Phase inversion button on the pre-amp - what does it do?

Can someone tell me what does the phase inversion button on my pre-amp do. And what is it used for?

 

it inverts the phase, it reverses polarity, it flips the signal, it makes an innie an outie and vice-verse.

It flips the signal to its opposite state, and it is used to correct problems with other devices that problematically flip it etc....

 

English please...

 

If you hear a hum, flip the phase inversion switch and hope it will fix it.

 

Polarity and phase are two different things.

 

Picture the electrical signal carrying the sound as a wave with a series of crests and troughs. Inverting phase will change crests into troughs and vice versa. If something in your playback chain (including the cd itself) is out of phase, it will not sound right. Your woofers will be going in when they should be going out, etc. . . How's that for a non-electrical engineer's explanation?

 

Ooh, you're right. I may have been talking about polarity. I'm not an engineer, electrical or otherwise

 

Is it the same as reversing the wires going into your speakers?

 

Yes, just at a different stage.

 

This article explains the difference between polarity and phase.

http://www.digitalprosound.com/Htm/TechStuff/2000/Nov/SquareOne1.htm

 

Hi James,

First, while the terms are often confused, the correct term for what that button does is Polarity inversion. (Jose, polarity has nothing to do with hum reduction.)

In many recordings and in many components, polarity gets reversed. The button provides a way of correcting this.

So, what is polarity? Musical waves have both positive and negative parts. The positive part of a wave corresponds with an increase in air pressure (or compression, not to be confused with data compression like mp3s use or with dynamic compression used to make records louder - this is compression of the air). The negative part corresponds with a decrease in air pressure (or rarefaction, the opposite of compression).

One key thing to understand about music, that differs from most test signals, is that the waves are asymmetrical. The positive and negative parts are not mirrors of each other. This can be easily seen in any musical waveform, like the type often posted in threads on this forum.

When polarity is reversed by a component or some element in the recording chain, the positive and negative parts of the wave are switched. A compression wave becomes a rarefaction and vice versa. What does this mean for music? (Clark Johnsen wrote an excellent book on just this, called "The Wood Effect".) As with anything in audio, there is much debate and some folks consider inverted polarity inaudible. In my experience, while the ease (or difficulty) with which it can be heard varies from recording to recording, when polarity is reversed, there is a "thin" quality to the timbre of many instruments and an indeterminacy of focus, imaging and soundstaging.

A polarity inversion switch works the same way as reversing the + and - connections on "both" speakers. (This is different from each speaker being wired with different polarity. That is much easier to hear as most bass goes away and images that should appear in the center will seem to be "everywhere and nowhere" at the same time.) The advantage of the button is you can make the change immediately.

I would suggest trying the button with different recordings and seeing if you can notice a difference. (This assumes your system is properly set up to get the best out of it.)

The most recent experience I've had with polarity issues was on the new release of "Revolver". After hearing a thin, somewhat "phasey" sound, I decided to compare waveforms with the CD from '87 ("Taxman" is a good example). These clearly show the two different versions are "upside down" from each other. Reversing the polarity on the new one removed the thin, phasey sound I was hearing, giving it more solidity and focus.

Hope this helps.

Best regards,
Barry
www.soundkeeperrecordings.com
www.barrydiamentaudio.com

 

Phase is achieved through proper polarity, to say otherwise is wrong... tried explaining it, and I would imagine this would be on a per channel basis anyway right?

 

One can have correct polarity and still be off in phase.

I think of phase as being time-based, where polarity is direction(space)-based).

Best regards,
Barry
www.soundkeeperrecordings.com
www.barrydiamentaudio.com

 

Barry - I remember a few cd's being discussed a while ago - that were referred to as "out of phase." Or perhaps they only sounded out of phase. Sorry I don't remember which titles.

Would the feature the OP here refers to correct that issue? Or is that a polarity issue?

I thought polarity had to do with speaker cable terminations, and that was about it.

 

Hi HiFi Guy 008,

While "out of phase" is commonly used, the term isn't technically correct for what it is often used to describe, which is two different things -like the two channels of a stereo- where one has its polarity reversed.

In such cases, where say, the left channel and right channel of a stereo recording or stereo playback system are not in the same polarity, a button like the one in the OP's system won't help. It will reverse polarity on both channels, so one will still be "upside down".

Polarity has to do with the positive part of the wave being positive and the negative part being negative. It is the overall orientation of the wave. Changing the + and - terminal connections at the speakers will reverse their polarity in the same way using a button like the one the OP has. (The button obviously, is easier and faster but they both accomplish the same thing.) Polarity can also be reversed in a lot of audio software packages.

When one speaker mistakenly has its + connected to the amp's - terminal and its - connected to the amp's + terminal but the other speaker is wired + to + and - to -, they are often said to be "out of phase" but the correct terminology is that one speaker has its polarity reversed.

When the two channels are in opposite polarity, the effects are easy to hear. Most of the bass goes away, as does most of anything mixed to the center (often vocals). Images that should appear to come from the center are no longer "solid" but seem to come from "everywhere and nowhere" at the same time. Changing the polarity of one of the channels to match the other will fix this immediately.

Then there is the more difficult to hear issue of both channels being in the same polarity with each other but reversed from the original signal. (I described this and gave an example in my earlier post.) This can occur in the recording, mixing or mastering process. It can also occur in some components, which are said to "invert polarity". And it can occur if the system is accidentally miswired, such as the amp's + terminals being connected to the speakers' - terminals and the amp's - terminals being connected to the speakers' + terminals.

This can be remedied by either reversing the wiring at the speaker, if it is a wiring issue or by using a button such as the OP has, if it is a recording, mixing, mastering or component caused issue.

Best regards,
Barry
www.soundkeeperrecordings.com
www.barrydiamentaudio.com

 

In every test at Stereophile, speakers or components, polarity is mentioned. Extrapolating from this, polarity inversion is possible in components and not just speakers.

 

yep(cool), turning phases too and the worse (for example) : components(circuits) turning phases in 15 degrees(or less...or more) ...can be worse than turning 180 degrees and it really happens.
i posted somewhere here that we have to check "each stage" of the audio with ociloscope to be sure if and where have phases errors...i know is too much and hard ...but i can't think in better idea.

 

Even if one accounted for all inversions in the equipment chain, there is still the issue of how the recording was made. There is no standard at all as to correct polarity, so recordings differ as to absolute polarity.

I have a preamp that allows for phase inversion by remote control, which makes it easier to hear differences in absolute polarity. On some recordings changing polarity seems to make little difference, on the majority, there is some difference but the result is equivocal (for example, the piano may sound less phasey with one polarity, but the vocalist sounds better with the other). For the most part, I stopped bothering with changing polarity. The audibility of a change is also very dependent on the speaker system. On a friend's two-way horn system, the switch is clearly audible and one polarity usually more preferable than another, than on my system.

To best hear the difference, one needs to make a quick A-B type of comparison. Absent a button, and preferably remote control, that is not easy to do. An alternative would be to buy something like the Chesky test CD which has a couple of musical tracks that are repeated in opposite polarity.

 

thank you for the infos, are clevers as always!!
without be obsessed...errr, no way, i'm audio obsessed

here just a few about polarity and absolute phase:
http://www.gcaudio.com/resources/howtos/absolutephase.html

and a little about Wood Effect(and polarity, etc) :
http://www.positive-feedback.com/Issue1/cjwoodeffect.htm

are not so big articles but have good explanations and nobody will be tired or bored, just start and you can't stop to read.
cheers!

 

Er, Steve, reversing a pair of speaker leads *is* changing the polarity

One example where the polarity of something changes - the edit pieces in the "fixed" Deja Vu CD. The polarity of the edit pieces is opposite that of the rest of the CD.

On the original mix of I Looked Away on Layla, the left and right channels of the drums are out of polarity with each other. No way to fix that at home though - if you fix the polarity of the drums, everything else (including the vocals) is wrong.

A good example of a change in *phase* would be the various CSG mixes. One channel is 90 degrees out of phase with the other, resulting in a lack of focus.

 

So the "I Looked Away" drums should mostly disappear when switched to mono? No mono switch on my amp - sorry.
I think Steve is talking about something I've never seen on a modernish amplifier - a single channel polarity inversion switch. The only ones I've seen alter the polarity of both channels simultaneously. What amplifiers had a phase switch, Steve?

 

IIRC, they thin out a bit rather than totally dropping out, since most of the sound of the kit seems to be from the overheads.

 

I believe he meant it would change the polarity of one channel with respect to the other, which should only be needed to correct mis-wiring or a really goofed recording.

For anyone still wondering about polarity, picture this:
- A microphone in front of a kick drum
- The drum is struck and moves towards the microphone
- On playback, your speaker woofer should move towards you
- But if the polarity has been inverted somewhere in the recording chain, the woofer will move away from you.

You could kind of think of polarity as a DC thing (what happens if I connect a battery to the speaker, which way does it move, in or out??), and phase as an AC thing, though that analogy is probably flawed.