Spaced pairs - matched mics or unmatched?

[Ivan Lee]

Hey All,

For many years I have been recording acoustic (fingerstyle and singer songwriter) with a spaced pair of unmatched mics - Gefell M300 on the treble side and Lawson L47MP on the Bass. I recently had a need to use the Lawson on vocals at the same time (getting more into recording everyone playing and singing as opposed to separating everything) and put up the 2nd M300 (matched pair) for the Bass side.

To keep on the "safe" side I also put up a Gefell M990 right above the second M300 (cardioid large Diaphragm - closest thing I have to another Lawson) and I noticed a lack of fullness in the Bass right away with the pair of M300s. But at the same time they sounded very nice and clear. So I looked at the frequency spectra of the M300 and M990 and saw that the Bass indeed rolled off a little bit more and earlier on the M300s.

I added a small rise starting at 100Hz on the second M300 to compensate (shelving with a very gentle slope (EQ7 from ProTools)) and after that I found it pretty hard to tell the difference (will of course double check this with fresh ears today...). Just starting on this recording project so will be listening a bunch more today but figured I would post this and welcome any comments or others preferences for matched or purposely unmatched spaced pairs...

[KevWind]

For a number of years I had a pair of Shure KSM 44 's which I thouht did a reasonably good job on acoustic.

But I ended up selling them to fund purchasing 1. Schoeps CM6 -MK4 and 1. Brauner Phantom V which is what I use now. So I was not able to compare the difference side by side on the same performance so I can't say for sure I have a preference. I will say I am completely happy with my current setup

[sdelsolray]

The bass rolloff of the M300 is minor (starting at 100Hz, down 2dB at 50Hz) and won't have much effect on acoustic guitar. Still, it does mitigate the proximity effect a bit. The M300 is a wonderful mic. I suspect you are hearing a more accurate recording of your guitar with the pair of M300 than with one M300 and one LD mic.

On another point, I've noticed over the years that not all cardioid pattern mics are the same when it comes to the proximity effect. Some exhibit it more than others at the same distance from the source, and vice versa.

One trick I use to "tighten up" the bass of a recorded acoustic guitar is to use a high pass filter on the tracks (e.g., a corner frequency of 65Hz with a slope of -12dB per octave). That cleans up the low end and removes subharmonics from the instrument.

As to matched or unmatched pairs, both can yield excellent results. However, purists claim that a matched pair generates a more true stereo field than an unmatched pair, moreso in the diffuse field than in the free field (for acoustic guitar).

[rick-slo]

I have a matched pair of Gefell M300s. That said, matched pairs are not needed in a spaced pair set up. It is more appropriate for coincident mic'ing (such as XY) where you have a narrow soundstage and you don't want different frequency notes appearing to come from slightly different places in the soundstage (due to uneven frequency response between the mikes) - that said the frequency response in a given brand and model of most mikes these days is consistent enough that matched sets are not usually needed even in coincident mic'ing.

[Ivan Lee]

I have done some more work on this and maybe have a new insight for myself. I am much more in agreement now with those who implied that the freq rolloff difference should have very little effect on Acoustic Guitar.

I started from square one again since the previous days recording was done pretty close to the mics ~6 inches or so and widely spaced. The notes on different proximity effect above ring kind of true for me now. I listened to each mic individually to get a good sound. I ended up with the mics about 15 inches apart and about 9 inches out. The treble one is a little higher and not surprisingly aimed about the 12the fret and the Bass one is aimed at the back of the bridge. Both are aimed straight ~90 degrees from the plane of the guitar.

After this work I recorded a quick bit of playing (truly not CD ready but does show the sound). This time - No EQ (see below - HPF at 63Hz on Master) but a small amount of phase correction for any asymmetry in mic distance (Waves InPhase today) - did not change much from the uncorrected audio but it is a nice shift in both of the files. This time with no EQ - I can honestly not discern a difference between the two. I did the phase correction because I heard no difference in the uncorrected files either. Tried speakers - headphones... maybe hear a little something but not consistently. I am posting the phase corrected files just to share what I am hearing and to see if someone else gets a different view. 24bit, 96kHz no compression but a little reverb. Phase correction was almost identical 33 or 36 sample shift of the Bass side mic. NPNG preamp on all mics.

I did forget that I added a HPF (ProQ) at 65Hz on the Master Fader. Mostly was just to clear up any garbage down there. Again - this made no difference in what I heard. I always loved the M300 on the treble side and this test has only broadened my appreciation for these mics. :-) If anything I hear the slightest decrease in Bass with the M300s and a slight bit of higher end focus/detail. This may also be because I know the M300s have more treble rise in them and now I am hearing two of these instead of just one (the M990 is pretty flat to about 6 or 7kHz whereas the M300 starts its treble rise at 3kHz. I doubt I would hear this consistently in a double blind test though. I am a little surprised I don't favor the lg diaphram one but thats just how it falls out today...

M300 M990
https://drive.google.com/open?id=0Bz...jNoMnIxVTMtTnc

M300 Pair
https://drive.google.com/open?id=0Bz...i1oN1FGSVpOMU0

[rick-slo]

M300 pair clearer and more detailed than the M300 M990 combo. I prefer it. Like I said, I have the M300 mikes. I also have the NPNG preamp. I have a lot of recordings using the M300s but the last few years have been mostly using my Gefell M295s. The M300s do have a pretty pronounced proximity bump, so mike position is important in this regard.

[Doug Young]

Hey Ivan, nice playing and good sound. I also slightly prefer the m300 pair, tho it's not night and day, and either one would be fine if we weren't comparing.

Just a few thoughts - your recording levels are really low. Not a big issue, since the recording is clean and quiet, but you're at at average of -34 db, with max peaks at -15db. Might be easier to work with to come up a little. I'm not clear on what you did with the time shift, but I see a consistent phase shift of 20 degrees or so, about 22 samples off between sides. I corrected it, and don't hear any huge difference, so not a big problem. I'm not sure if this means you over-shifted or didn't shift enough. To me, the recording sounds really nice, but it doesn't sound quite as wide or dynamic as spaced pairs, more XY-ish. Did you pan the channels inward or anything? Might be my imagination.

In any case, all just nits and questions, this is a really nice sound!

[Ivan Lee]

Thanks to both of you for taking a listen and commenting back (as well as the others that took the time to weigh in)!

I also am liking the M300s and think I will go with that for a bit. WRT levels, I have been playing with recording through a Charter Oak SCL1 as well in the path but of course left this off for the Mic comparison. The SCL1 is an amazing box but just tonight after doing all the mic setup and getting levels ready for take one... I am finding for solo guitar and working by myself - no compression is sounding better. Can always add it after the fact...

WRT the phase shift this may be me not fully understanding the Waves plugin. It was a manual process and I probably need to refine my understanding of it. I usually use the Sound Radix one which has an auto analyze and fix mode but I didn't have it installed in the system at this time :-). Will look at that a bit more.

In the meantime I am starting back at getting some real takes done. Will post a link when I send it up to youtube...

Thanks again!

[ChuckS]

I listened several times through my monitors. I enjoyed your playing and the recordings are very nice. I have a slight preference for the pair of M300s. I'd be curious to hear that pair recorded a bit further out. Have you considered micing out 16+" and with 22+" separation between them, panning hard right and hard left? I guess part of the choice is whether you are going for a specific sound or whether you are trying to capture your guitar as realistically as possible.

[Ivan Lee]

What great input... I moved the mics 16" apart and me 14" back to start and man does that sound better to me already (night and day really!)! Will have to continue to search out what might be optimum but already this sounds way better. I threw in another take with the SCL1 patched in and now I am liking that as well (only ~3dB peak reduction). Just a HPF at 60Hz and a little reverb.

Here are the files (once again - not a final take yet :-)...
M300 16"apart, 14" back
https://drive.google.com/open?id=0Bz...1BKTHlvdUI3ZkE

M300 16" apart, 14" back, SCL1 in
https://drive.google.com/open?id=0Bz...Ed4eEFZaEM0a2M

[ChuckS]

Sounds really nice to me. It seems less forward/close and more natural. For whatever reason, I prefer the recording without the compressor/reverb. But, your recordings are all nice, depends on what you like. That's also a very enjoyable song to listen to. Thanks for sharing.

[sdelsolray]

Originally Posted by Ivan Lee

What great input... I moved the mics 16" apart and me 14" back to start and man does that sound better to me already (night and day really!)! Will have to continue to search out what might be optimum but already this sounds way better. I threw in another take with the SCL1 patched in and now I am liking that as well (only ~3dB peak reduction). Just a HPF at 60Hz and a little reverb.

Here are the files (once again - not a final take yet :-)...
M300 16"apart, 14" back
https://drive.google.com/open?id=0Bz...1BKTHlvdUI3ZkE

M300 16" apart, 14" back, SCL1 in
https://drive.google.com/open?id=0Bz...Ed4eEFZaEM0a2M

I wasn't in your room when you recorded these, but I suspect these recordings are more accurate than the earlier ones you posted. i.e., they sound more like the actual guitar. Moving the mics further away allows the mics to pick up a more balanced sum of the guitar's total output instead of favoring highlights of the sound coming from the small area of the guitar at which they are pointed.

I don't know anything about your room or how you might have it treated. Still, now that you have a pair of M300, I would suggest a whole series f placement and configuration experiments, e.g., X/Y at several distances, X/Y directly in front and slightly towards the headstock, OTRF (same), etc.

Very good playing, by the way.

[Ivan Lee]

The experimenting did continue after I posted the last audio :-). I next went to 22" apart and 20"back. The stereo field continued to widen but the change was more subtle than the first shift to 16" 14". I am still experimenting with where to settle in with the spaced pair approach but somewhere around 18" to 24" apart and about the same back looks like the right ranges.

As I do this I remember the old barely treated days of this less than ideal recording space. Room is ~24' long, 9'wide and between 7.5' and 7' tall. The advantage of this room is that it is mostly underground, not needed for any other purpose and is the quietest space in the house. The disadvantages are about the same :-). I am putting in some pictures so you can at least see (if not hear) where I am working.

So... as I move the mics apart and myself back I am now seeing much more possibilities of first reflections hitting the mics. I created sort of a dead area with panels both on the wall and ceiling but this also has the rack on my left and a computer monitor on my right. You can also see two big Gobo panels I can use to help but here is the next question. Since I record alone a lot, where is the best place for access but not interference from the Rack and Computer monitor? I also did a lot of playing yesterday facing different directions and at least for me was liking the hint of non-dead space by facing out down the long end of the room.

I welcome any thoughts others have on this :-)

[sdelsolray]

Ivan,

Are you recording in that space between the rack and computer? Have you recorded at other locations within your room?

[rockabilly69]

Originally Posted by sdelsolray

Ivan,

Are you recording in that space between the rack and computer? Have you recorded at other locations within your room?

that exact thought crossed my mind, a little congested to say the least But, I like his latest recordings!!! Good player, good tone!