When cutting a record, which channel has inverted polarity?

[richard-ec2]

It seems such a simple question but I’ve searched for an answer for a year without success.

When cutting a record, which channel has its polarity inverted?

The reason I ask is:

As far as I know, there is no way on earth for a person with a vinyl playback system to know whether his rig is playing back with the correct absolute polarity. There are test records that will tell the user whether one channel is out of phase with the other but there are no test records I know of that will reliably tell the user whether both channels have the correct polarity or whether both channels are inverted.

So, I’ve been trying to devise a simple polarity test that anyone can use.

All you need, apart from the turntable and a phono stage, is a computer with software that will record a waveform. I use Adobe Audition but anything will do.

My original idea for the test was:

1. Open a new file in your waveform editor and hit the "record" button.

2. With the turntable completely stationary, drop the stylus gently onto a flat area of vinyl such as the deadwax.

3. Look at the spikes you’ve just recorded in your waveform. If the spikes in both channels go up (positive), your polarity is correct. If they go down (negative), your polarity must be inverted.

But as I’m sure you would have told me, this test doesn’t work because, even if your channels are in phase and your rig has the correct polarity, both spikes don’t go up. One spike goes up and the other goes down, because one coil inside the cartridge deliberately has inverted polarity.

What I’ve learned is that this is a feature of the Westrex 45/45 cutting system. The channels cut into in a stereo record have to have opposite polarity, otherwise a stereo cartridge playing a mono record wouldn’t work because the L and R signals would cancel each other out.

So what we have is a cutting head that has one channel inverted. And in order to restore the correct polarity, the cartridge has one channel inverted as well, so the signal coming out of the cartridge has both channels back in the correct polarity.

Now, my simple little polarity test would be fine if only I knew which channel was the right way up and which one was inverted. I suspect that the right channel is inverted, so if someone’s vinyl rig had the correct absolute polarity, the drop test would produce a positive (upward) spike in the left channel and a negative (downward) spike in the right channel. But is that so?

[opcode66]

It technically doesn't matter which is wired in reverse.

[markrob]

Hi Todd,

It does matter if you care about absolute polarity. That's what he is attempting to determine. Does anybody know if there is a standard for this? For example, do all pickup makers internally wire the same way? Has this been established for professional cutting systems? Personally, I don't think its a big deal, but you would think that this has been thought out. The polarity of loudspeakers is, as far as I know, standardized such that a positive voltage applied from the + to - terminals causes the speaker to move outward.

Mark

[gold]

Hi Todd,

It does matter if you care about absolute polarity. That's what he is attempting to determine. Does anybody know if there is a standard for this? For example, do all pickup makers internally wire the same way? Has this been established for professional cutting systems? Personally, I don't think its a big deal, but you would think that this has been thought out. The polarity of loudspeakers is, as far as I know, standardized such that a positive voltage applied from the + to - terminals causes the speaker to move outward.

Mark

I have run into cartridges that were wired reverse polarity from other cartridges. I can't recall which cartridges. Absolute polarity is still a controversial subject. Some maintain it is inaudible. I have heard it make a difference.

I have never heard of a standard for absolute polarity. I maintain absolute polarity through my system. An easy way to check this is to diode clip a sine wave. That way you know the flat top is positive going. The Zuma alignment tape has a diode clipped tone.

[opcode66]

This was my understanding. That there was not an agreed upon universal industry standard. Therefore, it doesn't techically matter. I always make my right channel reversed in Project Bladerunner. Thanks Paul.

[gold]

IIRC on my system the positive going polarity is towards the inner diameter under the microscope. That means it is actually towards the outside of the disk.

[opcode66]

With phono playback cartridges not having a concrete standard, sort of makes that distinction arbitrary.

If facing the cutterhead mounted on a lathe, the right channel transducer is on the left. It cuts into the outside of the groove. Which is consistent with what Paul is saying.

I can tell you that Vinyl Recorders are wired with R out of phase.

[richard-ec2]

I agree that, in practice, it may not matter very much, if at all. Although some people say they can hear inverted polarity, the fact is, the absolute polarity of recorded material both on CD and LP is all over the place - it's very common, for example, to find the CD of a piece of music has the opposite polarity to the LP of the same piece of music. It's really just for peace of mind - if I found I had the positive and negative connections reversed on both my speakers, I would definitely correct them even though it probably wouldn't make any difference, and this is the same thing.

It's interesting to hear the suggestion that there may not be a standard. That would explain why absolute polarity is all over the place. And yet, I still think there may be a standard. On another forum, where quite a few of us did the drop test I described in the OP, we found a fairly high degree of uniformity in the results, with most people finding the right channel was upside down. So I think cartridge makers are mainly - not universally, but mainly - working to a common standard and that's what made me think that cutting engineers must be, too.

I don't know if I'm allowed to link to another forum but if so, here is the discussion:

http://forums.stevehoffman.tv/threads/needledroppers-help-invent-a-polarity-test-by-literally-dropping-your-needles.343492/

[Stevie342000]

AFAIK there was a standard for polarity you could get a polarity checker it was standard practice before it all went digital, it now seems to have fallen by the wayside.

An email to the AES would probably get the definitive answer on exact polarity, there is bound to be a paper on it old or new.

Polarity makes a difference with transmitters or radio stations may affect signal strength, someone more knowledge than me would know the answer, you just need to ask the right question in the right place.

[gold]

AFAIK there was a standard for polarity you could get a polarity checker it was standard practice before it all went digital, it now seems to have fallen by the wayside.

An email to the AES would probably get the definitive answer on exact polarity, there is bound to be a paper on it old or new.

Polarity makes a difference with transmitters or radio stations may affect signal strength, someone more knowledge than me would know the answer, you just need to ask the right question in the right place.

There is a polarity standard as far as balanced signals on xlr cables goes. Pin 2 is +. This doesn't address what's physically on a record. You could make the polarity at the connector "right" even if what's on the record is "wrong". I've seen a lot of the literature on disc recording and I don't recall ever seeing a standard mentioned. FYI the AES has very little on disc recording standards. They were worked out before the AES existed.

[Stevie342000]

Thanks for that but I seem to remember an Ampex tape machine had pin 3 as hot. As for pre-AES the information will be in Audio magazine which was the pre-cursor before the AES, you can find that on at the American Broadcast website: http://www.americanradiohistory.com/Audio-Magazine.htm

So again the standards even as far as professional equipment from back in the day was hit and miss as to which was the hot pin.

A few test discs have in phase and out of phase stereo signal on them, which was the point of the disc so you set absolute phase on your system. Some pre-amps had a phase reversal switch as well. There probably was no standard for phase on stereo discs, the only way to know for sure is to set up your cutting chain checking phase as outlined in previous posts and then to use a test disc to check phase on your replay chain. It's too much bother for most people though. Can you hear it well you should be able to, does it make a difference probably.

[gold]

Thanks for that but I seem to remember an Ampex tape machine had pin 3 as hot. .

The XLR polarity standard wasn't implimented until the 1980's IIRC. The U.S.A. mostly used pin 3 + before that. Europe mostly used pin 2 +. The output of an Ampex 300 was unbalanced on an XLR with Pin 3 hot.

The pre AES standards are held by the Acoustical Society of America.

[gold]

AFAIK there was a standard for polarity you could get a polarity checker it was standard practice before it all went digital, it now seems to have fallen by the wayside.

You can still get "chirpers" for checking polarity from input to acoustical speaker output. Most of the software packages can do this also. Best practices would be to maintain absolute polarity but I don't think it was ever considered important enough to loose sleep over. You need a pretty good system to hear it in the cases where you can hear it at all. I've only heard it on the low end when there is some air moving.

[gold]

the fact is, the absolute polarity of recorded material both on CD and LP is all over the place

We have no idea what was being listened to when it was recorded. If it looks like it's reverse polarity to you but that is what the production team was listening to is it wrong?

With multitrack recording it's really multi mono not stereo. Generally I assume a bass drum hit should make the speaker go out. But who's to say?

[Stevie342000]

Given all that it's a bit of lame duck then really, you could set your system so the polarity is set from the record to the replay chain is correct.

But then when you go to play a record or a cd or radio there is no certainty over the polarity when you listen to those.

Would it be fair to conclude that it is a mess? Would it be correct to assume that there was no issue with polarity when the signal is mono? I am assuming the answer would yes and no. How does the chirper work (thanks for the reminder)?

[gold]

Would it be fair to conclude that it is a mess?

Yes

Would it be correct to assume that there was no issue with polarity when the signal is mono? I am assuming the answer would yes and no. How does the chirper work (thanks for the reminder)?

It's the exact same issue in mono. Does the speaker move out with a positive going waveform or does it go in with a positive going waveform?

[Stevie342000]

Right got it thanks for that, was not sure on mono issue but all clear now.

Is there a simple solution for use when cutting or replaying discs?

[gold]

Right got it thanks for that, was not sure on mono issue but all clear now.

Is there a simple solution for use when cutting or replaying discs?

I think all you can do is follow the manufacturers recommendation. Wire up a polarity reverse switch. Flip it when you play a disk. If it sounds better to you that way leave it.

[Stevie342000]

That sounds like the only viable option to me lacking any adherence to a standard by all, alternatively swap the pair of leads one channel on your cartridge head shell.

[gold]

T alternatively swap the pair of leads one channel on your cartridge head shell.

You would have to reverse the polarity of both channels. If you reverse the polarity of one channel you will hear the difference signal.