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spauzano
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Inverting polarity

My current DAC allows me to invert polarity. I've found that inverting polarity has a significant effect on certain CDs while little on others. I'm very careful with all connections in my system and do not think there's a problem with the hardware. I do not see a trend happing either, it's not like 90% of my collection sounds better inverted or not. I find that I have to check it CD to CD.
Most of my collection is rock with some acoustic artists in the mix.
Does anyone else run into this on a regular basis and would anyone be able to point out manufactures that allow inverting on thier equipment? Thanks

Elk
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Re: Inverting polarity

There are quite a few that find changing absolute polarity can make a difference.

There are a number of preamps that allow one to switch polarity, even by remote, but I don't have a list of them. Others here are quite good on identifying equipment with certain characteristics however.

What DAC are you using that provides this feature?

spauzano
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Re: Inverting polarity

An old Audio Alchemy V2.0 with the accompaning DTI.Both invert and of course I make sure both are in sync.

dcstep
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Re: Inverting polarity

My Rowland Continuum 500 integrated amp has such a feature. Generally you'll notice it the most where the music has a very distinct push-pull type of percussiveness, like a closely miked kick drum or the bass drum whacks on the Reference Recordings Holst Suites for band. Once you've heard it, then you can hear it in a broader range of music. The Sheffield Labs "Drum Record" has a track or two, where if you can't hear it there, you'll never hear it.

I've found that setting polarity with a test record and just leaving it works fine for me. Some people, realizing that all recordings are not made with the same polarity, try to listen on each LP or CD and switch it from recording to recording. That's overkill for me, however, if I ever notice things sounding a little indistinct or lacking expected impact, I punch the ole polarity switch and, much of the time, it improves things.

BTW, without such a switch, then you have to switch the speaker cable leads, a true pain in the butt. It is worth getting right in system set up and if you do it with a test recording, then you'll be right most of the time, IME.

Dave

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Re: Inverting polarity


Quote:
I've found that inverting polarity has a significant effect on certain CDs while little on others.


I've experimented with this, and concluded that when absolute polarity makes a difference - and sometimes it does - the cause is loudspeaker nonlinearity at low frequencies. That is, it's not that absolute polarity is actually audible, but that some loudspeakers distort differently pushing outward versus drawing in.

--Ethan

Elk
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Re: Inverting polarity


Quote:
I've experimented with this, and concluded that when absolute polarity makes a difference - and sometimes it does - the cause is loudspeaker nonlinearity at low frequencies. That is, it's not that absolute polarity is actually audible, but that some loudspeakers distort differently pushing outward versus drawing in.


That's the best explanation that I have seen as to why there is an audible difference.

It makes no sense to me that we can distinguish polarity. Even a bass drum thwack is around 40hz. Once the sound wave starts its going both directions so we can't hear a difference here. Thus, the only opportunity we have to hear a difference is first half of the wave; that is, 1/80 of a second of push v. pull. This isn't transient information - it is the sound's fundamental. How can it matter which direction the wave starts if the equipment one is listening to reproduces both accurately?

Ethan, in the recording I have done and otherwise have witnessed, no one reverses polarity - although it is easy to do so. I am unaware of any analog or even digital outboard devices that do so. Any explanation as to where/why polarity gets reversed on some recordings?

struts
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Re: Inverting polarity

Elk,

It's down to the way you design your output stage. Some designers would rather just stick a warning in the manual saying that the piece inverts polarity (which can easily be corrected at the speaker terminals) rather than have to add an additional output stage to correct it. You'll generally therefore find this in more 'minimalist' designs where circuit simplification has been the priority.

Elk
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Re: Inverting polarity

Yes.

But I haven't seen polarity reversal in studio equipment or in recordings I am involved in. I don't get why some recordings have different absolute polarity.

dcstep
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Re: Inverting polarity


Quote:
I don't get why some recordings have different absolute polarity.

I think it was to do with certain devices inverting polarity (why I don't know). My Conrad Johnson CA200 amp inverted polarity and told you so. If you string together two devices that invert polarity, then you didn't invert at the end; however, if one device inverts and the other doesn't, then you inverted polarity. Put more devices in the stream and then you have more chance to invert (or not).

Dave

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Re: Inverting polarity

I'm not really up on pro audio/recording equipment but I guess I thought this was a mostly a legacy issue from the valve era. Are there any modern (i.e. DSD-era) labels/studios currently producing polarity inverted discs?

Kal Rubinson
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Re: Inverting polarity


Quote:
That is, it's not that absolute polarity is actually audible, but that some loudspeakers distort differently pushing outward versus drawing in.
--Ethan

It's the Clinton effect.

Kal

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Re: Inverting polarity

A single stage of amplification may consist of one device such as a transistor or tube, or it may consist of several cascaded together. Depending on its configuration, each may be inverting, so that two inverting devices together would be non-inverting. Some manufacturers prefer not to add an extra device to "correct" the polarity of the amplifier due to cost, or because they feel the additional device adversely affects the sound. Some don't tell you whether or not their product inverts polarity. This applies to microphone preamps, mixing consoles, preamplifiers, and so on. Great care must be taken to insure absolute polarity, or it may happen by chance. Considering how few people may notice, or care, it isn't surprising that most recordings are produced without regard to absolute polarity.

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Re: Inverting polarity

I'm quite sensitive to phase, having designed more than a few speaker crossovers..but..it tends to be such a headache when the phase is so rarely maintained in multi-track recordings..so I don't bother much, as far as worrying goes.

Sometimes,when first setting up a given system ..I'll check it out with either a soundcard (oscilloscope program and y cables) or a oscilloscope (and signal generator and y cables)..when I first set a given system up.

If I can be bothered to be curious enough.

RGibran
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Re: Inverting polarity


Quote:
Does anyone else run into this on a regular basis and would anyone be able to point out manufactures that allow inverting on thier equipment? Thanks

PS Audio Control amplifiers have a phase switch on the remote. Helps discern the difference when you can activate the change from the listening position although I admit to almost never fidling with it.

RG

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Re: Inverting polarity


Quote:
That's the best explanation that I have seen as to why there is an audible difference.


This is from my Audio Myths article:


Quote:
Mike Rivers from Recording magazine sent me a test Wave file that shows absolute polarity can be audible in some circumstances. The polarity.wav file (87k) is a 20 Hz sawtooth waveform that reverses polarity in the middle. Although you can indeed hear a slight increase in the low end fullness after the transition point, I'm still not 100 percent certain what this proves. I suspect what's really being shown is a nonlinearity in the playback speaker, because with a 50 Hz sawtooth waveform there is no change in timbre.


Since the change in timbre on Mike's wave file no longer happens at a higher low frequency* within the speaker's linear range, I'm pretty sure the effect is due to loudspeaker nonlinearity, and not evidence that absolute polarity is actually audible.

(*is higher low frequency an oxymoron? )


Quote:
Ethan, in the recording I have done and otherwise have witnessed, no one reverses polarity - although it is easy to do so.


Heh, that sounds like DUP when he points out that you never see expensive cables on cable elevators at a live concert with pro sound engineers.


Quote:
Any explanation as to where/why polarity gets reversed on some recordings?


Actually, if you think about it, many instruments don't even have an absolute polarity to honor. For example, an analog synthesizer creates waveforms that generally fade in at some rate based on the ADSR settings. And an electric bass connected direct has no real polarity since you can pluck the string up or down. Same for an electric guitar through an amp. Yes, there will be an initial direction, but it's irrelevant and the waveform is mostly symmetrical anyway.

The only time absolute polarity matters is when multiple microphones are used on a single acoustic source, to avoid comb filtering cancellation. And all recording pros know that when you mike a snare drum from the top and the bottom, you must reverse the polarity on one of them to avoid the same cancellations.

--Ethan

Elk
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Re: Inverting polarity

Excellent post, Ethan. Good stuff to ponder.

I had not considered that many instruments do not have established polarity. I am now curious to go through my collection of instruments and record repeated notes to see if the polarity remains constant. I bet it doesn't.

What happens with 'cello? If you play a series of quarter notes, for example, does each note either start with a rise or fall like the previous? Does bowing direction make any difference? My bet is that they are all over the place.

Drums probably have a consistent polarity if the are mic'd above or below.

Pondering...

dcstep
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Re: Inverting polarity

Ethan said this on his site:

    "Myth: Absolute microphone or speaker polarity makes an audible difference.

    Fact: While nobody would seriously argue that it is okay to reverse the polarity of one signal in a stereo pair, I've never been able to determine that reversing the polarity of one signal - or both if stereo - ever makes an audible difference. Admittedly, it would seem that absolute polarity might make a difference in some cases, for example, when listening to a bass drum. But in practice, changing the absolute polarity has never been audible to me.

    You can test this for yourself easily enough: If your console offers a polarity-reverse switch, listen to a steadily repeating bass drum hit and then flip the switch. It is not sufficient to have a drummer go into the studio and hit the drum while you listen in the control room, because every drum hit is slightly different. The only truly scientific way to compare absolute polarity is to audition a looped recording or drum sample, to guarantee that every hit is identical.

    Important Update: Mike Rivers from Recording magazine sent me a test Wave file that shows absolute polarity can be audible in some circumstances. The polarity.wav file (87k) is a 20 Hz sawtooth waveform that reverses polarity in the middle. Although you can indeed hear a slight increase in the low end fullness after the transition point, I'm still not 100 percent certain what this proves. I suspect what's really being shown is a nonlinearity in the playback speaker, because with a 50 Hz sawtooth waveform there is no change in timbre. However, as Mike explained to me, it really doesn't matter why the tone changes, just that it does. And I cannot disagree with that.

    More Update Info: After discussing this further with Mike in the rec.audio.pro newsgroup I created two test files you can download and audition yourself. The Kick Drum Wave file (324 KB) contains a kick drum pattern twice, with the second reversed. Play it in SoundForge or any audio editor that has a Loop mode, so you can play it continually to see if you hear a difference. The Voice Wave file (301 KB) is the same but with me speaking, because Mike says reversing polarity on a voice is surely audible. I don't hear any difference at all. However, I have very good loudspeakers in a room with proper acoustic treatment. As explained above, if your loudspeakers can't handle low frequencies properly that could account for any difference you might hear. "

Sounds to me like Ethan's set in his answer. So, if I play the Sheffield "Drum Record" and I hear a difference when I switch polarity, then it's because my speaker set up is crap and Ethan's is not.

I call BS. He kind of hints that he may actually hear something in the recording sent to him, but dismisses it as unimportant. I'm not going to go through my collection and mark "+" or "-" on every LP, CD or SACD, but it's worth using a test CD to set it up for a known and just leave it there.

If you can't hear a difference, then forget about it.

Dave

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Re: Inverting polarity

"I'm not going to go through my collection and mark "+" or "-" on every LP, CD or SACD, but it's worth using a test CD to set it up for a known and just leave it there."

Ah, but therein lies the rub.

There are three "polarity" states that come into play ("+", "-", and varying degrees of "+/-") and a "set it and forget it" policy ignores a significant number of pieces that you may well prefer with "proper" polarity setting.

I look at it as though there are recordings that stay "true," but by the time they make it to our systems, we do not know until we listen which polarity is in place, and probably many recording with a "mix" of polarities - that may sound better with one setting or another.

Some albums can even have this change from track to track!

Some discs I know from repeat listening which setting sounds best for me and I set it in advance, others I just flip the switch on the fly, and sometimes I just don't care.

I'd vote to keep this all in mind for when you aren't digging a disc and then seeing if this intervention makes a difference.

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Re: Inverting polarity


Quote:

I'd vote to keep this all in mind for when you aren't digging a disc and then seeing if this intervention makes a difference.

I agree with this 100%. If in doubt or concerned about a source, I'll flip the polarity just to see if it gets better.

Dave

Elk
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Re: Inverting polarity

Great idea. I have not tried this in this context. I need to.

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Re: Inverting polarity


Quote:
What happens with 'cello? If you play a series of quarter notes, for example, does each note either start with a rise or fall like the previous? Does bowing direction make any difference?


I'm pretty sure bow direction doesn't matter. Bowing works via process called "stick-slip," where the bow alternately sticks to the string, then slips suddenly. This creates a sawtooth wave, which is then shaped by the instrument's body resonances. See this:

http://www.phys.unsw.edu.au/jw/Bows.html

The graphic on that page shows a pulse wave, but I think it's really more like a sawtooth. The only way to verify is with an electric violin or cello, which I don't have here. All of the wave files I have are real instruments, and once the body resonances are present those dominate the wave form.

--Ethan

ethanwiner
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Re: Inverting polarity


Quote:
if I play the Sheffield "Drum Record" and I hear a difference when I switch polarity, then it's because my speaker set up is crap and Ethan's is not.


Where did I say that Dave?

All loudspeakers are nonlinear, including mine.

--Ethan

Elk
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Re: Inverting polarity

Cool link, Ethan. Thanks!

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Without understanding how the

Without understanding how the organ of Corti works, that the conversion of sound into nerve signals has a (chemical) rectictifier effect, one can do many experiments but get no satisfactory explanation.

I have used a TacT Millennium with bridge mode output to speakers, Audiostatic open baffle electrostatic fullrange loudspeakers (no passive woofers) to get the amp-speaker part of the chain strictly symmetric. It is possible to repeat all tests with the speakers turned 180° in the room.

Test samples were inverted on the hard disc by using SoX software. Pos and Neg samples were played via Millenniums internal remote polarity selector.

The reversed polarity has the same effect as always, no matter what material was used. One can use mono signals from a single speaker, mono signal from both speakers (one mp output driving them in parallel) or stereo.

A remote control helps to learn the many aspects of correct vs inverted polarity music material. It is easier with XY /MS recordings than with wide spaced omnis.

Ethan may be right with his observations about speakers nonlinearity but his conclusion may be misleading. The reversal of polarity can be heard from symmetric and non symmetric speakers.

Will a non-symmetric behavior of the speaker in cabinet laid over the signal make it more difficult or easy to detect a difference?

The inner ear non symmetric behavior of the cilia and related chemical transmission is the key for understanding the discussed polarity effect. Simplified: Only the positive transistions are converted into firing a nerve signal. If a pulse starts with a negative slope, there are several overtones before the first fundamental positive transient happens. This explains the variation of timbre perception.and unfortunately lateral localization of treble varies from bass if levels are equivalent.

Best regards Martin

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