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.

Sometimes when I’ve listened to mic samples I thought I heard these dramatic differences, but after a bit I realized that I was listening to different performances, not different mics. Sure the mics had been changed, but the player was hitting the strings differently and playing different riffs at a different volume – so how could I tell what part of the difference was the mic, and what part the player?

Since then I’ve tried to do some mic tests of my own, and I’ve tried to educate myself on audio testing. At this point I’m beginning to think that the differences in microphones are a lot more subtle than I had been led to believe, which makes a careful test even more important. As I’ve mentioned before, very small differences in volume are registered by our ear/brain combination as differences in quality rather than loudness. I’d like to demonstrate the steps I now take to try to make my mic comparisons, and preamp and a/d comparisons, meaningful.

Mic Setup

The mics need to be close together, but not interfere with each other. I try to determine the location of the diaphragm, the part of the microphone that gets hit by the sound waves, on each mic, and align them along that position. This is pretty easy with large diaphragm mics, often a bit tricky with small diaphragm units. All the mics should be on axis to the source or all should be equally off axis. Check pattern switches, rolloff settings, pads, any feature of the mic than changes its response. I’ve missed this step a few times.

I also arrange the mics so they don’t interfere with each other. For instance, it’s not a good idea to tie a bunch of small diaphragm mics into a bundle, because the ports behind the capsule contribute toi the frequency response and pattern of the mic. If those ports are blocked the mic is not performing normally.

There are three mics being compared in this example. The CAD M179 is a low cost continuously variable mic in an unusual looking housing. One salesperson began a drumbeat for these mics and they are now widely recommended in internet recording forums. The Rode NT2a is one I’ve used before. I think it does a fine job of capturing audio with low noise and no noticeable distortion, but many forum posts are negative toward Rode in general and the NT2a in particular. The Audio-Technica AT3035 has recently been discontinued, replaced by the AT2035. In the past I’ve read a wide range of comments about this mic, with some calling it a secret gem and others decrying its overwhelmingly bright character.

Here’s a picture of a mic array arranged for testing. A cheater clamp that fastens to the mic stand main tube can help fit an extra mic into the array. Adapters to attach mics at an angle can be very handy as well.

Three large diaphragm mics in an array for comparison

I often hear this arrangement, with all the mics equidistant from the source, criticized because different mics work best in different positions. I strongly suggest that if you wish to evaluate different positions you try all the mics in all the positions. It’s a little more trouble, but it’s a great learning opportunity, and omitting this step means no valid comparison can be made. We’re right back to asking what part of the difference is the mic, what part is the location with no way to answer the question.

Of course, my aim here is different from trying mics and positions to get a good recorded sound. I’m after data, not art. When the aim is art, the ears rule!

Equipment wise, you can do a useful comparison with as few as two recording inputs. In fact, comparisons that are done two by two are probably the most revealing and useful. Still its fun to line up three or four mics for a single session – in which case it’s helpful to have four identical channels, especially if the comparison will be made public. In my experience, more posters will criticize a change in preamp than will mention a change in performance, amazingly enough.

Here’s a video that illustrates the setup process and takes you through gain calibration, discussed below:

Microphone Comparison - A Tutorial - part 1 of 2 from Fran Guidry on Vimeo.

Gain Calibration

Once we’ve arranged the mics to capture a single performance we need to minimize the volume difference in the our samples. I like to start with a test tone played into all the mics from a speaker only a foot or so away. A 1000 Hz tone is not very challenging, so even a low cost computer speaker can be used as the source. A test tone is easy to come by and it doesn’t need to be calibrated for volume since we’re interested in relative rather than absolute levels.

I’m using Reaper to conduct this test, and a little inquiry on the Reaper user forum and learned about MDA Test Tone, a plugin that provides the beep.

In Reaper I created a project with MDA Test Tone on one track, and three tracks for recording the three mics. I also adjusted the range of the Reaper console meters. With these connections in place I hit record and adjusted the preamp gain for each mic so they all were very close to -18 DbFS.

Next I discarded these recordings and captured three more tracks to store a consistent level for each mic. These 1000 Hz tones are used to fine tune the track levels later.

Recording

In the next video we actually do a little recording. After all the setup and calibration work, the recording process is anticlimactic. Move the calibration speaker, tune up the guitar, hit Record in Reaper, play a few bars, and we have our clips in the can. Be sure to record the clips on the same tracks as the reference tones we created in the last step. That way when we adjust the reference tones we adjust the clips at the same time.

For straight mic comparisons, I like to position the guitar about 32″ from the mics. This avoids proximity effect and hopefully presents a fully developed guitar sound to the mics, instead of one mic picking up the neck of the guitar while another picks up the bridge.

Here’s the video demonstration of recording simultaneous tracks and fine tuning the gain:

Microphone Comparison - A Tutorial - part 2 of 2 from Fran Guidry on Vimeo.

Volume Fine Tuning and Rendering

As the video illustrates, working with that 1000 Hz test tone can be pretty annoying, but we need to delve into it one more time. Actually, this time we can turn the volume down, because we’re adjusting levels “in the box” – that is, internally in the computer.

The helpful folks at the Reaper Forum pointed me to the Sonalksis FreeG plugin. This tool adds high resolution metering and gain adjustment we can use to tweak the levels of our clips that last little bit.

Simply place the Reaper track cursor so the recorded test tone will be played, reset the FreeG meter, and play a bit of the clip (the space bar starts and starts playback). Note the RMS level, and repeat for each track. Then, to be fair, apply a gain adjustment to each track so they all show the same RMS level. In the video I’m fiddling with the Gain knob using the mouse, but after I recorded the session I realized that you can simply type the desired gain change into the value box, making it very easy to get the level just right.

Finally, click and drag the cursor to make a time selection of the recorded clips, then render each track separately as illustrated in the video. It’s a good idea to render to 44.1/16 format if you plan to make the clips public, because everyone can play this CD standard format.

Blind Comparison

I have had the experience many times of listening to mic comparison clips and clearly hearing the difference between them when I knew their identities, then finding that I could not hear a difference at all when I hid the identification in some way. Even getting momentarily confused about the source of the clips has been enough to change what I “hear”. Our brains are at least as important as our ears in defining what we hear, and our brains like new stuff, shiny stuff, expensive stuff. So when we know a clip was made with our shiny new expensive mic, we’re going to “hear” how wonderful it sounds.

For a test to be meaningful, we need to hide the identity of the clips somehow. This is pretty hard to do when working by ourselves. The foobar2000 audio player offers one solution, with the ABX testing utility built-in, as described in this blog post. This is a powerful tool, because it not only offers a way to test clips double blind, it helps us determine if we can hear any difference at all before we try to determine a preference.

Mic comparisons are useful for our own recording knowledge, but it’s even better to share. There are lots of folks hanging out at recording forums on the internet who are looking for information about mics and other recording gear. I like to contribute when I can by posting comparison clips, but I think it’s important to make the original post without identifying the devices used. It’s more informative, and more fun too.

So here are the three clips I recorded in the video, with no EQ, no compression, no reverb, no processing of any kind except to match volume levels and trim ends. To recap, the three mics being compared are the CAD M179, Rode NT2a, and Audio-Technica AT3035. Naturally the clips are not in the order listed.

download 20090625-J.wav
download 20090625-K.wav
download 20090625-L.wav

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.

I (naively) expected that people would embrace an opportunity to do some controlled testing, using an easy but very effective comparison technique. I have found that careful ABX testing, using Foobar2000 and the ABX utility included in the program, has made me a better, more careful listener. I learned that the perceived differences between clips became much less when I no longer knew the source of the clip. As a result, I learned to search out subtle differences in tone color and texture. I also learned that I can’t hear any difference between systems that I have been told should show night and day differences.

I’d hoped that a number of other folks would try careful ABX testing of these clips with a statistically significant number of trials, so I could compare my results to theirs. At this point, I don’t know if my inability to hear the differences is normal or unusual.

The Question

If you visited here, listened to the clips, maybe even downloaded and installed Foobar2000, why did you not go the next step and run a test of 20 comparisons? Foobar2000 makes it easy to save your results and share them with the world, or not. Wouldn’t you like to have a personal evaluation of the difference between a high end preamp and a commodity unit, or between 44.1 and 192 sampling rates? Wouldn’t you like to contribute to the knowledge of the recording community?

After all, if the huge differences we read about in magazines and online are true, it will be easy to pick out the different samples, and we can get busy saving up for high end equipment. But if those differences are actually imaginary, driven by normal human traits like confirmation bias, we can save a bunch of money and time and trouble by ignoring gear lust and concentrating on mic placement and room acoustics.

So the question is, what do you have to lose by conducting a thorough series of ABX comparisons and reporting the results?

The Answers

Here are the sources for the clips from the last post:

090420Test1A.wav – Lynx & Hardy
090420Test1B.wav – Profire 2626

090420Test2A.wav – Profire 2626
090420Test2B.wav – Lynx & Hardy

090420Test3A.wav – Lynx 192
090420Test3B.wav – Profire 44.1

I hope these clips provided some useful information for you. They certainly helped me feel confident that I can make recordings with the Profire 2626 that will fully measure up to those made with the LynxTwo.

Since my interest in recording began only a few years ago, I’ve always had the internet as a resource for learning about the subject, I researched in every forum and magazine site I could find. And I now firmly believe that most of what I learned there was incorrect.

I should have been on my guard, because years ago in my pursuit of the playback side of audio I learned that uncontrolled listening tests are simply delusion at work, and that people routinely hear remarkable differences where there are none at all. But when I started trying to learn to record I was persuaded that different preamps and different a/d converters would make a night-and-day difference in my recordings. So I upgraded, then I upgraded again. When I started doing careful comparative listening, I realized that I wasn’t hearing these predicted major differences. In fact, I wasn’t hearing any difference at all.

Controlled Listening Tests

Since then I’ve tried to set up carefully controlled tests to compare gear. It’s not easy, at least for me. I seem to often miss some important detail in the setup, creating differences that shouldn’t be there. When I tried to compare three mic preamps I had the high pass filter (a low cut switch, in other words) active on one preamp. And when I tried to compare several field recorders, one recorder was set to record mp3s instead of waves, and once again the high pass filter was on. But I keep trying, and I’m getting a little better, I think.

ABX and foobar2000

ABX testing is a well established method for comparing two audio files (or other sources). A proper ABX test has only two items under test. The listener can take as long as they want, listen to either clip as many times as they want, go back and forth from the unknown X to the known A or B as often as they want. Then they state whether X is A or B. Not which they prefer, but simply which is which. Then the test is repeated for enough trials to achieve statistical validity.

ABX was originally hardware based, complicated, and expensive. But if we limit our testing to existing audio files we can do ABX testing in software. Various programs that implement ABX testing of digital audio files has been around for a number of years. The orginal PCABX.COM site has been allowed to lapse, but some of the introductory material is still available here.

I found a nifty program that makes the ABX process technically very easy. foobar2000 is a terrific freeware audio player that includes an ABX utility.

A New Audio Interface

I’ve been happy with my LynxTwo-C audio interface for a number of years. It has worked reliably, Lynx Studio has kept the drivers up to date and solid. But I’ve done a couple of sessions lately that could have used more inputs and more mic pres. The Lynx card offers some high powered expansion options, but I was also looking for a system that would integrate my monitor and headphone outs. I’ve been using a system that can only be called a kludge, although a successful one.

Meanwhile, the word on the M-Audio Profire 2626 has been good, I found a B-stock unit on Ebay and bought it. I began by installing the Profire on a nearby computer, leaving the Lynx card in my audio system. And with both systems installed, it was clearly time to try to do some carefully controlled listening tests.

Dynamic Mic, Two Preamps, Two A/Ds

Small variations in volume can apparently be recognized, but the listener hears a quality difference rather than a volume difference. Richard Clark has conducted hundreds of blind tests of amplifiers and says that he adjusts volume to .01db accuracy, although most people can’t detect differences of .1db.

In my first test of two preamps into two different converters, in an effort to create files of equal volume, I started each file with a test tone, generated from Adobe Audition and played through the LynxTwo output. I adjusted the John Hardy M-1 and the Profire input gain to create a signal at -18db, measured by eye on each system software mixer. Then I left that gain setting for the musical recording. I had planned to make the final precise adjustment to the gain in Adobe Audition, but to my surprise the software was precise only to .1db. So in spite of my efforts, the samples are at slightly different levels.

In this test I used a dynamic mic, an Electrovoice RE15 connected through a Coleman Audio LS3, basically just a y-connector, to the two preamps. I recorded my solo acoustic guitar about 2 feet (.6 meters) from the mic. This resulted in a very low signal and a tough test for the Profire preamp.

Here are a couple of clips that are easy to tell apart. I had hoped that the preamps on the M-Audio Profire 2626 would replace my faithful John Hardy M-1, but if you listen to the end of these clips you’ll hear a lot more noise in one clip – that’s the Profire.

download 090420Test1A.wav
download 090420Test1B.wav

But what if we trim off the end of the clip. Can you still tell the two recording chains apart?

download 090420Test2A.wav
download 090420Test2B.wav

Condenser Mic, One Preamp, Two A/Ds

I’ve seen quite a few debates about the audibility of a/d converters. Many people posting on the internet state as fact that prosumer level converters can’t compare with high end devices. And many prefer the sound of recordings made at high sample rates, insisting that they sound better even after conversion to the CD standard 44.1/16 format.

This time I used a Rode NT2a into the the John Hardy M-1, then the Coleman LS3 to split the signal to the line inputs of the LynxTwo and Profire 2626. Even with both units at nominal line level (+4dbu) there were small volume differences. Surprisingly, the unit with the longer cable run was louder. So once again we have slightly different volume levels that may make our ABX testing less valid.

download 090420Test3A.wav
download 090420Test3B.wav

How To ABX

Start by ownloading the clips above. Save them in a place you can find, like your music folder or your desktop. Maybe create a folder for this project.

Then you’ll need to download and install foobar2000. When you are prompted for the kind of install, choose Full.

When installing foobar2000, select the Full option

Start foobar2000 and open a pair of the test clips. The clips are named Test1A and Test1B, etc. Select both clips, right click, choose the Utils menu item, and there you’ll find ABX. Here’s a video that demonstrates the use of foobar2000 and its ABX comparator:


ABX Audio Testing with foobar2000 from Fran Guidry on Vimeo.

I hope some of you will download these samples and foobar2000 and conduct your own test. I’d be interested to hear the results of any ABX tests you conduct. Please contact me through the comments section with your results. I’ll post the keys to the samples in a future update. Let’s say, 2 weeks after this entry. (Mean, huh?)

I also hope you’ll make your own controlled comparisons and do your own ABX testing of preamps, converters, DAWs, cables, and other odds and ends of audio gear. Perhaps we can all learn something.

But for this occasion, I went to take advantage of his extremely cool Sound Devices 744 digital recorder. This is a top of the line system, used widely for major motion pictures or any other situation where great sonics, ruggedness, and portability are needed. I came for a shootout between his “king of the hill” unit and my much more modest recorders, a Fostex FR2-LE and a Zoom H2. Once I arrived, Doug suggested that we add his Edirol R09 to the mix, so we had four field recorders to compare.

I brought along my Wingert Model E tuned to G Wahine (D G D F# B D), a great old slack key tuning. Doug kindly hooked up his Schoeps CMC 6 mic bodies with his MK41 supercardioid capsules, one into his Sound Devices, and one into the Fostex. Then we rigged the Zoom and Edirol on stands to bring them close to the same position. Here’s what the setup looked like:

and here’s a shot from over the mics and recorders:

The Schoeps are directly over one another, so the bottom one disappears in this overhead shot.

In some rooms, this setup might not be tight enough to give an accurate comparison, but Doug’s studio is very well treated with broad band absorbers, so the sound is clean and even in most locations. Doug’s room is also extremely quiet, so we got some nice long “tails” as the last note of the clip died away. This will give you a chance to compare the internal noise levels of the different recording chains. One embarrassing caveat – we left the Edirol R09 in MP3 mode instead of 44.1 wave, so that little guy may be suffering some quality degradation. We didn’t realize our error until we’d used up all our time for the evening. Apologies to Edirol and R09 fans.

After the recording session, I brought the clips into my Adobe Audition 3.0 where I trimmed them as accurately as I could to the same starting point and length. (Once again I forgot to “clap” the start of each clip to get a synchronization point – the learning never ends.) I converted the H2 and R09 clips to mono by using the louder of their two tracks. Then I used AA3’s group normalize feature to bring them to the same average loudness. Loudness differences have a tremendous impact on the listener’s sonic evaluation, so I wanted to level the playing field in that aspect. I think average perceived loudness is more useful than peak normalization in this situation, and after processing I listened to the samples on my Dynaudio BM 6 monitors and thought their levels were extremely close.

Now for the samples. Just for fun I’ll post them blind, so you can download them and compare without prejudging. These are .wav files and fairly large, but we wanted to preserve the fidelity so you can make a better comparison.

Sample 1
Sample 2
Sample 3
Sample 4

Now after giving a good listen to these clips, you can see the key here and evaluate the results. I hope you find these comparisons useful, and that you’ll leave a comment or send an email sharing your impressions.

As always thanks a ton to Doug for being so generous with his time, space, and gear.

I bought mine slightly used on Ebay. I saved a few bucks but even at the street price of $199 this is a pretty easy purchase to scrape up. Taking the thing out of the box, it’s pretty unimpressive – light and flimsy rather than solid and sturdy. The membrane switches gave me fits until I figure out that I should use my big fat finger instead of a delicate little touch with my fingernail.

Naturally I have to do a comparison test between this little recorder and the PC rig. Here’s a picture of the setup I used:

The mics are a pair of Schoeps CMC6 bodies with MK41 caps, in a pretty careful 90 degree X/Y. The Zoom is as close to the same location as possible, using the front mics in 90 degree configuration.

I recorded my Martin OM-18GE in drop C, doing a chorus of “Silver Threads Among the Gold.” I’m posting the recordings without trying to encourage a blind test. I posted .wav files instead of mp3s, so the downloads will be a bit long, but you can do a careful comparison.

Schoeps

Zoom H2

I think anyone can hear a difference between these two samples, and I certainly prefer the Schoeps track, but if you add up the cost of duplicating the Schoeps->John Hardy->LynxTwo chain and compare it to the cost of the Zoom, well, that Zoom doesn’t sound too bad after all.

I also tested the H2 as a PC interface. The supplied USB cable and power adapter, along with the silly looking little plastic tripod stand, had me ready for some kitchen table recording in no time. One down side to this use, I have to go into the menu and setup the USB link every time I turn the H2 on. Not a big deal, but I wouldn’t mind if the unit could remember where I left off.

I don’t have any samples of this use of the H2, because I got wrapped up in doing multi-track experiments in Audacity and Reaper, but I haven’t come up with anything I am willing to make public yet. But I can say that the H2 works as a stereo USB mic with no hassle beyond the menu tweaking.

I’ve held on to my old minidisk recorder for a number of years, but it looks like I don’t need it anymore. This new recorder is going to get a lot of use around here.

Now I know that preamps are used as effects, either blatant or subtle. The blatant ones are inexpensive units with a starved plate tube glowing prominently through some grillwork and a “drive” control to mix distortion generated by this tube into the signal. The more subtle ones often refer to various recording consoles as their inspiration, claiming Neve-like or API-ish qualities. I’ve never experimented with units like these. There may be huge differences between preamps when they’re used on vocals, drumsets, electric guitar amps, or exotic percussion, I just wouldn’t know. My focus is always on simple solo fingerpicked acoustic guitar recordings, where accuracy and clarity are my goal.

Many preamps aim to be accurate. The classic description of an accurate preamp is “a straight wire with gain,” an impossible achievement but an easy ideal to visualize. Product literature and user comments include terms like detailed, musical, natural, transparent. Inferior versions of these accurate preamps are described in internet forums as flat, boring, or two dimensional. Since I have a few preamps around these days I decided to try to do some comparison tests. As always with comparisons like this, the source material is a key issue. I decided to try to run one microphone through all three preamps at once, so the input signals would be the same. Making this connection is fraught with problems. If I connect the mic directly to the three inputs, the input impedance seen by the mic will be quite low, and may affect the mic response. If I use a transformer splitter or active buffer/splitter, the sonic signature of the splitter will be stamped on all the samples. My decision was easy, though, because I already have a box that lets me rig up a passive connection direct to the three inputs. If the mic response is affected, I’ll assume (until I’m shown otherwise) that the response is still the same for each preamp.

The key to this setup is a Coleman Audio LS3 switch box. I normally use this box to select between my headphone amp and monitor amp, but since it’s a completely passive box it works to route inputs or outputs equally well.

The three preamps under evaluation are the John Hardy M-1 as mentioned earlier, along with an FMR RNP and an M-Audio DMP3.

For the first test, I selected an Audio Technica AT4041 small diameter condenser mic. I routed it through the Coleman LS3 to the left channel of each preamp, then connected the left output of each preamp to an input of my LynxTwo C. I matched the volumes rather roughly using pink noise generated by Adobe Audition 1.5 and the metering on the Lynx software mixer. I set up a multitrack session in AA 1.5 to record three mono tracks from the three preamps. I positioned the AT4041 about 12″ from the 12th fret of an Epiphone Masterbilt EF-500M tuned to “drop C” tuning – CGDGBD low to high, and played a brief bit of noodling. After I listened to the tracks I realized I had not matched the levels well enough, so I normalized all the tracks to -3db. Here are the three sample tracks, mono 44.1/16 wave files:

Sample 1
Sample 2
Sample 3

Finally, I thought I would include a comparison with a dynamic mic as the source. It would require more gain from the preamps, and might be useful to folks who only have handheld dynamic stage mics in their collection. This time I used an Electrovoice RE16, connected as before. Again I set levels using pink noise and the Lynx software mixer, then recorded in a multitrack AA 1.5 session. This time the level matching was more accurate, so I didn’t feel the need to adjust the levels after recording. Naturally the performance is different from the first recording, AND THE ORDER OF PREAMPS IS DIFFERENT:

Sample 4
Sample 5
Sample 6

I hope you’ll download these and give a listen. Does one track in each set stand out from the others? Is one more transparent, another lifeless? Can you tell them apart? Perhaps you’d like to know which sample was created by which preamp? Click here for the key to relate the samples to the preamps used to create them.

PS – After I posted these, and after I sold my FMR RNP, people pointed out that the DMP3 samples were high-passed – that is, the DMP3 LoCut switch was activated, causing a shelving rolloff -3db at 72hz, 18db per octave. This may affect the comparison for some listeners and some playback systems.