does not belong to the audio world, or even the world of electronics.

 

[SouthSIDE Glen]

Polarity reversal is the method, phase inversion is the result.

Phase inversion is *A* result, not necessarily *THE* result.

Polarity inversion results in phahse inversion as one of it's effects. However, phase inversion does not necessarily result in polarity inversion.

Invert the polarity alone, and you effect a phase inversion (as only one of a couple of possible effects). Effect a phase inversion alone and polarity inversion is not guaranteed.

One is a necessary result of the other but the other is not a necessary result of the first. The two are NOT equivalent.

G.

 

[MadAudio]

Glen:

It makes sense now... I completely get it. I'll just invert the bottom snare mic and 2nd kick mic, and adjust from there.

MadAudio:

Here are my kickass Battery pics.....

X/Y above my head

604's on toms:

609 on floor tom:

Another shot of the toms (hard to get a good angle)

All input is welcome. I can't wait until I upgrade to Battery 3.0 (better mics)

Thanks for the pics. Nice looking set-up, IMO. Interesting that you have an e609 on the floor tom. I'm currently using an Audio Technica ATM25 on my 18" floor.

 

[bennychico11]

Phase inversion is *A* result, not necessarily *THE* result.

Polarity inversion results in phahse inversion as one of it's effects. However, phase inversion does not necessarily result in polarity inversion.

Invert the polarity alone, and you effect a phase inversion (as only one of a couple of possible effects). Effect a phase inversion alone and polarity inversion is not guaranteed.

One is a necessary result of the other but the other is not a necessary result of the first. The two are NOT equivalent.

G.

maybe phase rotation should be the word to use? hmmmm.

 

[jrhager84]

Does my setup look like it could be getting any phase delay or anything? The 609 actually works very well on the floor tom. I'm quite pleased, as it wasn't initially what I got it for... Thanks for the input guys....although I think the phase/polarity argument is getting a little too deep for my understanding LOL.

 

[vadoom]

In the strictest sense of the word, you really cannot "invert" phase, and you cannot have "phase inversion"... You can only have "phase shift", i.e. you can move the waveform a tiny bit forward or backward in time.

If people started to differentiate between polarity inversion and phase shift, this whole confusion would go away.

Naw, just take a NPN transistor and a few resistors and you've got yourself a phase inverter. Your collector output will give you opposite waveform of the input signal.

Just a quick walk-through: If your input is low, you will turn the transistor off and your output will be your rail or close to rail (high). Increasing voltage on the base of the transistor, you will turn on the transistor pulling the voltage on the collector down (since now current flows and creates a voltage drop across the resistor on the collector). Your output goes down (not all the way to zero, but down). Now you have your inverted waveform.

If your take your output off of the emitter, output waveform will resemble your input. Either way no lag - all is done simultaneously (if we ignore the propagation delay )

Mathematically all you have to do is just add a negative sign to your waveform and voila! it is inverted. It is true that if you shift phase by 180deg you will also invert the phase (given the waveform has a relatively simple form - sine or cosine are usually good examples). But now your inverted waveform will lead/lag. If you do that in real life you will probably have to sample your waveform and performing phase shift operation before sending it out. Well, now you've just introduced delay... Furthermore, if you have a ripple sitting on a wave, you will probably have to decide whether to phase shift your ripple or the wave the ripple is riding.

When you switch polarity, (mathematically speaking) you basically add that negative sign to the waveform and it inverts your output.

Anyways, listen to Robert_D, he knows what he is talking about. I sense a great engineer in him.


Enjoy your phase inversion!

 

[flatfinger]

Everytime a thread on phase emerges, drums and mics pop up,
(of course!)

I was trying to remember where I read this all those other times and finally did ; Here's some interesting stuff and illustrations in this little pdf from tri-tone digital.


http://www.tritonedigital.com/manuals/TTD_PhaseTone_1_1_Manual.pdf


Quote from page 11 .............

"this is why just shifting a track in your favorite DAW to attempt to time- align several mics rarely produces really excellent results"

What do you guys think of that theory presented there? ; Geeze , digital algoRythms to solve every recording challenge!! Gotta get out the lab coat and test this out soon Every DAW should come equiped with a freak'n slide rule!! I'm goin to phase these phase threads out !

 

[SouthSIDE Glen]

maybe phase rotation should be the word to use? hmmmm.

You miss the point, Ben. Phase change (whether it's "shift", "rotation", "inversion", "flipping", or whatever) is simply not the same thing as polarity inversion, no more than multi-band compression is the same thing as equalization. Period. The two can produce different results in real life which can have different and real effects on both the waveform and the sound.

G.

 

[Robert D]

http://www.tritonedigital.com/manuals/TTD_PhaseTone_1_1_Manual.pdf

Quote from page 11 .............

What do you guys think of that theory presented there? ; Geeze , digital algoRythms to solve every recording challenge!! Gotta get out the lab coat and test this out soon Every DAW should come equiped with a freak'n slide rule!! I'm goin to phase these phase threads out !

I'm definitley going to give this plug a test drive, very cool, thanks for posting it. Here's another variable phase rotation plugin....

http://www.voxengo.com/product/pha979/

 

[SouthSIDE Glen]

Mathematically all you have to do is just add a negative sign to your waveform and voila! it is inverted.

But that inverts it around 0DC; i.e. the 0DC centerline is the "mirror" causing the inversion. Yes there is inversion, but if the waveform is asymmetric, there is also DC shift.

Straight phase change, OTOH, whether it's a 180° shift or rotation or an instantaneous inversion, is relative voltage independant; the waveform mirrors itself instead of using a voltage reference as the mirror.

In waveforms that are not symmetric around 0DC, this makes a difference as it does produce different results.

EDIT: I'm about to run out the door for the day, so I'm out of time for now. But in the meantime I ask all the polarity/phase equalitists to consider the asymmetric wave form and it's RMS vs. crest factor value as well as it's energy distribution by frequency (i.e. it's spectral fingerprint), and how those can indeed be potentially affected differently by a polarity inversion versus a phase inversion only. It's not just DC offset that's at stake here; it's potential differences in the actual sonic character of the signal.

G.

 

[noisewreck]

so is the reversal button on my DAW useless for getting more in phase on "asymmetrical waveforms" as my snare and such?

I wouldn't use the phase button on the DAW to align the top and bottom mics of a snare (for example), at least not by itself. Instead, I'd zoom in real close to both tracks, and manually align them to make sure first of all the attack portions are aligned. Once they're aligned, then if one is 180 degrees off, then I'd engage the "phase"... nee... polarity reverse button on the bottom mic track.

 

[kubeek]

I don´t understand how you can shift DC with inversion. If there is any, it is also inverted, and not shifted. Anyway, DC offset is mostly that low it doesn´t matter.

 

[Robert D]

But that inverts it around 0DC; i.e. the 0DC centerline is the "mirror" causing the inversion. Yes there is inversion, but if the waveform is asymmetric, there is also DC shift.

Straight phase change, OTOH, whether it's a 180° shift or rotation or an instantaneous inversion, is relative voltage independant; the waveform mirrors itself instead of using a voltage reference as the mirror.

In waveforms that are not symmetric around 0DC, this makes a difference as it does produce different results.

EDIT: I'm about to run out the door for the day, so I'm out of time for now. But in the meantime I ask all the polarity/phase equalitists to consider the asymmetric wave form and it's RMS vs. crest factor value as well as it's energy distribution by frequency (i.e. it's spectral fingerprint), and how those can indeed be potentially affected differently by a polarity inversion versus a phase inversion only. It's not just DC offset that's at stake here; it's potential differences in the actual sonic character of the signal.

G.

Glen,
I haven't responded to your last couple of posts because I'm getting my ducks in a row. To some here this may seem like we're (annoyingly) arguing over semantics, but this really is a topic that deserves some study and discussion. I'm glad that we're on opposite sides of the debate, as such, since it forces both (or all) of us to really think about this and not just fall back on our accepted notions of what these terms really mean and how we assume they're being applied both in hardware and software.

 

[Robert D]

I don´t understand how you can shift DC with inversion. If there is any, it is also inverted, and not shifted. Anyway, DC offset is mostly that low it doesn´t matter.

In hardware, most circuits are decoupled so that any DC components aren't passed along. In software, I have no idea if this is done, but if I were writing the module I'd consider making DC offset removal part of the process, preceding the phase inversion.

 

[dachay2tnr]

I'm in the middle now.

Does that mean you cancelled yourself out?




A little polarity humor.

 

[jrhager84]

Well at least one person's helping me in MY thread! *shakes fist at people*

BAH!

 

[Robert D]

Well at least one person's helping me in MY thread! *shakes fist at people*

BAH!

Sorry for the hijack dude.