Absolute Polarity

Topics regarding professional record cutting.

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markrob
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Absolute Polarity

Post: # 14488Unread post markrob
Fri Apr 22, 2011 11:17 am

Hi All,

Does anybody know if there is a standard for absolute polarity with regard to cutting? For example, should the head stylus move towards the center of the disk when a positive pressure from the playback speaker is desired? I'd be surprised if there wasn't given all the audiophile interest in this.



Mark

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gold
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Post: # 14497Unread post gold
Fri Apr 22, 2011 5:10 pm

Yes there is. There is a JAES paper on it but I haven't been able to figure out the document number. I'm working on sussing it out.

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jjgolden
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Post: # 14498Unread post jjgolden
Fri Apr 22, 2011 5:42 pm

Here's some general info I found:
http://www.aes.org/tmpFiles/aessc/20110422/aes14-1992-r2009-i.pdf

This whole topic get's grey & fuzzy though when people mix older pin3 hot with newer/other pin 2 hot gear during recording/mixing/mastering.

Not sure about initial stylus excursion direction. Have to run a positive polarity "blip" through the lathe chain then check the microscope scope after the cut to see it's initial direction to see if it's towards or away from disc center...

Flo should know...

I'm Curious now too...

JJG

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gold
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Post: # 14499Unread post gold
Fri Apr 22, 2011 5:55 pm

jjgolden wrote:Here's some general info I found:
Have to run a positive polarity "blip" through the lathe chain then check the microscope scope after the cut to see it's initial direction to see if it's towards or away from disc center...
And don't forget the microscope on the lathe reverses the image. That could be a big oops.

There is an AES paper that I know of that talks about absolute polarity in electromechanical systems. ABG is on the case. I asked him the same question a little while ago.

The easy way to test it would be with a diode clipped sine wave. That way you could just look for the flat top under the microscope.

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Post: # 14502Unread post jjgolden
Fri Apr 22, 2011 6:37 pm

I believe most VMS-70's are Pin 3 hot as well...

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gold
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Post: # 14503Unread post gold
Fri Apr 22, 2011 7:10 pm

The Neumann disk cutting equipment uses 5 pin XLR's for audio connections. 1=G, 2=L+, 3=L-, 4=R+, 5=R-

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Post: # 14504Unread post jjgolden
Fri Apr 22, 2011 7:34 pm

Thanks Paul your right.
That would be another area to check for correct polarity.
The wiring from the 3pin XLR to the 5 pin connector.

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Post: # 14516Unread post dubcutter89
Sat Apr 23, 2011 8:11 am

There is a virtually standard by georg neumann which says that:
"positive half-wave of a lateral recording has to move to edge of the record"

knowing the relation between mono and stereo you can now define every polarity in your system.
might be important for correct working of your vari-pitch.

Lukas
Wanted: ANYTHING ORTOFON related to cutting...thx

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markrob
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Post: # 14519Unread post markrob
Sat Apr 23, 2011 10:21 am

dubcutter89 wrote:There is a virtually standard by georg neumann which says that:
"positive half-wave of a lateral recording has to move to edge of the record"

knowing the relation between mono and stereo you can now define every polarity in your system.
might be important for correct working of your vari-pitch.

Lukas
Hi Lukas,

Thanks for the info. I was interested in this as there was a question about polarity in another recent thread. I replied that there was not. However after thinking about it some, I realised that if one cares about absolute polarity, there is indeed a correct polarity. Given all of the possible places in the signal chain for a reversal to occur, I wonder how often it is correct on recordings.

Mark

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Re: Absolute Polarity

Post: # 49096Unread post jesusfwrl
Wed Jan 24, 2018 3:31 pm

There are quite a lot of standards covering absolute polarity, although most of them do not explicitly call it "Absolute Polarity". The only one that is actively maintained and does explicitly cover the topic of absolute polarity, is the AES26-2001 (r2011).

I have just written an article on this subject for my new blog, which you can read here:
https://agnewanalog.blogspot.com/2018/01/absolute-polarity-for-disk-records.html

It contains a list of standards, it mentions a suitable test record for verifying the polarity of your reproduction system, along with some remarks on the correct use of the record, as well as some practical points to consider when setting up a disk cutting system.
~~~ Precision Mechanical Engineering, Analog Disk Mastering ~~~
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Re: Absolute Polarity

Post: # 49552Unread post boogievan
Mon Mar 05, 2018 3:30 am

Forget about looking at which direction the stylus swung. The easy way to calibrate your cutting system is to have polarity flip switches for both channels of gramophone playback on your console and to listen to several records to confirm that you can hear the Wood Effect (one deflection makes the bass slightly fuller sounding and the treble very slightly higher pitched (such as the pitch of the high hat), and the other deflection subtly softens the bass impact and slightly lowers the pitch of treble instruments (again, the hi hat is an easy indicator)). Verify which deflection of those switches is standard. Once you know which way the flip switches should be set, cut some tunes and see if they sound acoustically correct with the switches in the normal or inverted positions. If they sound correct with the switches in the inverted position, adjust the absolute polarity of the .wav file (or use absolute-polarity-switching connectors on the outputs of your tape machine) and cut again and check to verify.

This matters because we can discriminate between an atmospheric compression and a rarefaction. The leading edge of the atmospheric pressure wavefront takes precedence in the auditory mind, and an initial compression of atmospheric molecules makes more volts in our brains than does an initial rarefaction (for obvious reasons)! Asymmetrical waveforms are what we're listening to with most musical instruments and voices, so, it totally matters... ... unless you listen to music on most loudspeakers! (Read further for why...)

Alas, most multi-driver loudspeakers have phase-tangling cross-overs. For me, only single-driver transducers (such as most headphones) or multi-driver loudspeakers that use 1st-order crossovers (where the roll-off introduced for each driver is only 6 dB per octave) have the ability to present the sound image without enough group delay to mask the Wood Effect.


If you want a short cut to finding the right way to deflect your polarity flip switches, you can buy a copy of Miles Davis Sketches of Spain by Columbia. They cut that in incorrect acoustic polarity, which means that the muted trumpet sounds a little sour. When you flip the red and black wires going into your loudspeakers to the non-standard positions (or flip both polarity flip switches on your console to the non-standard deflection) the muted trumpet will jump out at you.



- Boogie

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Re: Absolute Polarity

Post: # 49557Unread post jesusfwrl
Mon Mar 05, 2018 7:41 am

Boogie, as you correctly point out, many loudspeakers may not be phase-coherent enough to allow accurate determination of absolute polarity by ear. Further, many recordings were done in ways which also smear the time information we would need to perceive absolute polarity inversions. In my view, it is a lot faster and more accurate to verify each piece of equipment in the studio once only, during installation/commissioning, using test signals or test media, as appropriate, and a scope, to know for sure that everything is maintaining absolute polarity by default throughout the chain. The switches are really useful, but I like having an accurately calibrated system and not have to guess.

Unless I detect problems, or a customer specifically asks for changes in the sound or a polarity inversion, I will maintain absolute polarity from source to lacquer by default, even if the recording does not sound much different inverted. When a few thousand copies of the record reach the market, there's always a chance that someone out there will have accurate speakers and good ears, and it is after all our duty to provide them with the most accurate possible auditory experience, in accordance with the intentions of the producer.
If I feel that something sounds better if I invert it, I will call the producer and ask for permission to do so. I always do test cuts anyway and I always send a digitized test cut as the bare minimum, if not a reference lacquer disk by post, if not an attended session, for the approval of the producer prior to proceeding with cutting the actual masters. I may do an inverted and a non-inverted test cut and let the producer decide. I once even sent A/B/X files, that was fun!

"Sketches of Spain" is indeed an interesting album to experiment with polarity inversions. Muted trumpets are known to make polarity inversions quite obvious.
~~~ Precision Mechanical Engineering, Analog Disk Mastering ~~~
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Re: Absolute Polarity

Post: # 49798Unread post Max
Tue Mar 20, 2018 3:21 pm

Hello all.
IEC 60098 (1987) Paragraph 11.4.4 recommends:
'Channel Polarity:
Stereophonic reproducing equipment should preferably be so connected that movement of the reproducing stylus tip along the radial line through stylus tip and disk centre in a direction away from the disk centre shall produce compression in front of the left and right-hand loudspeakers similar to that produced by the live programme source.'

There is concrete definition within JIS C5503 (1979) but I don't have this at hand. Perhaps our colleagues from Japan can help. Basically it defines that when the stylus is displaced toward the outer radius of the disk, the pickup should generate a positive [+] voltage.

Both standards apperently coincide here.

Daniel/SST

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Re: Absolute Polarity

Post: # 49925Unread post boogievan
Thu Mar 29, 2018 7:11 am

Left_High_In.jpg
- from PHYSICAL PROCESSES OF CUTTING GRAMOPHONE RECORDS by Fritz Nygaard

For one-channel-at-a-time stereo cutting - the left channel diagonal motion for the positive 'swing' half-cycle of a/c program causes the stylus tip to move up and away from the spindle - while the right channel diagonal motion for the positive 'swing' half-cycle of a/c program causes the stylus tip to move down and away from the spindle.

When the stereo cutting head shown is cutting a mono program - and, therefore, has applied to each drive coil the same signal (in intensity and phase) - the positive 'swing' half-cycle of mono a/c program causes the stylus tip to move, laterally, away from the spindle.

- Boogie
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Re: Absolute Polarity

Post: # 49943Unread post jesusfwrl
Sat Mar 31, 2018 8:42 am

Daniel, all standards are in agreement regarding polarity, fortunately. Having said that, standards need to be updated or at last reaffirmed at intervals not exceeding ten years, in order to remain valid.

As such, I find it inexcusable that organisations such as the IEC, JSA, DIN, and BSI allow themselves to fall so low as to keep on offering for sale what is effectively long expired documents, compiled over 31 years ago at best, without even bothering to at least review and reaffirm them as currently valid industry documents. I consider this an essential responsibility which shall burden any serious standards institute, if they are to retain their respectable status.

Then we have examples such as the SMPTE and the EBU, who do not even consider the disk record as a medium worthy of standardisation and inclusion in their latest polarity standards, which are both now outdated without any revision in 20 years.

Fortunately, the AES is the only organisation offering a proper valid polarity standard, dating back to 2011. This should be revised/reaffirmed by 2021 if it is to remain valid. It is the only multi-medium polarity standard which includes disk records.

I would support and participate in any attempt to revise any of the general disk-specific standards, or to compile a new one, to be handled by an organisation with an active interest in the preservation of the disk medium and a commitment to keeping standards documents actively maintained, valid and relevant. This would surely increase their acceptance and adoption by the industry, which is the ultimate measure of success for any standard.

Boogie, although the "Physical Process of Cutting Gramophone Records" is by no means a standards document in itself, what it correctly describes in Figure 5.1 is a reflection of what was described in the relevant standards at the time, which remains unchanged to date. Very informative book in general, I would highly recommend it to anyone who has not read it yet.
~~~ Precision Mechanical Engineering, Analog Disk Mastering ~~~
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chris-zwarg
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Re: Absolute Polarity

Post: # 50343Unread post chris-zwarg
Wed May 16, 2018 6:01 pm

The consistent standard of "positive pressure = stylus moving to record edge" goes back to the ancient mechanical recording and playback method: All mechanical recording lathes and gramophones cannot but work this way due to the simple horn+diaphragm+lever+stylus assembly. Any gramophone soundbox (to look first at the, more familiar, playback side of things) connects the left side of the diaphragm (facing the disc center) via the hollow tonearm to the horn. When the levered stylus moves outward, it pushes the diaphragm inward, and the latter forces air out of the horn. When the stylus swings inward, it pulls the diaphragm outward and air is sucked into the horn. RECORDING soundboxes always had the horn attached to their _right_ side, for purely practical reasons, namely to have no tubing or horn hanging over the wax blank, where they would have been in the way when changing blanks, removing the swarf and visually controlling the cut. Sound pressure going into the recording horn from the right (edge) side necessarily forces the diaphragm out of the soundbox' pressure chamber, towards the center of the disc, while the stylus at the lower end of the connecting lever moves in the opposite direction, i.e. towards the edge of the disc. Rarefication of the air in the recording horn sucks the diaphragm into the soundbox (direction edge-of-disc), and the stylus at the other end of the connecting lever moves centerward. No possibilities for phase shifts at any point - likely one important reason why a well-adjusted mechanical gramophone playing a well-preserved mechanically-recorded disc is capable of a surprisingly lifelike reproduction of mid-range sounds like tenor and baritone voices, trumpets, clarinets, xylophone, all that stuff that made up the earliest record catalogues (and indirectly, it provides and explanation why electronically enhanced "modernizations" of such early recordings often lack the same lively impact, namely through the enormous phase-shift and impulse smear caused by complex post-processing with its usual combination of parametric, notch, and bandpass filters to compensate acoustical resonances and improve signal-to-noise ratio).

For two decades following the introduction of electric recording in 1925, consumer-market discs would still mostly be reproduced mechanically, so the old standard that produced correct polarity with mechanical playback was simply kept for maximum compatibility. No need to "update" or confirm it every ten years (as someone here suggested), when the basic principle behind the recording process worked like this from Berliner's very first experiments in the 1880s, without having even to think about a "standard", simply because the physical layout of the machine would be less practical and economical in mirror-image: On the recording side, tubing or recording horns laid across the blank disc would definitely hinder the recordist, who needs to work on the turntable side of the thing while the artists need to face the open end of the horn - in front of the engineer with the common setup, but in his back with the theoretical "left-handed" approach; while a gramophone (playback) soundbox with the arm attached to its right (away from the disc center) would require extra space beyond the turntable edge on that side of the machine - especially unpractical for the (ubiquitous) portables and closed-lid models.

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Re: Absolute Polarity

Post: # 50411Unread post jesusfwrl
Tue May 22, 2018 7:43 am

chris-zwarg wrote:The consistent standard of "positive pressure = stylus moving to record edge" goes back to the ancient mechanical recording and playback method: All mechanical recording lathes and gramophones cannot but work this way due to the simple horn+diaphragm+lever+stylus assembly. Any gramophone soundbox (to look first at the, more familiar, playback side of things) connects the left side of the diaphragm (facing the disc center) via the hollow tonearm to the horn. When the levered stylus moves outward, it pushes the diaphragm inward, and the latter forces air out of the horn. When the stylus swings inward, it pulls the diaphragm outward and air is sucked into the horn. RECORDING soundboxes always had the horn attached to their _right_ side, for purely practical reasons, namely to have no tubing or horn hanging over the wax blank, where they would have been in the way when changing blanks, removing the swarf and visually controlling the cut. Sound pressure going into the recording horn from the right (edge) side necessarily forces the diaphragm out of the soundbox' pressure chamber, towards the center of the disc, while the stylus at the lower end of the connecting lever moves in the opposite direction, i.e. towards the edge of the disc. Rarefication of the air in the recording horn sucks the diaphragm into the soundbox (direction edge-of-disc), and the stylus at the other end of the connecting lever moves centerward. No possibilities for phase shifts at any point - likely one important reason why a well-adjusted mechanical gramophone playing a well-preserved mechanically-recorded disc is capable of a surprisingly lifelike reproduction of mid-range sounds like tenor and baritone voices, trumpets, clarinets, xylophone, all that stuff that made up the earliest record catalogues (and indirectly, it provides and explanation why electronically enhanced "modernizations" of such early recordings often lack the same lively impact, namely through the enormous phase-shift and impulse smear caused by complex post-processing with its usual combination of parametric, notch, and bandpass filters to compensate acoustical resonances and improve signal-to-noise ratio).

For two decades following the introduction of electric recording in 1925, consumer-market discs would still mostly be reproduced mechanically, so the old standard that produced correct polarity with mechanical playback was simply kept for maximum compatibility. No need to "update" or confirm it every ten years (as someone here suggested), when the basic principle behind the recording process worked like this from Berliner's very first experiments in the 1880s, without having even to think about a "standard", simply because the physical layout of the machine would be less practical and economical in mirror-image: On the recording side, tubing or recording horns laid across the blank disc would definitely hinder the recordist, who needs to work on the turntable side of the thing while the artists need to face the open end of the horn - in front of the engineer with the common setup, but in his back with the theoretical "left-handed" approach; while a gramophone (playback) soundbox with the arm attached to its right (away from the disc center) would require extra space beyond the turntable edge on that side of the machine - especially unpractical for the (ubiquitous) portables and closed-lid models.
Chris, thank you for your account of the acoustic side of things. I do have a very early Garrard gramophone, which I restored almost ten years ago. A truly amazing piece of engineering. This machine, along with a number of other reproducing and recording equipment of the acoustic era, work as you have described.

However, I shall point you to the "Manual of Analogue Sound Restoration Techniques" by Peter Copeland, pp 249-278, as well as "The Victor Talking Machine Co. new process of recording", by George Brock-Nannestad, published in the "Historic Record" No. 35, April 1995. They describe the arrangements of multiple horns, coupled to both sides of the soundbox diaphragm, as well as a dual-diaphragm arrangement.
I also remember reading about dual-lever soundboxes, which would invert the polarity, but I do not have a reference at hand.

In such cases, it is very likely that acoustic recordings of opposite polarity would result. Peter Copeland does state though, on page 22 of his book, that most acoustic recordings will most probably adhere to the polarity standard.

My statement regarding the need of reaffirmation of standards documents every ten years has more to do with how the world works rather than with how records work. It is highly unlikely that what has come to be standardised as polarity of disk records will ever change. What will change and does change over time is the status of standards organisations in different parts of the world and the acceptance of their documents by the industry.

While standards pertaining to disk records are in agreement regarding polarity, there are many other aspects of record manufacturing where the standards deviate from each other. Considering that they are well out of date, and even when newly published, some were regional, the standardization situation in our industry is, to put it politely, rather vague. Commercial practices and requirements have changed within the past 20 years. While the AES standard mentioned in my article (freely available at https://agnewanalog.com/blog/2018/04/11/absolute-polarity-for-disk-records/) is up to date, it only covers polarity for different media.

I believe our industry would benefit from a single, revised, well-planed, carefully written, comprehensive standards document, representing all interested parties, which would be universally accepted, and maintained as appropriate, at least once every 10 years, so it can keep on representing all interested parties and remain universally accepted, respected and implemented by record and associated recording and reproducing equipment manufacturers.
~~~ Precision Mechanical Engineering, Analog Disk Mastering ~~~
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Re: Absolute Polarity

Post: # 50834Unread post boogievan
Wed Jul 18, 2018 3:33 am

Yes, Nygaard got it right, citing in his 1979 paper having used texts borrowed from 'Danmarks Tekniske Højskole'. Also, fwiw, Section 5 of the paper containing the image I attached is listed in the table of contents as 'Standards'.

(For the record, the image is a screen grab from the .pdf available at torbenteknik.dk. The text in my last post was my own description of what the image depicts.)

Some have called for a new standard to be published, but Lavry Engineering has the right idea - assume that the acoustic polarity of the playback of some recordings is inverted, due to a probably-inadvertent absolute polarity reversal at some stage of recording that wasn't corrected, for whatever reason(s), during mastering, or in the playback chain, itself. Since this is a correct assumption, and we can't probably just wave a hollywood wand over each record before we play it and expect magick to heal the presence of a potential inversion (unless we have played it before on the same system and know that the system hasn't been disturbed and therefore already know that the record is going to signal to our gear correctly [... but that would only be 'magic', without the 'k', as in a 'parlour trick' (;]), let the audiophile simply place a polarity inverting switch for each channel on his playback console. Then, if s/he can hear a difference, s/he can select the preferable polarity and thereby best enjoy all existing pressings, injection-moldings, and .wav files. Recuts of Miles Davis or Chopin are not needed. Better monitoring with the Wood Effect switch is needed!

It might have been helpful to ensure that the balance engineers were monitoring correctly when they decided how to adjust faders and eq knobs. But we have no way of knowing from the recording, itself, if they heard it correctly. Maybe they were using conventional loudspeakers with high-order cross-overs that mangle impulse response and therefore couldn't have heard the Wood Effect in either switch position if they even had it. The risk of hearing a good recording in less than the best sonic light persists, standards or no... Whereas the switch that Lavry puts on each of their 'gears' solves the worst part of the problem and should be an ensample to all.


servus,
Boogie

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Re: Absolute Polarity

Post: # 50838Unread post Dub Bull
Thu Jul 19, 2018 6:40 am

I like how the Analog blog cites the AES Polarity Standard (26), revision to AES-26-1995, and later, including absolute polarity of 'Mechanical disc records' and the standard's recent 'Stabilization' in 2017. AES Members can download it, free. Otherwise, it's pretty expensive. The standard is current and its practice is general. So, making your records look and sound like the majority in your collection of pressings works, too (and precludes overlooking some part of the total chain of QC chez vous).

While there are a number of pressings that would signal with inverted acoustic polarity with a conventionally-wired set-up, some would possibly be healed on 'unknowingly mis-wired' systems. Also, most will not bother implementing a Wood Effect switch since it requires a little effort and not doing it has worked fine for years.

Acoustic polarity is what Wood demonstrated to be audibly discernable. It doesn't care what pin went high until it is heard.

I have an _____ (big, 'late' R&B star chanteuse) compilation CD (commercially molded and bar-coded, shrink-wrapped replicate) that makes unnatural acoustic polarity on many tracks (if one has a standards-conforming, non-inverting system), but not on all (tracks). I used to wonder if the ME was deliberately inverting it to soften the surfaces, since it kind of makes it a little bit blurry or smooth but in a micro-dulled sounding way, by comparison to the natural arrival of the wavefront when I flip the stereo polarity switch (in real time). I've liked the sound of recordings that I only (much) later realized would sound a tiny bit better if I switched the wires for each channel from hi to low and low to high on playback. I don't anticipate a trend towards this. It's more like an Easter egg for audiophiles. Enough preaching to a choir... (;

[He] is risen,

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Re: Absolute Polarity

Post: # 50839Unread post jesusfwrl
Thu Jul 19, 2018 7:37 am

boogievan wrote:Yes, Nygaard got it right, citing in his 1979 paper having used texts borrowed from 'Danmarks Tekniske Højskole'. Also, fwiw, Section 5 of the paper containing the image I attached is listed in the table of contents as 'Standards'.

(For the record, the image is a screen grab from the .pdf available at torbenteknik.dk. The text in my last post was my own description of what the image depicts.)

Some have called for a new standard to be published, but Lavry Engineering has the right idea - assume that the acoustic polarity of the playback of some recordings is inverted, due to a probably-inadvertent absolute polarity reversal at some stage of recording that wasn't corrected, for whatever reason(s), during mastering, or in the playback chain, itself. Since this is a correct assumption, and we can't probably just wave a hollywood wand over each record before we play it and expect magick to heal the presence of a potential inversion (unless we have played it before on the same system and know that the system hasn't been disturbed and therefore already know that the record is going to signal to our gear correctly [... but that would only be 'magic', without the 'k', as in a 'parlour trick' (;]), let the audiophile simply place a polarity inverting switch for each channel on his playback console. Then, if s/he can hear a difference, s/he can select the preferable polarity and thereby best enjoy all existing pressings, injection-moldings, and .wav files. Recuts of Miles Davis or Chopin are not needed. Better monitoring with the Wood Effect switch is needed!

It might have been helpful to ensure that the balance engineers were monitoring correctly when they decided how to adjust faders and eq knobs. But we have no way of knowing from the recording, itself, if they heard it correctly. Maybe they were using conventional loudspeakers with high-order cross-overs that mangle impulse response and therefore couldn't have heard the Wood Effect in either switch position if they even had it. The risk of hearing a good recording in less than the best sonic light persists, standards or no... Whereas the switch that Lavry puts on each of their 'gears' solves the worst part of the problem and should be an ensample to all.


servus,
Boogie
A technical or industrial standard is not meant to prevent consumers from using the relevant technology in wrong ways. Nor is it meant to educate professionals on correct operating procedures.

It is simply meant to make life easier in that if universally followed, anyone following the instruction manual for their home hi-fi gear would end up listening in correct polarity. If they wire the speakers wrong, their problem.

Likewise in the professional end. It is not difficult to maintain absolute polarity throughout the recording production and manufacturing process. If people choose not to, their problem.

A switch can introduce an element of preference. Personal preferences are entirely outside the scope of standard documents.

Polarity inversion switches are also frequently encountered on multiple channel mixing desks, to help counter phase issues when using multiple microphones under time pressure. This is not necessarily the way to go for high fidelity recordings. Neither the polarity switch as a quick fix, nor the time pressure. I will openly admit I also have used it under time pressure, but it is far from the ideal way to do things. But if this is what the client wants from me, their problem. My job is to know what is ideal and advise accordingly, for those who do want to do things properly. Not everybody does and I respect their wishes and views.

An up to date standardisation is always a good thing for an industry and it does make life much easier if universally implemented. Polarity is just one of the several aspects.

What if some fan of hardcore punk music start manufacturing turntables spinning at 38 rpm and 49 rpms, because his personal preference is that everything sounds better when played faster?
Then I could cut master sat 30 rpm and not tell anyone about it, just a matter of preference. After all, who can really know if absolute speed has been maintained anyway? Isn't that why Technics added these sliders on the side? Just set the speed to taste...
~~~ Precision Mechanical Engineering, Analog Disk Mastering ~~~
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