Mic's canceling each other on playback

[c3hammer]

I've been recording with a DPA 4061 and with any other mic they cancel out much of the low to mid range when played back together. On their own each track sounds ok.

I can't seem to get any decent effects by splitting mono tracks and panning when combined with the mono from the other mics. If I put the DPA on the left and the other mic(s) on the right and monitor through headphones it sounds great. Once you try to blend them together they they turn into this hollow mess.

I can't figure out if I have the DPA wired wrong or if this is a common occurance and I'm just going through the normal newbie recording issue.

Any help would be greatly appreciated.

Cheers,
pete

[jefflester]

Certainly sounds like the DPA4061 could be wired with the polarity reversed. Does your audio editing program have an option for reversing the polarity of a track?

[Crowder]

Sounds like a phase issue?

[Fuzzyway]

"If I put the DPA on the left and the other mic(s) on the right and monitor through headphones it sounds great. "

Make sure that your speakers are not wired out of phase. If it sounds good on the headphones, the speakers should be reflecting a similiar sound.

Best,
Fuzzy

[MWM]

3:1 rule. If a sound source is 1 foot away from a mic, additional mics should be 3 feet away. Otherwise you'll likely have phasing problems. Sometimes you can avoid them by reversing the hot and cold leads (not the ground) on one mic. You can get a plug in adaptor that does that for $10 or rewire the cable end yourself.

[c3hammer]

I did find in Audacity a way to "invert" the track and it then solves all my issue with it. The only problem with that is I can't find an equivalent function in Cubase LE4 to do it on the fly so that I can hear the tracks clearly when monitoring.

Anyone know how to "invert" a track in Cubase? I think I know what to do with the wiring to change the polarity and get power to the capsule, but I'll double check that down the road.

Cheers,
Pete

[Ray(T)]

Interesting theory. I remember an article in Studio Sound years back where an engineer for one of the big rock bands was using out of phase mics a calculated distance apart (one behind the other) to increase the volume that could be obtained before feedback.

[jefflester]

Interesting theory. I remember an article in Studio Sound years back where an engineer for one of the big rock bands was using out of phase mics a calculated distance apart (one behind the other) to increase the volume that could be obtained before feedback.
The Grateful Dead did that in 1974 with their "Wall of Sound" PA. The PA was behind them and the mics *had* to be phase cancelling to avoid the feedback.

[Don Grieser]

In my Cubase LE 1 on my Mac, it's under Audio>Process>Phase Reverse.

[TonyP]

All makes sense. The headphones would be ok as your head acts as a divider, and the two signals,L/R can't actually interact to phase cancel.

[steve V. johnson]

DPA mics are very, very carefully hand made, so I'd be surprised if one was wired out of phase. #However, if you check the documentation with the microphone, it probably includes a "pin-out" diagram that will show which pin is positive, which negative and which is ground.

And -long- before doing -anything- to a DPA mic, I'd recommend that you contact DPA directly and talk with them about your situaion:

www.dpamicrophones.com

The great hopeful bit is that you hear everything well in the headphones. #That suggests that some other part of your playback system is wired with the left and right polarities reversed.

It's rare that microphones' positions in a room result in a complete cancellation of the signals on playback. #That would mean that you figured out how to position them to be -exactly- 180º our of phase. #Any other amounts of phase differences would result in -some- sound coming thru, and it would sound really odd... various frequencies would be
missing, or moving around (like a 'phase shifter' pedal), but getting them all to cancel is quite a trick.

Here, on the Shure microphones site is a wealth of #Shure's instructional materials (http://www.shure.com/ProAudio/TechLibrary/EducationalArticles/index.htm) including "Microphone Techniques for Music - Studio Recording".

I hope this helps...

stv

[steve V. johnson]

jefflester wrote, "Quote (Ray(T) @ Mar. 06 2008, 09:23)
Interesting theory. I remember an article in Studio Sound years back where an engineer for one of the big rock bands was using out of phase mics a calculated distance apart (one behind the other) to increase the volume that could be obtained before feedback.

The Grateful Dead did that in 1974 with their "Wall of Sound" PA. The PA was behind them and the mics *had* to be phase cancelling to avoid the feedback."


Unless the mics are right together, that is, "coincident," the phase cancellations will be pretty wild, so putting them behind one another, even calculating the distance will be pretty dodgy, esp. because the source (musician) will be moving around in that supposedly phase-cancelled field. #It's not something that I'd try...

Re- the Dead's Wall of Sound, I found these quotes
here ... (http://www.audiojunkies.com/blog/730/an-insiders-look-at-the-grateful-deads-wall-of-sound) #

"AJ: I've heard that the wall also acted as its own monitoring system. How was the feedback issue addressed since the band and microphones were directly in front of the wall?

"Richard Pechner:
I believe this issue was solved with the introduction of 2 B&K caps used in out of phase pairs as differential noise canceling mics."

It was a pretty cool technique, but ... for some reason it didn't really catch on... I read a lot about it at the time, but I've never tried it. It's a little hardware-intensive... http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif

stv

[Ray(T)]

It was probably the Grateful Dead the article was about - but it was over 30 years ago!

I also experienced phase cancellation some years ago working with a loud folk/rock band in a rectangular sports hall. The sound at the desk was fine. Leaning against the back wall was fine but walking back to the desk I found alternating loud and quiet areas. I put this down to sound hitting the back wall and reflecting back towards the stage. When in phase, the sound was louder. When out of phase, the sound was quieter. Short of rebuilding the venue, there was nothing I could do.
Ray

[jefflester]

Re- the Dead's Wall of Sound, I found these quotes
here ... (http://www.audiojunkies.com/blog/730/an-insiders-look-at-the-grateful-deads-wall-of-sound) #

"AJ: I've heard that the wall also acted as its own monitoring system. How was the feedback issue addressed since the band and microphones were directly in front of the wall?

"Richard Pechner:
I believe this issue was solved with the introduction of 2 B&K caps used in out of phase pairs as differential noise canceling mics."

It was a pretty cool technique, but ... for some reason it didn't really catch on... # #I read a lot about it at the time, but I've never tried it. #It's a little hardware-intensive... # http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif

stv
Here's a good pic of the Wall of Sound phase cancelling mic in action:

http://media.audiojunkies.com/pechner/grateful-dead-wall-of-sound-12.jpg

[c3hammer]

Hey Steve, thanks for the note. I bought a couple of DPA's on ebay that had Sennheiser LEMO connectors for a wireless setup. I wanted to use them for recording and maybe someday some live stuff. I've tried it on a friends guitar and when combined with his onboard pick up it sounds incredible as long as you don't face directly at the PA.

I am using a chain that looks like this:

DPA 4061 => mini XLR connector => (5v)Samson PM5 (48v) => Omega Studio => PC Laptop - Cubase LE4

I researched the wiring diagram and got it to work properly, but it seems as though the phase is backwards. It could also be that the Samson PM5 transformer I am using is doing it.

Now that I know what is going on I should be able to sort it out. I will say that when you get it wrong it can create some tones that are quite painful in the ear, litterally http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

Cheers,
pete

[steve V. johnson]

Jeff!!! #Thanks!! #I looked for a pic of those over/under mics and couldn't find one! #Excellent!

Ray(T), those are called "standing waves" and they are common when the sound levels are louder than the architecture
was designed for... #They happen a lot in small, rectangular and drywalled rooms in homes where folks have studios or rehearsal rooms. #The sound bounces off the 90º corners and 'meet' in series. #They can be readily apparent at roughly at a 45º angle to the corner. #Often they are frequency-dependent and -specific, not just related to amplitude (loudness), tho the louder the sound is, the more of them are apparent and they may extend further out into the room. #Stuff like balcony overhangs with blunt, flat faces can make new ones, too.

In folks homes it's pretty easy to break them up with some carefully targeted sound treatments.

Pete, yeah... OW!!! #Sorry about that... Thanks for the signal chain! #I'd guess that the LEMO/mini XLR connection or some connex in the Samson has a different pin-out than the rest...

I'm glad that you feel that you've got a handle on it now. #I'm not surprised that the DPAs sound great, and they should serve you really well once you have the phase relationships sorted.

Thanks for an intriguing problem, and sorry if I wandered a bit far afield with it... http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif I seem to be doing that lately...

All the best,

stv

[mandroid]

I'm intrigued, so if blue and white wires of twisted pair in the wire were swapped,

or ground is pin 1
hot+ 2 and cold - 3 is standard ,
and phase switch of 2 to cold, and 3 to hot .

and Y those together whats the output?

I'm thinking 'black box' so as to use 2
[low end, cause thats where I am]
SD plugged in and one cord out of the box.
wonder how the wiring in the box would be.

and of such a placement that they must be right next to each other,
as in the GD example..

Hmmm
http://www.mandolincafe.net/iB_html/non-cgi/emoticons/rock.gif

Addendum : happened to borrow the GD Movie 2 disc DVD
on the 2nd extras disc they go thru tracks in isolation
when the phase canceling Cap mic pair is left to stand on its own the sound quality is not there.
and singer has to be using the mic like lipstick, right up on it, too.

When all combined with the 3 semi trucks of gear at those big shows,
the hard party-ers out in front didn't seem to notice.

[c3hammer]

Have any of you folks played with this phase thing at all on your recording setups? I'm finding that phase can be quite an issue. I'm finding roughly the following, so far.

Mic1 Left, Mic2 Right = beautiful full warm tone in headphones, yet mud with no space when played through speakers.

Mic1 panned hard L/R, Mic2 center = fat tone front and center, but not very pleasant. It's like the second mic should get a piling on penatly flag http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

Mic1 panned hard L/R, Mic2 center, Mic2 phase changed = hardly any sound at all from either channel.

Mic1 panned hard L/R, Mic2 center, Mic1 L or R channel phase changed = Very spacious warm tone, but can be painful deep in the inner ear yet without clipping. Also one output channel with show much lower output yet it sounds balanced in head phones and through speakers.

Might any of you have some suggested reading on this subject and how to set up mastering with two mics so that you get a full, well rounded, spacious tone?

Cheers,
Pete

[steve V. johnson]

Here are some titles from the Mix Bookshelf site. #I don't necessarily endorse Mix Bookshelf, but it's one place where I know I can find a bunch of instructional and reference titles on recording. Of course these and others are available elsewhere. I've seen some on Amazon's site, too. Various searches on "microphone techniques" or "studio recording techniques" will
net you some good information, too.

Huber, Runstein, "Modern Recording Techniques, Sixth Edition". # It#is a standard for audio educators. # # Here. (http://musicbooksplus.com/bmodern-recording-techniques-sixth-editionb-p-5758.html?osCsid=8278739a19446e47b8b8e9fccf9c0c9c)

Huber, Williams, "Professional Microphone Techniques". #Very useful, one of my favorites. # # Here (http://musicbooksplus.com/bprofessional-microphone-techniquesb-p-1396.html?osCsid=8278739a19446e47b8b8e9fccf9c0c9c)

Here's (http://musicbooksplus.com/advanced_search_result.php?osCsid=8278739a19446e47 b8b8e9fccf9c0c9c&search_in_description=1&keywords=microphone+techniqes&osCsid=8278739a19446e47b8b8e9fccf9c0c9c&x=7&y=18) a search of Mix Bookshelf on "microphone techniques". #There are lots of titles, and I apologize that I haven't gone thru more of them for you.

The first two are the ones that I more usually pass on to folks new to the field.

Stereo mic techniques and phase relationships is a pretty basic topic and so it should be addressed in about any of the ones about recording basics. #

I don't like to have the extra variables, so I prefer to single mic stuff, or alternatively, to use a single-point stereo mic, so I have several of those.
I much prefer to check the phase relationships of the various mics/tracks as part of the mixing process than to have to figure the phase relationships among multiple mics as I'm tracking and then to have to re-check all those spatial relationships again later. #But that's just me. #Others do great work
with multiple micing, both close up and using spatial relationships in the room creatively.

Phase relationships among any two sound sources can be used very creatively and can bring all kinds of textures to audio recordings. #Usually, it's good to know how to get them working naturally, and then to mess 'em up, but ... the rule is, there are no rules, and phase relationships can be a rich field and set of tools for creating sounds.

I hope this helps...

stv

[c3hammer]

Thanks Steve! That should keep me busy for quite some time, LOL! http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

Cheers,
Pete

[david blair]

I have experimented with using two mics and a line out from the effects loop of each to the input of the other with great results, seemingly immune to feedback even when looking right at a speaker.
This idea is also now a breakthrough in MRI imaging and also has some interesting possibilities for electricity harvesting.
the fat man rocked!

[steve V. johnson]

Hey David,

This sounds really intriguing. #But there's something missing, for me, anyway.

What comes after the mic, that is, what has the FX loops? # Are the FX loop jacks XLRs (not likely...?), TRS or TS 1/4" ?

If it's TRS ("tip/ring/sleeve" meaning that it's set up for stereo male 1/4" plugs), do you put it only in part way, to the first
click (called "half-normalled")? #

Where exactly does the FX loop cable go then? #Does it go to the -line- input of the other mic's channel? # Or... where?

What's "electricity harvesting" in this context?

And, finally... who's "the fat man"? http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

Thanks for an interesting idea, and for answers to the above.

stv

[Shelby Eicher]

Certainly this can be an issue using 2 mics. I've solved this problen with switching the polarity on one of the mics. I often wondered if this is what happen on Andy Leftwich's solo CD. You can here every instrument plainly except his mandolin and fiddle. Generally I would say it's a bad mix but I know that he and all the guys that recorded and mixed that CD have to know what they are doing. He's an awesome player but I have trouble listening to that CD because of the final product. Has anyone else wondered about this.
Shelby

[david blair]

the fat man=jerry garcia
there is a website out there describing the wall of sound set up and also the stereo return/effects loop for his guitar. he could control the effects blend from the guitar.

loop from your effects out to the input of the other mic, each direction.
i'm using a pendulum sps-1 pre. Maybe a single trs cord for send and return of both channels would work.

[steve V. johnson]

david,

Sorry, you've lost me completely... I'd like to understand what it is you're suggesting, tho.

stv

[david blair]

Hey Steve, all
The way I understand the idea of phase canceling is that this is different than using a phase inverter (changing the signal direction of the send and return). Phase canceled mics should be a matched pair of figure 8 polar pattern. They are in phase (wired the same direction) but placed perpendicularly. This somehow "cancels" sound from particular directions, simulating a cardioid or hypercardioid pattern, with the additional bonus of a proximity drop-off effect. Anyway, it reduces feedback for me when I send an aux line out of one mic to the other, and vise versa.
electricity harvesting= not a complete hijack of this thread. It does use an acoustic pre-amp.
Lots of reading at this company site, a supplier to many familiar names in the studio.

http://www.analog.com/en/

Besides working as instrument pickups piezo crystals have many other applications such as electrical generating transducers or dampening tiles on a space shuttle or a downhill ski, for instance. They can send a current when vibrated or contract/dampen with a current applied. This is what happens inside an electret-condensor microphone, too. Careful signal processing and voltage regulating with a system of diode/capacitor/ohm matching/RMS (root mean squared) processing/to an inverter/amplifier is what I'm suggesting. I came to think about this with an idea that a varnish layering system similar to a semiconductor would work as a pickup on a mandolin. Recently developed piezo devices are thin, flexible, and work best when induced into the shape of an arch. These CAN BE PLACED IN AN AUTO TIRE and generate power/current enough to never slow down or plug in. I would make this an open source patent but General Electric and Nasa got it last month. Their patent confirms my theory completely and details a few other slick things too. Unfortunately they still want us to buy gasoline.#
So there you go, my crazy ideas.

What are your favorite microphones?

[steve V. johnson]

Wonderful stuff on the harvesting, thanks! #I've read a little about crystal generation, but not recently. #Thanks!

Now... about this...

"Anyway, it reduces feedback for me when I send an aux line out of one mic to the other, and vise versa. "

I'm still struggling to understand

1) the signal path you describe and visualize it, and

2) how using aux sends/returns back to a channel eliminates feedback.

Sorry if I'm being terminally dense... it happens... http://www.mandolincafe.net/iB_html/non-cgi/emoticons/tounge.gif

Thanks,

stv

[Spruce]

"I often wondered if this is what happen on Andy Leftwich's solo CD. You can here every instrument plainly except his mandolin and fiddle."

If ya'll want to hear an example of phase cancelattion on a famous recording, go check out The Band's 2nd LP--the brown one with "Cripple Creek", etc. on it....

The piano was apparently recorded with 2 mics that were out of phase, and sounds OK in stereo. #
But in mono, the piano notoriously disappears, which it did on mono radio stations all over the country...

When recording using more than 1 mic on a source, I usually run the board in mono to prevent this sort of thing.

It's a great way to work, and makes it sound so much better when you pop on the "stereo" button... #http://www.mandolincafe.net/iB_html/non-cgi/emoticons/wink.gif

[steve V. johnson]

I'd forgotten about the Band thing! #LOL!!! #Thanks!

I always start my mixes in mono, and check 'em in stereo. Then as it progresses, that reverses so I'm working in stereo and
checking in mono. # Really weird things can happen with time-based effects (chorus, flanging, doubling, delays) when they
sum to mono! #Sometimes they're very cool, other times they're just ... incongruent. #http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

stv

[david blair]

The pre-amp for electricity harvest is essentially the same design as those used for audio applications. Understanding this may be of interest for anyone desiring to modify or make a pre=amp for phase canceled signaling.
An electromagnetic or piezo-electric signal is first poled, then oriented through a diode (one way current) #and buffered to match ohm ratings (think high or low Z) with a rheostat. This is a feature sorely lacking in most systems. Martin Taylor uses this when blending any of three pickup/mic signal combinations on his guitar. Anyway, if you're still with me, the "phase canceling" occurs when signals which have carefully matched ohm ratings are aligned, in phase. Just like the familiar problem of a mic hearing itself from the speaker and feed-back, except in this example the identical characteristics of the two or more perfectly matched signals create a "standing wave" and disappear. A unit like a digital feedback eliminator works constantly calculating a root/mean/square (RMS) equation throughout the harmonic range while summing signals, canceling as it works. #Then of course amplification and/or power inversion. A phase inverter switch on your soundboard simply changes the direction of signal travel along either two wires, the third being a ground.
I never thought you were slow to understand before. Usually quick with valuable experience to share. Thanks for that.
here's a pick of my pre=amp. The "inserts" are TRS. So, channel out jack each side to insert of the other, each direction. A single TRS patch cord would likely work even better, But I don't have one yet. The Pendulum SPS-1 has exactly matched ohm signals...

[steve V. johnson]

Thanks for your kind words about my postings. I hope to have some information of value to others.

I really have never heard of using inserts or aux sends/returns as you suggest, so I went over to the newsgroup rec.audio.pro
and asked those folks for comments on your posts here. I think that I posted accurate excerpts of your posts there. If what I
shared there was inaccurate, I apologize most wholeheartedly.

I'm not qualified to comment on the statements you made here. I don't understand them at all. As re: "harvesting", that all sounds good to me, tho I have no facility for confirming nor denying the technologies you mention (nor do I wish to... I'd much
rather believe it). The audio parts I just do not understand at all. Non-sequitur to me. Sorry. I can be very dense at times.

In any case, here are the comments from rec.audio.pro:

http://groups.google.com/group....bfb750d (http://groups.google.com/group/rec.audio.pro/browse_thread/thread/65aa5c97df40b40c/5b4f89c8dbfb750d#5b4f89c8dbfb750d)

stv

[david blair]

Interesting posts over there, Steve. I am available for personal contact, and personal remarks are best directed there.
I "harvest" electricity from a crystal every time I plug in a piezo pickup or microphone and amplify it to a speaker. It does seem strange to think of running a system like this without an outside power source, but the patents are rolling in daily from people like Toyota and GE. The use of phase canceling has been also a major development for MRI imaging, now providing a clearer, more focused picture. I only bring up these topics as a point of interest, they continually overlap with our subject, quality sound.
phase cancelling=two or more signals "in phase", pre amplification
phase inverting=changing direction of the signal, after pre.

#Phase canceling is for me a fascinating subject. Defining the relationships between impedance, voltage, watts, and amperage can be challenging. Pre-amp devices with precision components now make for a "tunable" device. More fascinating yet is that the best results are integrating math and harmonics, geometry, and intervals computed from musical scales. Crazy?
#Thanks again for the "feedback", but I much prefer mine before amplification.