[Myren]

Does anyone have software for sound card polarity testing?


I've got a 4 channel analog out based SB Live! (i know, i know, probably get a Revolution soon or something that doesnt suck for my Hafler DH500's), and so far i've just been using a winamp plugin that inverts the left channel. Although this is somewhat useful, I'd really like to play with four channels polarity's independently, make sure front and back polarities match up together to sound just right, in addition to just L/R polarity matching.


Thanks

Myren

 

[thomaspf]

This is an interesting thought.


So far I was under impression that you want to have the correct phase of the recording passed through all the way to the speakers. Polarity switches were invented to compensate for recording or components that have polarity inverted.


Some people claim (I have reason to not believe them) they can actually hear the effect of inverted polarity. In any case I can't imagine a scenario in which you would want to treat left and right channel different.


I would try to adjust the delay to compensate for different distances.


Cheers


Thomas

 

[Myren]

The polarity inversion is quite noticable at lower frequencies: directly out of phase bass virtually cancels itself out. Try fliping one of the wires on your speaker or amp. Its actually kind of interesting.


By simply flipping one of the signals on the computer, its possible to compensate for any such inversions in polarity in the system.


The problem is a lot of stereo to RCA jacks either dont properly set polarity, or something in the computer does not adjust polarity properly. This is further compounded by using two such connectors, front and back.


So far, i have to keep flipping wires. Get the front working, get te back working, then get front back coordinated. Its at least four wire pair flippings minimum per setup.


My SB live doesnt have distance compensation. Also, full on phase alignment is a whole heck of a lot more computationally exepnsive than simply inverting a signed signal.

 

[thomaspf]

I was trying to inject a slightly different viewpoint in your thinking.


The polarity of the signal is absolute and nothing that is to be adjusted for dealing with cancellations of your speakers. When a sound wave hits a microphone this is experienced as variation in pressure. If you want to recreate this signal correctly you need to get high pressure at exactly the same point it was recorded not low pressure which would happen as part of polarity inversion.


I don't claim I can spot these but some people can. I read some time ago that the attack and decay of strings or drums are good candidates to spot this problems. Here is one of many links you can find on the topic

http://www.siber-sonic.com/broadcast/polarity.html


The interference of the sound waves coming from a stereo pair of speakers is a different issue. Flipping connectors on your speakers or within connecting cables is not a thing I would encourage people to do. I still have to come across an RCA cable that crosses ground and signal. There are AES guidelines for the use on XLR cables to prevent polarity inversion in the recording and playback chain.

http://www.aes.org/standards/b_pub/aes14-1992.pdf



Cheers


Thomas

 

[Myren]

someplace along the way, something is crossed somewhere, cause i have to flip something to keep my sound from being inverted.

 

[Eiffel]

Issues with matching polarities are fairly easy to identify (absolute polarity is much harder to test, and may actually vary with frequency on some speakers...).


Test tracks are widely available (on Avia, Video Essentials, etc.) which will help make sure that all the speakers in your system are in phase. most of these tracks do not even require you to move the speakers (as they rely on your ability to distinguish between localized and diffuse sources)

 

[thomaspf]

If your speakers have phase shift you are limited in what you can do. However, I would expect that the shift does not hit 180 degress or anywhere close to the point that the movement of the cone is opposite to the polarity of the signal at any frequency.


Cheers


Thomas

 

[Bill Gaw2]

Absolute polarity became a problem when years ago Sony reversed the 2 and 3 pin XLR input configuration vs. Ampex. Then the japanese got the bright idea of alternating the absolute polarity on alternate traxcks of vinyl. This was continued by them into the digital era with CD's. Only Chessky, Telarc and a few other high end American CD makers used one absolute polarity configuratiojn on their recordings.

Yes, absolute polarity polarity can be heard by just about everyyone if they listen close enough, and after a while it is maddening as you cannot listen straight through recordings without having to change polarity. Out of absolute phase information sounds muddy or dull with flacid bass and deadened highs and loss of depth and width of the sound stage. This was fairly easy with 2 channels, but a real PIA with 5.1.

Interestingly, 5.1 makes it a little more difficult to hear absolute phase.

Noone makes a DVD-V,DVD-A or SACD player that will correct for absolute polarity, and when Cliff was doing the software for the REVO I hadasked him to try to include an absolute polarity switch, but it wasn't included, I think because it would have been extremely difficult for 5.1.

If you have a 1010 or other balanced card, it would be fairly easy to build a box for switching pin 2 and 3 for each channel for either balanced or unbalanceed output.

For a full description of absolute poalrity, read "The Wood Effect" by Clark Johnsen, which can be purchased from him at 617-525-7606.

Bill Gaw