Finally - an absolute polarity test for vinyl playback!

Up till now, there hasn’t been any way for audio enthusiasts to test the absolute polarity of their vinyl setup. The simple test I’m about to describe will fill that gap.

For anyone who’s not sure what this is all about, it’s about making sure positive is connected to positive and negative is connected to negative, all the way through the audio chain.

In a stereo system, obviously you want the polarity correct in both channels. If it isn’t, there are two ways it can be wrong: either you can have one channel right and the other wrong, or you can have both channels wrong.

The worst case is having one right and one wrong. In this case, the channels are out of phase, which means they’re working against each other and to some extent cancelling each other out. It sounds terrible and for that reason it’s easy to test by ear. The remedy is simple: you reverse the polarity of one of the channels so they’re back in phase again.

But here’s the funny thing. Getting the phase right doesn’t actually mean your channels have the CORRECT polarity. It only ensures that your channels have the SAME polarity as each other! Both may be right - but both may be wrong, and there’s no way a phase test will ever tell you because all a phase test can tell you is whether or not your channels are in phase.

The following test checks whether both channels are right (in which case, your absolute polarity is correct) or whether both channels are wrong (in which case, your absolute polarity is inverted).

All you need is some way of hooking up your turntable to a PC and any piece of software that will show a waveform (a picture of the sound wave coming out of the record player.) Free software is widely available – Audacity is very popular on this forum.

Then follow these steps:

1. Place a record on the turntable but don’t start the turntable. The turntable must be completely stationary at all times during this test.

2. Hit the “record” button in your waveform editor.

3. DON’T start the turntable! Using the arm lift or the fingerlift on the tonearm, carefully drop the needle vertically onto a flat area of vinyl, avoiding any groove. The deadwax is the obvious choice but it’s important to avoid the groove.

4. With the waveform editor still recording, do a few more drops to make sure you’re getting a consistent result.

5. Hit the waveform editor’s stop button and zoom in on your results.​

Result:

If your absolute polarity is correct, then the initial spike each time the needle hits the vinyl should be

UPWARD (POSITIVE) in the LEFT channel

and

DOWNWARD (NEGATIVE) in the RIGHT channel.​

And that’s it! If your spikes go in the opposite direction, then either you have an unorthodox cartridge that doesn’t follow the rules, or something else in your vinyl playback chain is inverting the signal.

By the way, if both spikes go in the same direction, then your channels are out of phase. But your ears should have told you that long ago.

That really is all there is to it. Everything else in this post is just background and you don’t need to read it, though there are a couple of sample test results that you might find helpful if you’re having trouble interpreting your results.

Happy testing! And feel free to post your results.


Background


1. FAQ

There’s just one FAQ. Does absolutely polarity matter?

Answer: it certainly doesn’t matter as much as having your channels in phase. Whether it matters at all is debatable and I’d rather we kept that discussion for another thread.

Personally, I think it probably doesn’t matter but for me it’s just about doing things right. To any sceptics: suppose one day you discovered that you’d accidentally hooked up your speakers with the polarity reversed on BOTH channels (negative going to positive and positive going to negative). Would you put it right, even though you knew it didn’t matter? Of course you would. So, you see, you really do care about absolute polarity!


2. Sample results

Here’s where I talk you through a couple of test results, in case it helps someone.

This is a test I did in Adobe Audition (which isn’t a free program.)






Let’s start from the left-hand end of the waveform. To begin with the, it flatlines, because the needle isn’t in contact with anything. With the turntable stationary, I then drop the needle onto the deadwax using the mechanical arm lift. Because it drops the needle so gently, there’s only a little spike in each channel when the needle hits the vinyl. But it’s big enough to see that the initial spike is upward (positive) in the left channel and downward (negative) in the right, which is as it should be.

I would emphasise that it’s the initial spike you need to look at, when contact is first made – don’t be put off by the following squiggles as the needle bounces back. You can see in the waveform that my needle bounces about a little before settling down. Then suddenly – POW! At the right-hand end of the waveform, there’s another pair of spikes, big ones this time, and both in the wrong direction. What happened? The answer is that this where I lift the needle off the deadwax again, so the needle moves in the opposite direction – instead of being squashed upwards, it’s released downwards. At this point, you would expect the spikes in the waveform to go in the reverse direction, and sure enough, they do.

Here’s another test but this time, instead of using the mechanical arm lift, I used my finger and dropped the needle rather more abruptly onto the stationary vinyl:



From the left, here’s the story. First, you see a flat line because the needle isn’t in contact with anything. Then I drop it onto the vinyl and you can see that the initial spike, quite large this time, is upward in the left channel and downward in the right, so that’s correct. Straight away the needle bounces back so you tend to get an “echo” spike in the other direction, and you can also see a bit of wobbling or vibration in the right channel until we reach the second spike, which is where I lift the needle off the vinyl again. As you’d expect, the spikes this time are reversed.

There’s then a moment of flatlining while the needle isn’t touching anything. I then repeat the drop-and-lift, so you get an initial pair of spikes in the correct direction as I drop the needle onto the vinyl, and finally – oops, I don’t know what went wrong there – I must have nudged the needle sideways as I did the lift. In any event it’s a complete mess and doesn’t give the expected result. That’s why we do lots of drops so we can be sure which ones are normal and which are the outliers to be discarded.


3. Theory behind the test

In audio, the convention is that a positive signal corresponds to compression or “push” and a negative signal corresponds to rarefaction (the opposite of compression) or “pull”. So, for example, the skin of a bass drum being pushed towards you should create a positive signal at the microphone which should remain a positive signal all the way through the recording and playback chain until it ends up in your home with the cone of your speaker being pushed towards you, just as if it was the skin of the drum.

About a year ago, when I first thought of trying to devise a test of absolute polarity for vinyl, I thought it would be simple. In line with the convention, I thought, a compression of the needle against the cartridge body would obviously produce a positive signal in both channels. So all I had to do was drop the needle on the vinyl and check that I got positive (upward) spikes in both channels in a waveform editor.

To my dismay, it didn’t work. Sure enough, I got a positive (upward) spike in the left channel - but I got a negative (downward) spike in the right channel. I couldn’t understand what was happening so I started a discussion here:

Needledroppers - help invent a polarity test by (literally) dropping your needles

The answer turned out to be as follows.

It all goes back to the invention of the stereo audio cartridge. At that time, all the records people owned were mono, so the inventors of the new stereo cartridge had to design a cartridge that correctly played back not only the new stereo records but also the existing mono records. Their solution looked like this:



Some people think that, in a stereo record groove, one channel is vertical and one is horizontal. But as you can see from the diagram, that’s not so. If the channels were arranged in that way, they wouldn’t be symmetrical because of other forces such as gravity and the skating force acting unevenly on the two planes. So, to keep them as nearly symmetrical as possible, they are rotated through 45 degrees.

But the crucial element of this arrangement is the polarity of the two coils, which I have marked prominently in the diagram. As you may know, in stereo, the outer wall of the groove represents the right channel. Therefore the coil reacting to the hills and valleys in the outer groove wall is the right channel coil. In the diagram, this is coloured red and marked “Right”.

Now, as you can see from the diagram, there is something odd about this coil – its polarity is inverted. Instead of having positive at the top and negative at the bottom, as the left channel coil does, it’s upside down.

With this is mind, let’s pause for a moment to consider what happens if you move the needle in various directions. An understanding of this is essential to all that follows. If you look at the diagram, specifically with regard to the polarity of the coils, you’ll see that:

1. If you push the needle upwards, you get a positive signal in the white (left) channel and a negative signal in the red (right) channel.

2. If you push the needle to the right, towards the record rim, you get a positive signal in both channels.

3. If you pull the needle downwards, you get a negative signal in the white (left) channel and a positive signal in the red (right) channel.

4. If you push the needle to the left, towards the record centre, you get a negative signal in both channels.​

All clear? Good. Then let’s carry on.

As we just noted, there’s something very odd about the right channel coil – it’s upside down. The reason it’s upside down is because if it wasn’t, you’d be unable to play mono records with a stereo cartridge.

To explain, just suppose that the right channel coil was the right way up, with positive at the top. Now imagine that a mono record is playing on the turntable. With a mono record, the groove only moves in the horizontal plane. So, if you had both coils the same way up, every time the needle moved to one side or the other, it would create a positive signal in one channel and a negative signal - equal but opposite - in the other. In other words, the channels would cancel each other out. So the mono record would be unlistenable.

The solution? A convention was agreed whereby the right channel in a stereo cartridge would be inverted.

But wait, you say. That might fix your mono playback - but surely it wrecks your stereo playback? Because, of course, your two stereo channels are now out of phase.

Well, you’re absolutely right. Or you would be, if not for one thing.

To make this work, it was also agreed that all stereo records would be manufactured (cut) in such a way that the right channel would always be inverted. So, the right channel signal would be inverted by the cutting lathe - only to be inverted AGAIN by the cartridge - and therefore, by the time the signal came out of the cartridge, it would be back the right way up again and everything would be in phase.

Ingenious, isn’t it? And hardly anyone knows this because all the knowledge has been lost and none of it’s on the internet and that’s why it took me forever to get it all confirmed.

But there we are. That’s why one coil in a standard stereo cartridge is inverted relative to the other and that’s why, when you do the drop test described at the top of this thread, you get a positive spike in the left channel and a negative spike in the right.

As you’ve probably figured out already, you don’t have to do the test my way. Now you share the secret knowledge of the coils, you can, if you prefer, push the needle horizontally towards the rim, knowing you can expect a positive signal in both channels. Or you can place the needle on a stationary record surface and suddenly lift up the arm, knowing that the sudden downward release of the needle should produce a negative (downward) spike in the left channel and a positive (upward) spike in the right. Or you could push the needle horizontally inwards towards the centre… never mind, you get the idea.

 

Just one question: If you're connecting just the turntable to a computer, doesn't that eliminate the rest of the audio chain from the test?

 

I remember a whole long thread on this concept a couple years ago, but it seems to have vanished mysteriously.

 

Link is in the post.

 

Well, the idea of this test is just to check the vinyl playback section of the chain because that's the really difficult bit that's been impossible to test until now. Everything else can be tested by other means.

 

Yes, as jupiterboy says, you're probably thinking of the other thread I started a long time ago (and to which you made some valuable contributions!). There's a link to it above but here it is again:

Needledroppers - help invent a polarity test by (literally) dropping your needles

 

as David Bowie and Mick Jagger could teach us: no absolute polarity test can give you a meaningful result.

 

Doggedly researched, brilliant (with no little credit going to all who have participated with you through time), and exactingly thorough. My hat is truly off to you.

 

Many thanks indeed, darkmass, much appreciated. And yes, many people helped, as can be seen on the other thread. I salute them!

 

I did this test and it indicates my TT has reversed absolute phase. I then checked the phase of my Playstation 1 I'm using as a CD player by playing a CD track and comparing it to the ripped track. The PS1 is also reversed absolute phase. So I started thinking my Pioneer SA-1040 amp they are running through is doing something. I then test the iPod I have hooked to the amp via a dock and it showed the CD track in correct absolute phase. That means the TT and PS1 are incorrect unless the amp is reversing it. I give up on absolute polarity of my playback. I'll just reverse any needle drops I do to correct the TT so the source is at least correct.

Btw, unless I made a mistake, it looks like my Metallica Justice vinyl (US, not a re-issue) has opposite phase to the original US CD.

 

How weird! Let me see if I've got this right:

1. The drop test shows your TT has inverted absolute phase.

2. You rip an LP track on your turntable and rip the same track on CD through your PS1 and they come out the same way up.

3. You play the same track on your iPod and it comes out the opposite way up to the LP and CD track.

My thoughts would be:

If your TT is inverting, but you get the same result from your PS1, that means one of two things - both of which you're already suggested. Either your Sony PS1 is inverting too, which wouldn't surprise me all that much since my Sony SCD-XA5400ES SACD player inverts absolute polarity. Or, it's possible that the CD version of the album has opposite polarity to the LP version - this is very common in my experience.

The only way to find out for sure is to do a polarity test on your PS1. The way I would do this is to load a blank CD into your PC and record an asymmetric waveform onto it, remove the CD, put it into your PS1 and play it back, record the output from the analogue or digital outputs of your PS1 and see if the signal comes out the right way up or not.

I'm not sure what your source is for the track you're playing back on the iPod so it's harder for me to comment on that. Are you playing back a digital download of the track, or a rip done on your PC, or a recording done from your PS1?

Also, I'm not sure what you mean about the amp. Surely nothing goes through the amp if you're recording to your PC? Or maybe you've got everything hooked up to the pre-amp and you have an output running from the pre-amp to your sound card - that would make sense. If that's the case, you can easily find out if your pre-amp is inverting by recording something with the pre-amp in the chain and then recording the same thing without the pre-amp in the chain and seeing if they come out the same way up or not.

If you want to get to the bottom of this I'll be happy to help but I'll easily understand if you can't see the point!

 

This is all fine and dandy but there is one problem, and that is that most records aren't made with absolute polarity in mind. This is especially true in multitrack production where many sounds are uncorrelated. There are so many places in the recording chain where the signal can be inverted and when one goes through many active sections, maintaining absolute polarity becomes difficult.

What we usually end up with is recordings with different absolute polarities for different instruments. In other words, the bass may have one polarity and the kick may have another. Which one do you prefer when listening back?

Last month my audio partner sent me a test, as he frequently does. I had to listen to two different samples and determine what was different. I had no idea what he had done if anything. When I listened, I heard differences between the two sample songs quite quickly. The sample I preferred had more impact and better focus, but some things on the other version sounded more realistic, and the more I listened the move obvious the differences were.

Well when I reported my results they were the same as his. When he told me the difference I was shocked. All he had done was to change the absolute polarity.

 

Having a switch on my amp gives me similar experiences—certain instruments or tracks are switched. I even recall someone writing that an instrument could be switched on purpose to spread it's voice out within the soundstage. Anyway, I note those that sound better or more cohesive with inverted phase, and then go back later to see if my perception holds. I'm happy to have the choice, because prime candidates are always those records I like, but that sound a little hazy or indistinct. They are usually the ones that snap into focus when you invert the phase.

 

If I did the drop test correctly, then yes, my TT reverses polarity. I was surprised to find it was reversed as it's a P-mount, so there are no wires which could be mixed around. When I first noticed that it was recording songs in opposite polarity from my last TT (standard mount), I assumed my last one was incorrect and that I must've messed up installing it (no longer have it to check). Doing the polarity test indicates the one I'm using now is the incorrect one.

When I discovered the TT was showing as reversed, I wanted to check everything else I run through the amp in case the amp was reversing everything and that way I could just reverse the speaker hook ups to compensate on playback. When the PS1 also showed reversed polarity, I thought I was onto something about the amp reversing them. Then the iPod was correct and shot that. As you suggest, my next step is to check the PS1 and iPod hooked straight to the PC to see if this changes anything. I don't have the right hook ups right now to do that. Also, I don't have another phono preamp to try, but I will try recording the straight output of the TT once I get hookups.

My PS1 test was done by comparing CD playback to the same CD ripped to wav with XLD. The two did not match.

The iPod test was done using the same ripped CD track. They matched.

If I did all these tests correctly, it shows that the Metallica LP & CD were pressed with opposite polarity.

I don't know if I can hear polarity differences or not, but I'd prefer to have my system setup properly. I just don't know if it's possible, since some of my components reverse it and some don't. My amp doesn't have a switch to compensate.

 

It's quite a puzzle you have there. I think the key is to eliminate the amp because that's introducing a huge uncertainty at the moment. Just trying to think it through, it seems that:

1. If the amp is inverting everything, then your TT is in fact correct and your PS1 is also correct (and the CD and LP versions of this album have opposite polarity, which is very common in my experience). However, your iPod would be inverting, which seems a bit odd.

2. If the amp isn't inverting, then your TT is inverting AND your PS1 is inverting, which is quite a coincidence, but your iPod is in the clear.

As I say I think the best thing would be to eliminate the amp so you know exactly where you stand. In the meantime, maybe you could at least plug the iPod directly into the PC and get a result from that?

 

I know what you mean but for me, this is just about getting your home audio system set up correctly rather than incorrectly. Once you've done that, it may well be that you'll want to invert the polarity of some recordings and not others, but at least you'll know your default position is correct - then, if you tell someone else that such-and-such a recording sounds better with absolute polarity inverted, you'll know for sure you're not inadvertently saying the opposite to what you mean.