|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
173.197.216.218
In Reply to: RE: Absolute phase/polarity posted by Bill Way on July 31, 2013 at 15:26:49
Charles Wood in 1962 developed a test to see if absolute phase is audible.
He clipped the top of the waveform and after a listening session he inverted it 180 degrees and listened again.
Results were a noticeable change in timber between the two sessions.
Here is a good article about it.
Follow Ups:
This something that I found a long time ago from Clark:
Clarkjohnsen acoustic polarity
What to listen for:
1) Better dynamics - "leading edge" of notes more defined. This is both when music is played soft or loud. But it also helps separate out softer sounds when other instruments are being played loud. This not a huge night and day thinng but is readily observable.
2) Better sound stage proportions - wider, deeper, and more forward.
3) Better focus of individual images - particularly singers, will come forward and be more separate from the "mix" when AP is right. When AP is wrong the soundstage becomes more two-dimensional and singers move back in amongst the other instruments.
4) Sibilance and distortion of higher frequencies. More sibilance on voices is usually sure test (for that microphone). Splashing and edgy cymbals another for incorrect AP. Violins are a good test - they become steely, edgy, and annoying whem AP wrong, and more silky, balanced and dynamic when AP right.
5) Bass is more dynamic, punchy, and detailed when AP correct, looser with a bloom when wrong.
6) The is more of what can best be describe as a "haze", a light fog making it harder to differentiate what is going on when AP wrong.
7) Another good test is sitting off centre - when AP is correct you will find image from the centre and far speaker "stay put" somewhat better. With wrong AP the images will tend to follow the listener more.
8) Having well designed coherent speakers with good impulse response makes it easier to differentiate all of the above - but is not essential.
Regards,
Todd
I am familiar with Clark Johnsen's work, but I have not read Wood's original study. One thing that concerns me with Wood's results is that second harmonic distortion in the playback chain (e.g. speaker) could invalidate a conclusion that human ears can hear polarity reversals, as the amplitude spectrum would differ for the two polarities of Wood's asymmetrically clipped waveform. Perhaps Wood controlled for the possibility of speaker distortion, but if so, I've not seen this discussed.
In addition to the ability to hear the effects of polarity reversal, there is the question of whether recordings sound better (e.g. more natural) when presented with correct polarity vs. reversed. There are some logical issues here, especially given that some musical instruments radiate to the audience with differing polarity according to their orientation. It would also be interesting to see if (a) one individual is consistent in his selection of preferred polarity of a particular recording and (b) multiple individuals agree as to the correct polarity when listening to the same recording on the same system. There are test devices that are designed to aid in setting up correct polarity of public address systems and these can be adapted as an tool for recording polarity experiments.
From a practical point of view, I have a polarity reversal button in my DAC and can swap it whenever I want. Along with the volume control and the location of my listening chair I use polarity to fine tune a playback so that it sounds "the way I like it", for whatever that's worth. Your mileage may vary. :-)
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
The original Wood experiment of 1957 used headphones... on cats' ears! It was cited in a 1962 article by Craig and Jeffress writing in JASA, who replicated the results on humans but without a truncated waveform.
P.A.
Using headphones could be open to the same criticism of second harmonic distortion.One test that would be immune to this kind of criticism would be if a bipolar speaker were used and it were constructed with complete symmetry and located symmetrically in the listening room. (I don't know if any commercial bipolar speakers meet this test, as the ones that I am familiar with have a clear "front" and "back".) With such a speaker one could reverse polarity by a 180 degree rotation of the speaker.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Edits: 08/03/13
Question, In a typical rock recording with maybe 15 to 25 microphones or more with all instruments having there own mike and overdubs done at different studios what does correct absolute phase really mean. Reversing absolute phase may make a recording sound different but I doubt it has anything to do with correct absolute polarity of the recording
Alan
The situation is complex if there is a forest of microphones, but if they are far enough apart and close enough to the individual instruments then the multiple microphones won't affect the polarity, assuming that the microphones, preamplifiers, and cabling is different. (There are two standards for pin-out on balanced XLR cabling, which can lead to confusion if different brands, e.g. different nationalities, are used.) In addition, figure 8 microphones are sometimes used and they are velocity sensitive, which means that the polarity on one side of the microphone is reversed. Some recordings have one microphone shared by two singers and if this is done with a figure 8 microphone the singers will be in opposite polarity.
Absolute polarity is most easily heard on a single microphone monaural recording played back on a single driver speaker system. Here all one needs is an AM table radio. Many multi-way speaker systems have their drivers wired in opposite polarity and they scramble phase, making it more difficult to hear the effect. As far as I know, none of the people who have done research on absolute polarity have done "live" vs. "recorded" demonstrations or showed that the correct polarity sounds better (rather than merely different as you suggested).
I have attended a jazz concert where the polarity of the PA system used on the singer was wrong. At the set break I went up to one of the band members and remarked that the polarity was wrong. He believed me, because he was getting bad sound and didn't know why. We reversed the wiring on both speakers and the second set sounded much better. There is test equipment that can be used to calibrate correct acoustic polarity. Getting acoustic polarity correct is essential in PA sound reinforcement situations.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
n
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: