Phil Leigh;479488 Wrote: > This one keeps coming up. I've been miking up drum kits in the studio > and on stage for over 25 years. Let's look at the kick drum. Often (in > the studio) there will be two mics, one either side of the skin (one > will pickup the beater click if you want that sound). These mics need to > be out of phase with each other or they will partially cancel. Then > there's the snare. If I top-mic it, which way should the speaker move? > If I mic it above and below, again I need to reverse the phase of one of > these mics. If I end up in a situation where I have an array of mics > around a kit, some of which are facing each other, then I need to think > even harder about relative phase... or actually I don't. I simply aim > for the best sound - not one that has any phase coherency. I can't > achieve phase coherency anyway because the sounds are all bleeding into > each other so each mic will receive a complex mixture of sounds. It can > turn out that the kick drum mic will be the only one to be reversed!. > > The point is that the only time a speaker is EVER going to be asked to > produce a truly phase coherent output is if you feed it with an > artifically generated impulse response. Of course, most speakers can't > produce anything more than a vague emulation of one of those anyway... > > > I'm convinced this whole "kick drum" example came about because people > see a kick drum skin as a vertically mounted circular sound source that > is obviously driven from one side. Then they look at their speakers and > what do they see? - oh yes that's right, one or more vertically mounted > circular sound sources driven from one side... > > Well, as far as I'm concerned that's the beginning and the end of the > comparison. A 6-15 inch driver mounted in a closed or semi-closed box > will never behave like a 26 inch drum head mounted in an open tube... > > What about speakers whose drivers don't face forward? - upward? omnis? > non-pistonic drivers? pressure zone microphones? direct contact > transducers? > > Even the very best speakers in the world are not true dipoles operating > in free space (most of them don't even try to be) so one might expect > there to be some asymmetry in the sound from the front of the driver vs > the rear. > > The only signal that moves a driver in one direction only is DC... > > The bottom line is this. The recording process does not seek to > preserve absolute phase. The replay chain doesn't either. All music we > listen to contains a mixture of sounds with different relative phases > (we don't tend to record in anechoic chambers...and even if we did we'd > immediately slap phase-mangling reverb all over it!). Rememer that all > reflected sound will have it's phase altered. > > This is why I stand by my opinion that there is no right or wrong in > terms of absolute phase/polarity. > > As to the thorny question of why some people can detect 180 degree > phase changes and is it important?... detection of a difference does NOT > imply there is a right or wrong answer. Not everyone will agree on the > preferred overall polarity and they won't know which one is > theoretically "correct" anyway. > > If you have access to the Alan Parsons/Steven Court Sound Check CD you > can try it for yourself - there's a real isolated kick drum track on > there (with some bleed through clearly audible). Which polarity setting > do you prefer? > Track 73=kick drum, track 74 = snare... > > Phil
Hi Phil, >From the perspective you describe (a multi miked drum kit), I agree that phase problems will be introduced and it is likely that polarity problems will also be introduced by the multitude of mics used. Phase problems will indeed cause smearing which will make it more difficult to decide or know which polarity sounds better. If polarity is not maintained on each recorded mic in the array, the problem becomes even more complex. I believe that the less mics used, the easier it would be to determine which polarity is better. A stereo pair in a Blumlein pattern used to record a jazz session for example would not have the same phase problems (provided the polarity for the xy pair is maintained to be the same). In the case of multi-miking where phase and polarity flipping of individual tracks exist, I think the listener should handle polarity for the playback of the final mixed track as follows. They would listen to the recording at both 0 and 180 degree polarity and try to focus on what improves the most in the mix, and that of course depends on what the listener is biased to focus on. The listener may focus on the snare or the kick drum for example (this is of course material dependent because the song in question may use the snare and kick very sparingly but instead may use toms/floor/cymbals more so). If an improvement is heard at one polarity setting over the other in the situation described, then that's what the listener would choose. Introduce a full 24 tracks or more that include guitars, bass, vocals, room mics, etc... and the focus may move from drums to something like vocals. If the polarities of all tracks committed to tape are inconsistently 0 and 180, it is impossible to know what is right. For example if the kick and snare were recorded at zero polarity and the vocals at 180 degrees for the same song, you are left with a difficult decision of trying to improve what makes the overall presentation best. You are right in this case that there is no surefire way to know right from wrong because of inconsistent polarity in the mic array as well as the phase inconsistencies in the mic array. I did not understand exactly what you were describing in previous posts, so thanks for making it clearer for me. When recording in the studio, we would often hear the kick drum not sounding quite right coming through the console. The signal was being fed through outboard gear (compressors, limiters, gates, etc...) and the polarity which we were trying to preserve at zero was not being maintained. So we would isolate the kick track and flip polarity to see if a difference could be heard. We all heard a difference and we would generally agree that one polarity setting gave what we felt was a punchier, beefier sound. We tried to maintain zero polarity for all tracks. The example given of a kick drum/mic and a loudspeaker cone movement is often made because it is easy to visualize and to describe the phenomenon. Again, your thorough description of many different setups shows how complex of a problem multi-miking as well as stereo reproduction can be. I do feel that the recording process should seek to preserve polarity even in multi-miking situations. In the example I gave above with the kick/snare and vocal, it would be easier to decide how to handle a recording if polarity was the same for all 3 of those tracks. I believe this makes it easier to make decisions from a mastering perspective and also from a playback perspective at the consumer level for those who are aware of the polarity problem. One big experience of polarity having a big effect on music was listening the U2's All That You Can't Leave Behind. A friend who owns and runs a recording studio had come over to listen to his newly bought record and as a big U2 fan he and I were both disappointed to hear the mix sounding very flat and lacking space and with little soundstage. I stopped the recording and told him I was going to try something. I flipped the leads of the speaker cables on both speakers and played the same track. We were both amazed at how different the recording instantly sounded. The stereo separation and soundstage were both greatly improved. It wasn't subtle at all and we both looked at each other with a bit of amazement, so we knew we were both hearing the same thing. Thanks for suggesting the Parsons/Court Sound Check CD. I'm going to try and track it down and listen to the tracks you mentioned. I am always looking for good test discs. I'm curious to know if you hear a difference on track 73 and 74 when you flip polarity? Also, which do you prefer, multi-miked recordings or stereo pair/mininal mic recordings often used for jazz? Cheers, TV -- tv69 ------------------------------------------------------------------------ tv69's Profile: http://forums.slimdevices.com/member.php?userid=32022 View this thread: http://forums.slimdevices.com/showthread.php?t=69447 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
