One consistent recommendation was the Schoeps line of microphones. I was lucky enough to find a deal on a pair of used Schoeps CMC64s (CMC6 modular bodies and MK4 cardioid capsules) a few years ago, and even though they were fairly expensive I bought them because I knew that once I had a pair of Schoeps, I could no longer blame the microphones for my less than satisfactory results.

Now, a few years older and hopefully wiser, I have come to realize that the difference between most mics is pretty subtle, the difference between preamps and a/d converters is even more subtle, and the big differences come in the instrument, the performance, and the room. Of course, believing that equipment has a minor impact has not kept me from buying more gear. Mics and audio interfaces, monitors and headphones, sometimes I just can’t resist trying something new.

A New Toy (er, Tool)

Since I’ve discovered the fun of videography I’ve found even more gear to consider. The recent Homebrewed Music comparison of stereo mics for the Kodak Zi8 stimulated my interest in a microphone that is widely recommended as an excellent medium priced tool, the Rode NT4. This mic combines the two capsules and electronics of the Rode NT5 small diaphragm condenser in a single body visibly similar to the NT3 model. This mic includes the option of using a 9 volt battery for power if 48 (or 24) volt phantom power is not available. It also comes with adapter cables providing either a conventional pair of XLRs or a 1/8″ stereo miniplug for cameras and field recorders. The NT4 doesn’t come up on the used market very often, but with a little patience I found one at an attractive price and added it to my collection.

One thing about high end (that is, high priced) gear like the Schoeps mics, in my little home studio they tend to stay in the drawer. Since Schoeps prices have gone up steadily for the last few years, my mic collection has become an investment as well as tool set, and I’ve become a bit protective of the “good stuff.” If I need a mic for a quick recording, I’m much more likely to pull out a less expensive unit, and the NT4 has been getting plenty of use lately. It’s simple to set up, useful with various recording systems, and sounds pretty darned good to me.

Shootout Time

In fact, it sounded so good, I started wondering how it might compare to the hallowed Schoeps CMC64. Once I listened to them side by side, would I still think the NT4 sounded darned good? I’ve gone into some detail on the procedure needed for a meaningful mic test, and I’ve done some other comparisons. But a recent flurry of “what is the best mic” postings on various guitar forums triggered a desire to evaluate the Rode and Schoeps side by side.

Naturally, I set the mics up as close as possible to the same position, using the same stereo arrangement. The Rode is constructed as a fixed X-Y array, so I used a stereo bar to mount the CMC64 pair in the same configuration.

Schoeps CMC64 and Rode NT4

I connected both mic systems to the Echo Audiofire Pre8, and set the gain by eye. Next I setup Reaper to record two stereo tracks, and applied the Sonalksis FreeG meters to each track. This excellent plugin let me know that my preamp gain settings were within a couple of db of each other, as close as I am likely to get with the small gain controls of the Pre8. After recording, I pulled the files into Adobe Audition where I use the Group Waveform Normalize function to set the perceived average levels to – 12 dBFS.

It’s All in the Listening

Just listening to the tracks they sounded pretty similar, so I pulled the tracks into foobar2000 to use the ABX utility. Under this audio microscope I quickly discovered that I could recognize the files as different. The Rode recording was very (and I mean very) slightly “lighter,” less full than the Schoeps track. When I checked the frequency response curves I saw that the Rode had a reduced bass response and more pronounced emphasis on the highs compared to the MK4 capsule of the Schoeps.

NT4 frequency response showing low cut and high boost

CMC64 frequency response. more linear than the Rode

I immediately wondered if I could reduce the difference with some EQ. Back into Adobe Audition, where I used the Parametric Filter, adjusted to the opposite of the Rode frequency response graph, to process the Rode track and save it to a new file.

After this processing, I could no longer tell the files apart when I ran ABX in foobar2000. In the first test I made six consecutive correct choices with no incorrect ones, a better than 85% certainty that I could tell them apart. When I compared the Rode file with EQ to the Schoeps file, my results fell apart, with three incorrect choices out of four tries.

Based on this test, it seems that a little digital EQ can make a Rode NT4 sound like a Schoeps CMC64 when recording me playing solo acoustic guitar (in this room on this day). This is not to say that an NT4 is “as good as” a pair of Schoeps mics, of course. The Schoeps modular system supports many different capsules for different pickup patterns and uses. And a pair of mics give much more flexibility in placement than a fixed X-Y stereo mic. But in this one very limited use, simple stereo recording of a solo acoustic guitar, the NT4 reduces the complexity and cost while delivering sonic results that I find completely satisfactory.

Try for yourself. Here are the files (these are CD spec 44.1 khz 16 bit PCM wave files, so they’re large – about 14 Mb each):

Download O.wav
Download P.wav
Download Q.wav

One of these is the Schoeps, one is the Rode without EQ, the other is the Rode with EQ. Ideally you’ll use an ABX tool to listen carefully and determine if you can tell the files apart. However you choose to listen, post a comment here with your impressions and I’ll email you the identity of the three files.

***** June 17, 2010 Update *****
When I posted links to these files on the Acoustic Guitar Forum the folks there quickly zeroed in on the Schoeps CMC64, so I went back to foobar2000 ABX and, sure enough, once I found the right place to listen, I could hear the difference between the Rode, even with EQ, and the Schoeps. Which goes to demonstrate an important aspect of ABX testing – it’s quite possible to miss differences, due to tiredness or predisposition or some other cause.

By separating the mic from the camera, I should be able to position the mic for optimum sound while placing the camera for the visual effect I want. Of course, I can do this wihout an audio input on the camera by a technique called parallel recording, that is, recording on a separate audio system of some kind. The familiar clack of the slate at the start of a movie sequence is used to make it easy to synchronize the picture and sound, and this technique works very well for my homebrewed videos as well. Still it’s very tempting to think that recording directly to the camera is an easier way out, with camera audio every take and every edit lining up without any extra effort.

I’ve been interested in the range of options for attaching a mic to the Zi8, and back in December I went on a little mic shopping binge. Between my storage drawer, Ebay, and Sound Professionals I gathered a collection of mics in a range of prices. But I was struck with a glitch in my Zi8 audio, which required several round trips to attempt repair at the East Coast contract repair depot. Eventually Kodak agreed to replace my camera, but by then I was on a lovely trip to Hawai`i.

Test Design

Now that I’m back I’m ready to offer up some test clips. At first I planned to video a number of brief samples of guitar and vocal, which was very troubling to me. I strongly believe that audio sampling should be done with a single performance and carefully volume matched, in order to reduce the number of variables in the sample. As much as we think otherwise, humans just cannot judge subtle (or even not-so-subtle) differences without careful controls. My aha moment came when I realized that I was only testing audio, not video, so I could use a recorded source to get a repeatable performance. Focusing on audio only also allowed me to upload the much smaller audio clips, so the comparison will be quicker and easier.

For level matching I decided to take the easy way out and simply normalize the files. Normalizing raises the peak of a file to a given level, in this case I chose -3 dBFS. I adjusted levels like this so our ears won’t be fooled by level differences, but these samples hide the differences in the real recording you’ll get if you use one of these mics. So I’m including the original sample as well. Remember that I adjusted the sensitivity of the Zi8 for each mic, so the volume levels are affected by that even in the original, un-normalized samples.

I first created a test recording in Reaper, some slack key guitar naturally. I recorded in mono with an Audio Technica AT4050 in cardioid pattern. Then I added a bit of narration. All camera mics I know about, and many accessory mics as well, are omnidirectional. There are plenty of reasons why an omni is a good choice, but real trickery is required to get a good stereo image with omnis. So I threw in a bit of movement in the stereo field to evaluate channel separation. I arranged the narration and the stereo test ahead of the music and adjusted levels.

I placed all the mics very close to my normal listening position and played back the test recording through my normal monitoring chaing – Echo Audiofire 8, Hafler P3000, Dynaudio BM6p. A Radio Shack SPL meter showed 74 db C weighted at the mic position.

As I mentioned, I adjusted the sensitivity of the Zi8 for each mic. In each case I adjusted the sensitivity to the highest level that did not show any red. I label the default sensitivity as 0, lower sensitivity goes from -1 to -5 and higher goes from +1 to +5. I wound up using the whole range in this comparison.

Test Clips

Here’s the reference recording. It won’t get any cleaner than this.

or download ref.mp3

I used the Zoom H2 as the mic in my first experiments with the Zi8, so I included it in this comparison. It’s also handy because we can record with the H2 and the Zi8 at the same time. Even though the signal in the Zoom was very low and pumped up with a lot of digital gain in the normalization process, it is quite a bit cleaner than the Zi8. I set the Zoom to M Mic Gain because tests have shown that the H setting adds noise. This still resulted in a rather low level, so raising it also raised the noise as well.

or download h2p.mp3
Original versions, no normalization:

or download oh2p.mp3

I used the rear mics on the H2 so I could operate the controls on the front of the unit. As a result the stereo left and right are backwards in both the parallel clip and the Zi8 clip. Here’s the output of the H2 headphone jack recorded on the Zi8 with sensitivity set to -3.

or download h2v.mp3
Original versions, no normalization:

or download oh2v.mp3

If you’re like me you’ve been fooling with recorders for a while, maybe going back to cassette tapes. Perhaps, like me, you have some kind of little mic in a drawer somewhere. My drawer mic is labeled www.reactivesounds.com but the web site is a dead end now. I bought this to use with my minidisc recorder a few years ago. The mic is omni, no cable (requires an female to male extension), and has been repaired with superglue. I used -2 sensitivity for this mic.

or download drawer.mp3
Original versions, no normalization:

or download odrawer.mp3

I’ve used Sound Professionals http://www.soundprofessionals.com/ for these kinds of recording gear for years. I used one of their T-mics for years with my minidisc, but somehow lost it. They still sell a mic with the same model number, SPSM-1, but it doesn’t look much like the mic I remember. I set the Zi8 to -3 sensitivity for this mic.

or download spsm-1.mp3
Original versions, no normalization:

or download ospsm-1.mp3

The SPSM-15 is the least expensive single point stereo mic sold by Sound Professionals. It appears to have a higher low frequency cutoff than the SPSM-1, and/or lower sensitivity. As a result I set the Zi8 sensitivity to -2.

or download spsm-15.mp3
Original versions, no normalization:

or download ospsm-15.mp3

The AudioTechnica AT825 has been a popular single point stereo mic for many years, but was recently discontinued. The replacements are much higher in price, so it might be worth watching for used examples of the AT825 on Ebay or Craigslist. It seemed perfectly matched to the Zi8 and worked well at the default sensitivity setting.

or download at825.mp3
Original versions, no normalization:

or download oat825.mp3

I was impressed with the performance of the AT825. I was very disappointed in the AudioTechnica Pro 24. Although it looks much more impressive than the T-mics from Sound Professionals, it was very low in output, requiring that I set the Zi8 to the maximum +5 sensitivity.

or download atpro24.mp3
Original versions, no normalization:

or download oatpro24.mp3

Let’s Look at the Video

Let’s finish off with some actual video. Be careful with comparisons, but perhaps there will be some blatant differences we can take away. When I framed the shot to include the whole guitar the camera wound up about 5 feet from the instrument. I adjusted the Zi8 sensitivity for each mic using my normal procedure – the highest setting that did not show any red squares.

I had a little fun with my new Edius Neo 2.5 software putting together a compilation of the mic demonstrations.

All these mics sound better here than in the audio test with the recording, but they still show their basic characteristics. The camera mic picks up a lot more room, as it must at that distance. And since the room is a boxy little thing, the recording sounds small and boxy.

The H2 in this clip is very slightly overdriving the Zi8, to my ears. The slightly dark voice of the H2 comes through as well. The Sound Professionals SPSM-15 does a pretty decent job for very small bucks. I failed to mention in the video that the sensitivity on the Zi8 is down to -3. This means the SPSM-15 is quite sensitive, so it might be a problem if your source is loud. To my ear the AT825 is the winner. I like the clear presentation. I’m sorry I didn’t do a better job of balancing the channels.

I hope these comparisons are useful. I plan to try these mics with a different camera in a future post.

For a number of years builders have worked on more stable replacements for the wood in our guitars, and now we have plywood, aluminum, and a range of composites including fiberglass, kevlar, and carbon fiber. In fact one of the pioneers in carbon fiber guitars, Rainsong, started their business in Hawai`i and attracted a number of local players to their instruments.

Composite Acoustics is a relatively young company that started with a dreadnaught and bluegrass focus, but thanks to my encouragement (hey, I wrote them an email) they’ve developed some very fingerstyle friendly models, especially the new OX body style.

I’ve been very curious about the Composite Acoustics OX since I saw the first pictures, and when I found a used one offered in one of the guitar forums I visit, I snapped it up. Here’s my new baby in all its carbon fiber glory:

An old leather strap holds up the high tech carbon fiber OX.

The body on this beauty is pretty slick, so the soft old leather strap helps hold it in position. Note the perfectly smooth and comfortable (if graceless) merging of the neck, body, and cutaway:

The neck flows smoothly into the body

I like the simple detailing on this very reasonably priced guitar. The tuning pegs are some I’ve never seen before but they work nicely. I would prefer a bit lighter peghead, but that’s true of almost every guitar I try:

The tuners are attractive and work very well

The black woven look of carbon fiber is so hip now that you can buy fake carbon fiber decorative parts for your car or motorcycle. The drama is evident in this shot of the top of the OX. This is the simplest, least expensive finish offered by CA, they call it Raw. The bridge, saddle, and bridge pins are all fabricated from composites. The sound hole decoration is a thin sheet of brushed aluminum that floats above the weave. You can catch a glimpse of the Wittman Mini tuner peeking out of the soundhole. I’ve installed these in almost every guitar I own:

Dramatic weave of carbon fiber, a Wittman Mini tuner in the soundhole

I was hoping for a lot when I bought this guitar, and I’m not disappointed. I think Composite Acoustics has figured out a bunch of stuff very well to create the OX Raw. Here’s a bit of video, an old hula song called Papalina Lahilahi showing some of the fun of playing this lovely instrument:

The guitar is tuned to taropatch F, open G tuned down one whole step. From low to high: C F C F A C. The sound on this video was recorded on the Zoom H2, you can see the top of it just edging into the bottom of the shot. I pulled the audio file into Adobe Audition and tweaked the EQ just a bit, but there’s no reverb, compression or other effects, you’re hearing the sound of the guitar.

The only bad thing about finding a nifty new item like the OX is the sudden urge to explore other Composite Acoustics instruments, like that cute little Cargo travel guitar …

I’ve tweaked and fiddled with this guitar for a while, especially since I brought it to O`ahu. The humidity is pretty tough on instruments. The tuning machines have always been stiff and they’ve gotten worse lately, so I decided to swap them out for the new Grover Vintage Sta-Tite 18:1 machines. I’ve heard great things about these machines on various guitar forums, and the measurements looked right to be a drop-in replacement for the stock tuning machines. I ordered up a set of #4592 Grover 18:1 Sta-Tites from Stewart-McDonald.

Well, for once luck was with me, and in fact they work and look like they were made for this guitar. Screw holed lined up, the shaft diameters are different but the bushings that came with the new Sta-Tites fit right into the old holes. Here’s a pic of the back of the peghead with half the machines replaced:

Epi Peghead with old and new tuners

These new machines are basically totally different from the originals. The base plate is thicker, the gears are obviously different to provide the higher gear ratio, and the attachment of the gears is totally different as well.

Here’s the original tuning machine:

Original Epi Grover Tuning Machine

Part of the difficulty in turning it is due to the warped base, the rest because the curved arm that holds the shaft has bent, releasing the mesh of the right angle gears.

Here’s the new one:

New Grover Sta-Tite 18:1

Notice how solid and thick the base plate is, and more importantly notice that the shaft is held in a cast mount, a much more solid bit of engineering.

These tuning machines have another fine virtue, they’re not terribly expensive. I bought this set from Stewart-McDonald for $37.37 – I’ve already gotten my money’s worth the first time I changed strings.

As I expected, some folks reject the validity of these controlled tests, stating that different mics respond to different positioning in different ways, and their performance in their optimal position is the important issue. I can only suggest that they try some controlled testing in those different positions. After all, if the difference really exists, it should be apparent when levels and positions are matched, right?

And as I expected, some people pointed out that mics with different patterns and mics with very different transducer technology, like ribbon mics, sound different from the cardioid condensers I used. I absolutely agree.

Also as I expected, some people suggested that my use of a single source, the acoustic guitar, is preventing me from hearing the differences, which show themselves on cymbals and vocals. As Dirty Harry was wont to say, “A man’s gotta know his limitations.” I don’t record those sources so I don’t use them for testing .

One comment that has come up a couple of times is that the mics I chose were too similar, all large diaphragm mics from the low end of the spectrum. So I pulled out my highest priced mic, a Schoeps CMC64 small diaphragm condenser, and stuck it in the array.

Variety is the Spice of Mics?

For a little more variety, I replaced the Rode and AT mics with the Shure KSM141 and KSM44. So this set of clips includes two large diaphragm mics and two SD mics, and the price spread ranges from under $200 to over $1500.

I followed the same procedure I illustrated in yesterday’s post, aligning mic diaphragms by eye, playing a test tone through a small speaker about 1 foot from the mics, then adjusting gain on the M-Audio Profire 2626 to match their levels as well as possible in Reaper. Then I recorded the test tone followed by the acoustic guitar clip.

Mics and Clips

So here are the mics:

CAD M179
Schoeps CMC64
Shure KSM44
Shure KSM141

and here are the clips:

download 20090626-F.wav
download 20090626-G.wav
download 20090626-H.wav
download 20090626-I.wav

As before, I’ll post the key to the clip identities in a future blog entry. Or if you post your opinion and preference in a comment here or on one of the forums I visit I’ll email or PM the information to you.

Philosophical Musing

Please let me take a moment to wax philosophical here. No one has reported doing double blind ABX comparisons on the clips so far. Several posters have offered opinions on the sonic qualities of the clips, but no one has confirmed that they can actually hear a difference! This seems to be human nature, but I think that skipping the double blind check is missing a really valuable learning experience.

Figure 8 mics have a pickup pattern that looks like this:

but it’s important to remember that this diagram is a 2D representation of the 3D pattern in space. Basically the pattern looks like two balloons on the front and back grills of the mic, with a null, or area of minimum sensitivity in between.

So for the vocal mic we aim the “balloon” of sensitivity at the singer’s mouth and the plane of minimum sensitivity at the singer’s guitar or uke or mandolin. And we arrange the instrument mic with its diaphragm pointed at the instrument but the plane of the null at the singer’s mouth. It’s more complicated to describe than it is to do.

Here’s a video that demonstrates this technique:


Vocal - Guitar Separation using Figure 8 Mics from Fran Guidry on Vimeo.

Certainly other mic patterns could be used, but no other pattern has a deep a null, and no other is as easy to aim. If you need to record a self-accompanied vocalist, a pair of figure 8 mics, either large diaphragm switchable condensers, or bidirectional ribbons, would be a good investment.

Alan Blumlein

In 1931 Alan Blumlein applied for a patent on what we now call stereo sound. He described techniques for creating the auditory illusion of placement and depth using two (or more) channels of recorded and reproduced sound. As part of this patent application he described an array of two bidirectional mics in a coincident X/Y arrangement that we today call a Blumlein array:

Two bidirectional or figure 8 mics in a coincident XY

In the same document he described the Mid-Side mic arrangement. Rather than a crossed pair of mics at 45 degrees to the source, the Mid-Side array has the Mid mic pointing directly at the source and the Side mic at right angles to the source. The Mid mic can be any pattern but the Side mic must be a bidirectional or figure-8 mic.

Two bidirectional or figure 8 mics in Mid-Side

Mid-Side Recording

This article from emusician.com discusses the technical details of Mid-Side recording in some depth. Note that the use of different patterns for the Mid mic gives different results after decoding.

When I record in Mid-Side using my home recording chain it’s startling to see the difference in the levels of the Mid and Side channels. With both channels set to the same gain the Side channel barely shows any signal.

Decoding the Mid and Side channels to Left and Right is easy in a multitrack recording program. Simply place the Mid channel on one track panned to the center. Place the Side channel on a track panned hard left. Then place a copy of the Side channel inverted in polarity on a track panned hard right. When you mix the three tracks down you’ll have two stereo tracks.

Here’s a video I made demonstrating Mid-Side and Blumlein arrays with some demonstrations of the stereo field.

There are a few ? ? ? problems with the video, please accept my apologies. The bubble wrap stereo demo is funny (to me anyway), but the clipping caused by the amazingly loud pops wrecked the stereo field. Listen to the incidental noises for a better idea of how these recording techniques work. And the distortion is not there in the my recording, it was introduced by the YouTube compression process.

Mid-Side and the H4n

I also missed several opportunities to actually address some details of the H4n. For instance, the level metering shows levels after the signal is decoded. I think there’s a good chance of clipping the Mid mic and not seeing it in the decoded signal.

When setting up the Mid-Side connections on the H4n, notice that there’s a menu selection to identify which channel is the Mid and which is the Side.

Let me wrap up by mentioning that I sent my H4n back to the seller. I think it’s a pretty interesting recorder, but for my regular uses the H2 does at least as good a job. When I want to do more serious recording I just turn on my home studio system. I’m looking forward to continued progress in these handheld recorders, though. I just can’t resist the idea of a world class recording chain in my pocket.

I learned a trick back in my electric guitar days that has really come in handy when I install a pickup in my acoustic guitar and I’ve often thought of sharing it, so today I shot a video of the procedure. My video was totally off the cuff with no script, so I forgot to warn about drilling the end pin jack hole, and I’d like to do that now: most of a pickup installation is easily reversible and/or inconspicuous, but it’s all too easy to do real damage to your guitar when enlarging or drilling the hole through the tail block. It’s not hard or dangerous if you know what you’re doing and you have the right tools but it’s not something to try if you don’t. (Now how would I know that??)

The trick involves using a piece of wire or a guitar string to pull the jack into place. All the jacks I’ve seen have hole drilled through the jack at right angles to the plug, and this little detail is a big help in the installation process. Here’s a picture of the end pin jack showing the main body of the jack, the nut and washer that hold the jack from the outside, and the threaded strap button.

Closeup of an end pin jack showing the handy little hole

The larger threaded section needs to be adjusted so it is very slightly shorter than the depth of the tail block, the block of wood inside the guitar. I bend a sharp right angle in the end of the wire and stick that into the end pin jack hole, let it catch on the tail block and use that to measure the depth.

A simple piece of wire measures the end block

If the length here is too great the outer nut will not apply any pressure to the wood and the jack will spin – this is bad. If the length is too short we won’t be able to get the outer nut tightened – this is bad. I usually expect a couple of adjustments to get it just right.

Here’s a video of the complete process:

Have fun and save a few bucks installing your pickup yourself, but just remember, don’t try to drill out that end pin hole if you don’t know what you’re doing or don’t have the right tools.