[Housteau]

I was curious if anyone here could tell me why some manufacturers allow their components to invert polarity.  Is there actually a technical or design reason why this would be an optimum way to build a circuit?

[Steve Eddy]

I was curious if anyone here could tell me why some manufacturers allow their components to invert polarity.  Is there actually a technical or design reason why this would be an optimum way to build a circuit?

It's often to do with the circuit(s) they choose to use.

A single stage amplifying circuit, such as a single tube or transistor in common cathode/emitter mode has an output whose polarity is inverted with respect to the input. So if you want to use a very simple amplification circuit such as this, then your output's going to be inverted with respect to the input unless you add either another inverting circuit or use a transformer input or output which can invert the signal.

Some would rather go with the simple circuit because they feel it sounds better and then just have the end user flip the polarity of their speaker cables.

Another example would be that current output DAC chips often have an inverted output. This is because they're intended to be used with active current-to-voltage converters which are typically based on an opamp using the opamp's inverting input, which would then give you the "correct" polarity at the output. However if you use passive current-to-voltage conversion, such as a resistor which doesn't invert polarity, then your output's going to be inverted.

I put "correct" in quotes because there are those who argue that there's no standard for absolute polarity on recordings and some recordings may preserve absolute polarity, while others may not, and still others may have a mix of polarities on the same album or even the same song.

Their solution would be to not worry about what the electronics are doing as long as you have a switch which you can use to select the proper polarity for a given recording.

se

[Kevin Haskins]

Don't get me started.....

[Steve Eddy]

Don't get me started.....

Y'already are, so might as well finish it up. C'mon, let's hear your rant.

se

[Housteau]

It's often to do with the circuit(s) they choose to use.

Wouldn't it be just as easy for them to switch it back after their circuit design right at the output jacks?  In that way the unit would at least output the polarity that went into it.

[Steve Eddy]

Wouldn't it be just as easy for them to switch it back after their circuit design right at the output jacks?  In that way the unit would at least output the polarity that went into it.

Piece of cake if it's a balanced output circuit. But if it's single ended, you either have to add another inverting stage or use a transformer.

se

[*Scotty*]

Ah,no. The signal, whether it has a positive or negative polarity always has a voltage potential with respect to ground and cannot be connected in reverse to a jack to alter its polarity.
Doing so merely shorts the signal to ground resulting in no output and may damage the amplifying circuit.
Scotty

[fmw]

I was curious if anyone here could tell me why some manufacturers allow their components to invert polarity.  Is there actually a technical or design reason why this would be an optimum way to build a circuit?

I assume they do it to pander to the audiophile community.  I even have some CD sets with the same content on two CD's with opposite polarity, so others besides amp manufacturers do it also.  I'm pretty sure no one has ever heard a difference in polarity in a properly conducted blind test.  So it would be one of those "belief" things.  Is there a technical reason for it?  I don't believe so.

[Ethan Winer]

Y'already are, so might as well finish it up. C'mon, let's hear your rant.

How about my rant?

Recording an electric bass by plugging it direct into the console is a common recording technique. But what is the correct polarity for that? What if the bass player uses a pick and picks some notes up and others down? There's no standard I'm aware of for pickup winding direction either, so this complicates it further. And what about all-electronic instruments like synthesizers?

Because of the way so much music is recorded these days, it is likely that the absolute polarity of any given instrument in a complex mix is random and unrelated to the absolute polarity of other instruments. In other words, there are more important things to worry about.

BTW, I've tested this extensively and never found a meaningful difference. A few years ago an engineer friend sent me a file with a static sawtooth wave that reverses polarity in the middle. Son of a gun you can hear the timbre change halfway through! But the wave is at 20 Hz, so what's really being heard is loudspeaker nonlinearity. When you try the same test at 50 Hz or whatever your speakers can actually reproduce, all of the sudden the reversal is no longer audible.

--Ethan

[opaqueice]

I assume they do it to pander to the audiophile community.  I even have some CD sets with the same content on two CD's with opposite polarity, so others besides amp manufacturers do it also.  I'm pretty sure no one has ever heard a difference in polarity in a properly conducted blind test.  So it would be one of those "belief" things.  Is there a technical reason for it?  I don't believe so.

Steve Eddy has just explained the technical reason for it.  And in fact it's very easy to hear polarity differences blind - I've done it myself using a PC-based ABX program and cheap headphones, 10/10 correct - if you construct a test signal designed to accentuate the differences (which I did).  It's extremely difficult on music, but I do know of two successful ABX trials using carefully chosen short musical selections.

The reason it's so difficult is that when music is mixed from a recording made on multiple mics at different locations with multiple sound sources, there simply is no such thing as correct polarity, and in addition the differences between the two polarities become very small.

[ted_b]

I was curious if anyone here could tell me why some manufacturers allow their components to invert polarity.  Is there actually a technical or design reason why this would be an optimum way to build a circuit?

I assume they do it to pander to the audiophile community.  I even have some CD sets with the same content on two CD's with opposite polarity, so others besides amp manufacturers do it also.  I'm pretty sure no one has ever heard a difference in polarity in a properly conducted blind test.  So it would be one of those "belief" things.  Is there a technical reason for it?  I don't believe so.

???  Have you not been reading these responses.  Polarity inversion is not a pandering thing, it's caused by simple straight-wire-with-gain approaches to analog circuits, usually tube, and to invert polarity back is to ask the purist designer for more parts in the signal path.  It is a byproduct of the design, not a designed outcome.   It is a fact, though; polarity is in FACT inverted in these designs.  Now, putting a phase/polarity switch in could be consider "pandering" but I myself (ask Dan Wirght, I'm the one who insisted he add it to his preamps) can hear absolute phase changes on some minimalist (single mic) recordings.  On multi-miked, multitracked recordings it's impossible because hundreds of steps were taken in the recording process, and any or all of the mics and consoles could have flipped polarity many times during the signal path.; too many combinations.

I think it's like being able to see the rainbow effects in DLP projectors, or being susceptible to motion sickness...some people are affected, some aren't.  But to say there is no technical reason?  As Charles Hansen said "you're new to this, aren't you"?

[opaqueice]

BTW, I've tested this extensively and never found a meaningful difference. A few years ago an engineer friend sent me a file with a static sawtooth wave that reverses polarity in the middle. Son of a gun you can hear the timbre change halfway through! But the wave is at 20 Hz, so what's really being heard is loudspeaker nonlinearity. When you try the same test at 50 Hz or whatever your speakers can actually reproduce, all of the sudden the reversal is no longer audible.

On a sawtooth wave, yeah, that's speaker non-linearities.  What you need is an honest asymmetrical waveform (I can post one if you're interested).  Using that I was able to prove that the effect I was hearing could not be due to speaker effects (I'll explain how if you care).  I believe it has to do with an asymmetry in how the inner ear responds to rarefactions versus compressions, which is something well-known to physiologists that study hearing.  Very roughly speaking the ear acts as a half-wave rectifier, so asymmetrical waveforms sound different when inverted.

But for normal music, forget it.  You're correct that electronic instruments don't have a correct polarity, but the same applies to acoustic instruments.  A plucked string has one polarity on one side and the opposite on the other side.

[fmw]

I think it's like being able to see the rainbow effects in DLP projectors, or being susceptible to motion sickness...some people are affected, some aren't.  But to say there is no technical reason?  As Charles Hansen said "you're new to this, aren't you"?

Pretty new.  I've only been involved in audio for about 50 years.  Those who are "affected" don't understand the placebo effect that affects us all.

[ctviggen]

I assume they do it to pander to the audiophile community.  I even have some CD sets with the same content on two CD's with opposite polarity, so others besides amp manufacturers do it also.  I'm pretty sure no one has ever heard a difference in polarity in a properly conducted blind test.  So it would be one of those "belief" things.  Is there a technical reason for it?  I don't believe so.

Steve Eddy has just explained the technical reason for it.  And in fact it's very easy to hear polarity differences blind - I've done it myself using a PC-based ABX program and cheap headphones, 10/10 correct - if you construct a test signal designed to accentuate the differences (which I did).  It's extremely difficult on music, but I do know of two successful ABX trials using carefully chosen short musical selections.

The reason it's so difficult is that when music is mixed from a recording made on multiple mics at different locations with multiple sound sources, there simply is no such thing as correct polarity, and in addition the differences between the two polarities become very small.

I have a CD where they have two (or three?) songs.  The took each one of these songs and (digitally) reversed the polarity.  Thus, the CD has both versions -- "regular" and "inverted" polarity.  I spent about 45 minutes listening to these songs over and over and over.  I could not tell a difference.  Every time I thought I heard a difference, I'd switch to the next song (inverted in polarity from the song I just played), and the difference wasn't there. 

The problem I have with polarity is that some amps have inverted polarity and some don't.  For a HT system, that's problematic, as I have to remember that my Jeff Rowland amp that runs my R/L speakers is reversed in polarity but my Bryston 9B or Tube Amp or Nuforce amp, which runs my center and/or rear speakers, is not.  Thankfully, Avia has test tones to discern if speakers are phased properly.

[Steve Eddy]

How about my rant?

Well, since that lazy Kevin Haskins won't finish what he started, rant on.

Recording an electric bass by plugging it direct into the console is a common recording technique. But what is the correct polarity for that? What if the bass player uses a pick and picks some notes up and others down? There's no standard I'm aware of for pickup winding direction either, so this complicates it further. And what about all-electronic instruments like synthesizers?

Actually this whole polarity thing centers around the preservation of "absolute polarity" as it relates to an original acoustical event. Simply put, the compressions/rarefactions that occur and were recorded at the original acoustical event should be preserved such that upon reproduction, what were originally compressions remain compressions and what were originally rarefactions remain rarefactions.

When it comes to electronic instruments which go straight into the console, I guess it's every man for himself.

se

[Steve Eddy]

The reason it's so difficult is that when music is mixed from a recording made on multiple mics at different locations with multiple sound sources, there simply is no such thing as correct polarity...

Actually there is.

Acoustical waveforms are made up of compressions and rarefactions. That doesn't change simply because you have multiple microphones at different locations. You can only change that electronically somewhere between the microphone and the loudspeaker.

se

[John Casler]

Hi Dave,

To answer your question:  My Bryston BP26 preamp has a "phase" switch, which I beleive to be the same thing.

I cannot say, I have heard the difference, but then I haven't really made the effort to do any large scale A/B.

But I do see the Rainbows and I did get sea sick on my last Ocean Cruise (in Tahiti) but was saved by the "patch" until I aquired my "sea legs".

[Kevin Haskins]

You can move the mic, just a couple inches, correct for SPL electrically and whola!   The waveform that used to be making an electrically negative waveform is now making a positive one.     Which is correct?  Which is absolute?

Now use multiple microphones, mix the music through an unknown amount of signal processing, the recording engineer plays it back through a "studio monitor" which has its own effect on the phase.   So.... tell me, what is absolute about any of this?   Which phase is right and which is wrong and how do you determine this?

It may be helpful for many people who do not understand the terminology to look at an analogy.   Imagine your in the middle of the Pacific Ocean.   The waves hit your boat in a manner where there are peaks and valleys.   If you move  your boat, forward or backward relative to your original position your boat will move in a different manner than the original boat.   But... from the position of both boats the wave motion feels the same.   The fact that one moves up or down different from another is of no consequence.   Which of these motions is correct?   Which of these are absolute?   Would you yell over to the other boat, "hey... get your motion correct, your bobbing up and down at the wrong time relative to the absolute motion!!".   

This is a simplification because there are other things that change with microphone position, (relative SPL of the waveform, reflections and cancellations etc..) but its a good brain exercise to think about the subject.

[Steve Eddy]

You can move the mic, just a couple inches, correct for SPL electrically and whola!   The waveform that used to be making an electrically negative waveform is now making a positive one.

Well, not quite. At least not once you go beyond perfectly symmetrical waveforms like a simple sinewave, which aren't particularly representative of the waveforms produced by musical instruments.

Yeah, if you've got a nice symmetrical waveform, it really doesn't matter. But consider an asymmetrical waveform. Say, an impulsive waveform with an initial attack which is acoustically compressive (which we can analogize as electrically positive). The compressive nature of that initial attack will remain compressive no matter what the distance the microphone is from the source. And the compressive nature of that initial attack would be the "absolute polarity" of that waveform.

And it is the goal of the proponents of preserving absolute polarity that when that waveform is reproduced at your speakers that you end up with an initial attack which is compressive rather than rarefactive.

se

[fmw]

I assume they do it to pander to the audiophile community.  I even have some CD sets with the same content on two CD's with opposite polarity, so others besides amp manufacturers do it also.  I'm pretty sure no one has ever heard a difference in polarity in a properly conducted blind test.  So it would be one of those "belief" things.  Is there a technical reason for it?  I don't believe so.

Steve Eddy has just explained the technical reason for it.  And in fact it's very easy to hear polarity differences blind - I've done it myself using a PC-based ABX program and cheap headphones, 10/10 correct - if you construct a test signal designed to accentuate the differences (which I did).  It's extremely difficult on music, but I do know of two successful ABX trials using carefully chosen short musical selections.

You are on a different subject.  Let's keep things on track.  The OP asked about polarity switches on amplifiers.   He's wondering what benefit it provides to his listening.  If you think you can tell which way the polarity switch is set on an amplifier by listening to any music in a properly conducted blind test, I'd be happy to put up some money as a bet that you can't.  How do I know?  I've done the tests many times with many audiophiles.  Polarity isn't audible in music.  You can believe it is as many do, but it isn't.  The polarity switch is just an audiophile "feature" with no real world purpose except, perhaps, to play with "specially designed test signals" designed to point out the polarity.