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In Reply to: Speaking of Absloute Phase... posted by Ray-o-Stat on August 4, 2005 at 21:21:28:
Beyond the presence of some low bass and familiarity with the music
how do you determine whether the recording is in correct phase or not ?
This is something I should know.
Follow Ups:
Andy pretty much explained it.
All I can add beyond that is that phase coherency of a speaker system, especially crossover also plays into this. For some reason, I have alwyas been particularly sensitive to phase anomalies and have found solace in having speakers that have, no crossover, or a crossover only in the bass.When you come across recordings that either just sound spatially wrong, or the vocals seem unduly strident, drums or percussion sound like cardboard, or the stage seems constricted or even conical, these are all indications that there is likely an absolute phase problem. The records and cd's I mark as being out of absolute phase are those that I identify and also sound best when the system is switched to invert phase. There are recordings, as others point out, that are an absolute (pun intended) mess, where different instruments or mics are inverted but not all! With recordings like that, there's no hope as they do not sound right in either setting...
Ray My present loudspeakers are back Horns driven by single Fostex
166 ES-R Full range drivers, so no crossover either except when I'm using my sub.
Regards Fred
Fred,I don't think "absolute polarity" has got anything to do with the presence of low bass or not. That's more associated with relative polarity between R & L channels.
As Elmo pointed out, if the drum is recorded with correct polarity then the cone should go out with the strike. However, that doesn't give you any guarantee that all the other mikes have been connected with the same polarity!
If you have a polarity reversal switch on your preamp or phono stage then (if the track has been recorded correctly - with all mikes in the same polarity) flipping it one way should make the soundstage more defined and, particularly, a singer to sound more focussed. If the track was recorded with various mikes in opposed polarity, your simply exchanging one mess for a reversed mess!
If you haven't got a polarity reversal switch then forget about it! Jumping up to change speaker leads is too much of a PITA!! I obsessed about absolute polarity for several years and even went so far as to build a polarity reversal circuit into my phono stage. Then I found out that this circuit was actually degrading my sound ... so I removed it and I no longer worry about it!
Regards,
AndyThanks for the very informative post, for the most part most of my concerns regarding polarity were with subs where out of phase muddy's things up considerably re-enforforses distortion and seems to cancel out some of the frequencies near the crossover freq.
A drum that is close-miked from above (snare, toms) has to be reversed in polarity, to make the speakers move outwards at the point of attack. However, most engineers don't do this as it is not common knowledge. When a snare drum is miked from top and bottom, the bottom mike is reversed in polarity to avoid frequency cancellations, while in fact the bottom mike should be left alone and the top mike should be reversed.Bass drums are usually miked from the inside, where air is pushed into the microphone membrane. This mike should also be left alone, and the same goes for any drum that is miked from underneath.
This applies ONLY if the whole recording studio is wired correctly, in absolute phase.
The phase-reverse switch on some amplifiers are really great, because when you play with different settings, you will find that one setting sounds better than the other, depending on the recording.
Best regards,
an overhead drum mic does not have to be reversed, it depends but certainly the fact that it is close has nothing to do with it. It does have to do with the polrity of the mic itself, but its phase coherence with other microphones will be by far the most important issue.
Assuming that the polarity of the whole audio chain (including the mike) is correct, phase-inverting the tom and snare mikes makes a increase in definition, slight but audible. I am a drummer and I've tried this myself after producer/engineer Jay Graydon told me about it.Phase-reversal only makes sense with close-miked drums, close-miked meaning a distance of 1 to 3 inches. Drumheads move inwards when struck by a drumstick, and the resulting air-pressure makes the microphone membrane move outwards, and ultimately, the speaker cone to move inwards. Overhead mikes, which I call "distance mikes" are not as fast as the individual close mikes, and absolute phase becomes unimportant. The sound from these mikes are much more of a blend between reflected and direct sound, than the close mikes which is mostly direct sound.
Best regards,
by the way, if it were me, I wouldnt be using close mics on the toms anyway, because it creates phase problems. Since phase is all about arrival time, it really screws things up. The fewer mics you can get away with the better. That said, most engineers, technically speaker, recording everything a certain degree out of phase if they use more than one microphone. not 180 but somewhat, which is why you hear comb filtering,; a nasty sound.
And the way many engineers "deal" with these phasing problems, is by using noise gates, furhter degrading sound quality.The fullest, deepest and most natural-sounding recordings I've ever heard are still the classical "Decca tree" recordings from c. 1959-1969 on the Decca SXL label. Not all of them, but most. Three mikes (usually Neumann M50) placed in front of the orchestra in a (usually) great hall.
Multi-miking is overrated, I agree. I've found that usually, the more recorded channels, the less the chance that the levels will be set correctly at mixdown. With 140 tracks of Pro-Tools audio, people just don't pay much attention to every track any longer.
Best regards,
my point was that if you are talking about one mic, you shouldnt have to reverse the phase unless your microphones polarity is different than your microphone preamp's.
nt
at lowish to mid volume, gently place finger on woofer or mid bass unit. Cone should move out/forward during percussive notes.
Excellent advice !
hmm, I'll have to try that on my CLS's
=8^D
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