I found that installing these panels made a lot more difference in the quality of my recordings than upgrading a preamp or a/d converter, or even buying a new microphone. By improving the sound in the room, the acoustic treatment made the whole recording process much easier and more enjoyable. So when people ask me how to improve their recordings, one of the first things I suggest is room treatment.

Minimum Impact, Maximum Result

Unfortunately many people don’t have a dedicated recording space. They can’t stuff a dozen panels into corners or lean them against walls, and they often ask how few panels they can use and gain any benefit. My standard answer is two, just two panels can reduce reflection in one small area, an area just right for recording acoustic guitar or vocal or many other acoustic sources.

There are a number of commercial products born out of this idea of a zone of controlled reflections. Some of these are rather small and thin, so I’m doubtful that they’re strongly effective. Some are fitted with frames and/or attachment hardware. This adds flexibility and a pro look, but also adds weight and cost. My preference is a pair of simple unframed panels, 2 feet by 4 feet by 4 inches of OC703 compressed fiberglass. I made mine with burlap and hot glue, but premade panels are available as well. Here’s the blog entry on building these panels: Building a broadband absorber (on the cheap)

I deploy the panels in a V surrounding the microphone(s), often by simply leaning them against the mic stand if it’s sturdy enough. If needed I lock the panels in place using a bent coathanger poked into the fiberglass to add a little stability. I’ve experimented with different positions for the panels and this arrangement has seemed the most effective to me. The sound leaving the guitar, or at least a lot of it, passes through the panels as it leaves, so it hits the microphone full strength, then gets attenuated by the panel. Then after the sound hits the wall it returns through the panels for further reduction before hitting the back and sides of the mics.

Let’s Listen

In order to evaluate this two panel approach I set up in our guest bedroom, a 12 x 14 x 8 foot space with no room treatment and only a futon for furniture. This is a fairly reflective room and seemed like a good place to test the two panel solution. I used the Zoom Q3HD as the “mic” and placed it about 24″ from the guitar, with the stick-on wide angle lens attached Zoom Q3HD with a Stick-on Wide Angle Lens then I setup the Xacti HD2000 for a wider shot.

Here’s the resulting video:

Conclusion

I hope you’ll listen and make your own judgment, but my opinion is that the two panels do a remarkable job of cleaning up the early reflections and reducing the “small room” sound. The direct to reflected ratio is improved with a couple of benefits. Since the reflected sound includes a lot of high mids, the sound with the panels is “warmer” with those reflections reduced. The other effect is to make the recording sound like it was made with a closer mic position or in a much larger room.

I’m pleasantly surprised by the effectiveness of this two panel approach. They’re small enough to be stored under a bed or behind a door, they’re light enough that they can be moved into position quickly and easily, and even purchased commercially the cost is under $200. It’s possible that one or two more panels might improve things further, but in my preliminary comparisons it seemed that the big improvement came from two panels, and one or two more panels did not provide much additional benefit. Your situation could certainly be different, of course.

My understanding of microphones and audio says this myth is not true. I’ve been told by knowledgeable experts that mic sensitivity is linear below physical clipping regardless of the transducer technology. I actually asked this question some time ago over on rec.pro.audio – a usenet discussion forum where professional audio engineers hang out. Some of their responses were rude, but they basically established that preamp gain is all that is required to match sensitivity between a dynamic and a condenser mic. Here’s a link to that thread.

Now I believe those guys. I thought it might be interesting to devise a demonstration of sorts, by plugging in a dynamic and condenser mic, playing a reference tone through a speaker in front of the mics, then adjusting preamp gains so the levels match. Then I could generate a quieter and quieter test signal by walking away from the mics making noise. Recording this diminishing sound with both mics would tell me if one could “hear things” the other could not.

Oh No!! Is the Myth True?

To my amazement, when I did conduct a demonstration for myself, I could hear more distant, quieter sounds on the condenser mic. It seemed as if the myth was true.

I knew the error was not the physics or engineering of mics, but rather something I had overlooked in setting up my test. After a day or two of research and pondering the light came on. I realized that the different pickup patterns of the two mics made my calibration procedure wrong. I was calibrating for direct, on-axis sound, but I was measuring diffuse off-axis sound. I needed to do the calibration using only the diffuse sound field, which meant moving the speaker some distance from the mics during the calibration.

A Better Test Design

At this point I also figured out that I didn’t have to move the noise source to reduce the level of the test signal, I could create test tones that got lower and lower in level and play them back from the same spot as the calibration (well, duhhhh).

Here’s the result. For the best fidelity, here’s 45db-66db-xt.wav. Or if your connection is a bit slow, the compressed version is 45db-66db-xt.mp3.

You’ll need to download one of the files and pull it into a player that can select only the right or left channel. The mic in the left channel is the condenser, a Shure KSM141. The mic in the right channel is a dynamic, the Shure SM57. This is a little excerpt from the demonstration recording. I selected the area from -45 to -66 dBFS, which is where the test tone slipped into inaudibility. I raised the level of these files substantially and there is plenty of broadband noise, so be careful not to play them too loudly. The condenser mic is in the left channel, the dynamic in the right. Listen to first one side, then the other, and see if you can hear tones at lower levels from one mic or the other.

Conduct Your Own Demonstration

If you’d like to conduct this demonstration with your own mics and room, all you need is a calibration tone and a test tone series. You can generate the calibration tone in most audio editors, and you can download my test tone series.

If you can’t figure out how to create a tone in your favorite audio workstation software, download Audacity and install it (I recommend the Beta 1.3.xx or later version). Start Audacity and choose

Generate | Tone

then fill out the Tone Generator form:

Waveform: Sine
Frequency (Hz): 1000 (a 1 Khz test tone is the normal industry standard for basic testing)
Amplitude: .6 (a very loud long 1 Khz tone can damage your speakers and possibly your ears)
Duration: 600 seconds (10 minutes should be enough)

Click OK and you’ll see a strange solid waveform. That’s your calibration tone. Just export it from Audacity:

File | Export
Save as type: (either MP3 or WAV Microsoft signed 16 bit PCM)
(Choose a directory and file name)

You can download my test tone file here. The test tone file contains volume level announcements and 1000 Hz tones starting at -9 dBFS and going down to -90 dbFS in 3 dB increments.

Here’s a screen shot of the test tone file:

Mic sensitivity test tone in Adobe Audition 3

and a sample of the tones, starting at -9 dBFS and going to some of the lower level tones:
test_tone_xt.mp3

To conduct your own demonstration, connect two mics to your recording system. Place the mics at least 6 feet from the speaker, then play the calibration tone. Adjust the preamp gain so the two mics show the same input levels. Do this very very carefully, this is the most critical step in the process.

Next, simply play the test tone file while recording the two microphones. You’ll want to wait until a quiet part of the day, and be prepared to sit very quietly while the test file plays. When you’ve completed recording the test tone sequence, listen to one of the tracks you just recorded. When you can no longer hear the test tone, switch to the other track (other mic) and listen again. If your experience is like mine, the test tones will fall into inaudibility at the same level for both mics.

Better Recording By Knowing Our Tools

Mics are fascinating devices, but they’re engineered objects in the physical world. We can make better use of them if we have a better understanding of the way they really work instead of relying on incorrect assumptions and erroneous analogies. In the past audio testing required lots of expensive dedicated equipment, but now with our computer audio systems we can easily perform simple but fairly sophisticated evaluations of our audio gear, and learn to make better recordings in the process.

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.

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.

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 got a long and interesting email from Mark McPherson of Portland, describing his evaluation of the H4n:

Hi Fran,

Mark McPherson here, up in sunny Portland, proud owner of a shiny new Zoom H4N.

I’ve been enjoying your slack-key recordings and gear commentary for some time, and thought I might pass along a few preliminary observations regarding the H4N.

To begin, let me say that I have a modest technical bent. I’m a retired engineering guy, with now-ancient education in engineering physics and math, and an increasingly-ancient career in the semiconductor and electronics industries. Now I dabble in music, and have an ongoing interest in amateur recording, tempered by the fact that I don’t play well enough to make anything worth recording.

I’ve been using an H2 for the past 18 months or so, and have had excellent results with it — there can’t be a better value in small digital recorders. I’ve had particularly rewarding experiences when using it in four-channel mode, mounted on a photographic tripod in the middle of an ensemble jam. I had an H4 for a short period, but returned it after finding lots of wide-spectrum noise in the preamps, the infamous beep problem, and various whistles and descending and ascending tones in recordings made with external mics with phantom power applied. And I hated the user interface passionately.

I think Samson/Zoom fixed some of this with the H2. Much better user interface, decent mics, simultaneous four-channel recordings, simple yet useful software to pan, mix and normalize the four-channel recordings in the recorder — wonderful stuff for the price.

So I was mighty hopeful when I saw word of the impending release of the H4n, thinking that the light had been seen at Zoom, and the H4′s defects perhaps laid to rest.

I’ve had my new H4n for a week now, and have found a few things that might be of interest.

Overall, I’m hugely impressed with improvements in the mechanical design, build quality, and can live with the user interface, which is better, but far, far from intuitive. I’d appreciate better display resolution, but it’s bigger, brighter, and it works well enough. I really like the use of more durable metal 1/8″ jacks for frequently-used I/O ports.

I’m anxious to learn where the single gain control for the preamps is placed in the input circuitry. I haven’t yet tried to determine this. The onboard microphones seem adequate, if perhaps a trifle bright for my taste.

Last night I decided to check on the phantom power situation, having read a post or two on the Nature Recordist’ site about problems. My only mics requiring phantom power are a pair of MXL 604s, Chinese small-condenser devices. Nothing particularly special about them, and certainly not low-noise.

After attaching them to the recorder I turned on 48V phantom power and made a 2-channel recording. I heard a fair amount of hiss, and the old familiar ascending and descending “whistle” tones at low levels, too, and was quite discouraged. Adding or removing the AC power adaptor made little difference. No “beep”, though.

Then I decided to set up the recorder with a 16 GB Transcend HDSC card, put it in four-track mode, and let it run overnight on AC power to see how the recorder handled the transitions at the 2 GB file size limit, and also what happened when the card filled up. I left a pair of half-discharged NiMH batteries in the recorder, set the record gain to “50″ for all mics, and let it run over night.

I’m happy to report that the recorder with 16 GB Transcend HDSC card installed ran smoothly all night long, making several sets of files smoothly and apparently seamlessly, and that the final file terminated properly when the card filled up. The recorder seems to handle that 16 GB card without problems. I think I’ll order another one.

Another interesting thing was that, after about ten minutes of recording, much of the unwanted whistling and noise I associated with the phantom-powered external mics disappeared and did not return. These mics are not used frequently, so there may be some interaction between the Zoom’s phantom power supply and some temporary mic behavior which disappeared with use. Anyway, the message here might be that if you encounter noise, particularly ‘whistles’ of ascending or descending frequency on the H4n’s external inputs with phantom power applied, it may make sense to let a recording run for an hour or two and then re-examine the noise profile.

It also appears that the NiMH batteries in the Zoom received a charge while the AC power adapter was in use overnight — they were pretty flat when the recording started, but by the next morning were apparently fully charged again. Not sure I saw anything about this in the manual, but I may have missed it. Nice if true.

So I’ve gone from thinking the H4n to be no better than the H4 at recording to thinking that it may just fill the bill for a decent four-channel-capable machine, without high expectations for low-sound-pressure recordings because of the preamp noise, which appears to be a little better, but not exactly transformed. I’ll repeat some of this stuff to validate it, but right now I’m pretty happy, and thinking this is a good value and can be a useful tool. I considered purchasing the Sony PCM-D50, but really wanted the four-channel recording option and like having the ability to plug in a couple of mics requiring phantom power.

Hope this is of some interest, and would be happy to share any other data or try some simple tests with the gear I have here if it’s useful to the cause…

Cheers,
Mark McPherson

In further discussions with Mark we’re questioning whether the odd noises he heard were in fact coming from his microphones rather than the recorder. We’re both talking about ways to do more rigorous testing.

In the meantime I’ve been exploring the Mid-Side recording feature of the H4n, and I hope to have a post about that soon.

Zoom Field Recorders

I’ve had a Zoom H2 field recorder since they were delivered and it has been a very satisfactory tool. I’ve used it to capture audio for my YouTube videos, to record hula accompaniment for my wife, to archive band rehearsals, and to save ideas for original compositions. A very satisfactory tool, but not quite CD quality, not quite the tool I would use for high quality recording. The self-noise just peeks into the quiet spots and long fades, the mics roll off a bit above 16 Khz.

I have posted some comparison tests between the H2 and other recording chains here on Home Brewed Music: a comparison with my best studio recording chain and a shootout with several other field recorders. In both cases the H2 was “amazing for the price” but not the winner.

The H4 preceded the H2, cost a bit more, does multi-track recording and has XLR inputs and 48V phantom power for serious microphones. There have been many complaints about the user interface and the fragile feel of the controls. I’ve never used one myself, so I can’t say anything about the recording quality.

Both these units offer a remarkable level of functionality, with multitracking on the H4 and surround sound on the H2, and both function as a USB interface for recording directly on the computer.

What’s new with the H4n?

This year Samson/Zoom announced a new recorder, the H4n. This unit has a larger LCD screen, improved user interface, and according to the manufacturer, improved mic preamps. I ordered one as soon as they were available and it arrived today.

The H4n is only slightly larger than the H2, but it is just that bit too big to be comfortable in a shirt or pants pocket. And the mics sticking out without protection also make it unlikely as a pocket device.

The bright orange LCD screen on the H4n is a big improvement over the H2 and H4. The look and feel is also more impressive, with a style and solidity that are missing from the earlier units.

The gain setting on the H4n is a big change from the H4 and H2. Both those recorders have a 3 position level switch, which sets the preamp level before the a/d converters. Then another control sets the recording level from 1-100, but this setting is applied after the a/d converter and mic preamp. This means that only the 3 position switch can actually lower the recording level in a way that prevents overload and distortion, and the second finer control is essentially useless.

The H4n has only the incremental gain control from 1-100. Hopefully it is implemented so that it turns down preamp gain and controls overload. I’m counting on the smart guys at the Zoom H2/H4/H4n forum to poke around and figure out the details.

I was expecting features like auto-level, limiting, and auto-record, but Samson/Zoom surprised me by including a Mid/Side decoding function in the preamp as well.

Recording with the H4n

Well, how about some clips? The big bright screen on the H4n makes level setting easier than the H2, and with my recording mode all set to stereo 44.1/24, recording is just as easy as the H2 – one press of Record starts standby mode for level checks, then one more press and we’re storing bits.

After a quick recording a feature I never thought much about – a monitor speaker – turns out to be very comforting. Just hit play and there’s confirmation that you captured something. Its time to move the tracks to the computer, and this would be good time to compliment Samson/Zoom on their manual. This little recorder has a ton of features and the manual has covered every one I’ve needed so far. Page 35 clearly explains how to connect the H4n to the computer over the USB connection and it worked like a charm on my XP SP3 system.

Another improvement is obvious and very welcome – this new unit is a USB 2.0 High Speed device. The previous H4 and H2 are both USB 2 compatible, but they are anything but high speed. This H4n makes my standalone cardreader obsolete. Switching cards in and out draws attention to a potential problem, though. The door over the SD card slot does not look rugged enough for the use it will get. I kind of expect to see a lot of these with masking tape or gaffers tape covering the SD slot when they get older.

Hey, as long as it’s hooked to the computer, let’s see how it works as an audio interface. Maybe I’m just having a good night, but everything goes smoothly, Adobe Audition 1.5 sees the Zoom H4n and records a decent track.

Here’s a little “Opihi Moemoe” using the H4n as an audio interface, using the built-in mics. The positioning is about 30″ between the guitar and mics:

opihi.mp3
or download opihi.mp3

Sounds pretty good to me, but in the fade at the end you can hear a bit of noise. Hmmmm.

A four way comparison

The main comparison is between the two Zooms, the Fostex FR2-LE, and my main studio recording chain, a John Hardy M-1 preamp feeding a LynxTwo-C A/D converter. A pair of Shure KSM141 mics provide audio to the Fostex and John Hardy. I tried to group all four units as close as possible.

Two mics and two Zoom recorders

Each of the clips is mono, I kept only the Zoom track from the mic that was pointed toward the guitar. The streaming clips are MP3, but the download is a PCM WAV file and considerably larger. I positioned the guitar 3 feet from the mics. This is a quite a strenuous test of the recording chain, because the guitar is such a quiet instrument that plenty of gain is required even for much lesser distances.

The Fostex:
1-1-FR2.mp3
or download 1-1-fr2.wav

The H2:
1-2-h2.mp3
or download 1-2-h2.wav

The H4n:
1-3-h4n.mp3
or download 1-3-h4n.wav

The Hardy:
1-4-jh.mp3
or download 1-4-jh.wav

I’m a bit disappointed with the results here. I was hoping the H4n’s new preamp and mics would provide a big improvement in noise performance compared to the H2, but I’m not hearing it. Listening to the long fade at the end of the clip, both the Zoom units exhibit more noise than the other two systems. Of course this is an extreme test, and with a more normal recording distance the noise wouldn’t be a problem. And the source of the noise might be the mics rather than the preamps, so it’s only fair to compare the H4n with one of the Shure KSM141 mics.

Using external mics

The Fostex with Shure mic:
2-1-FR.mp3
or download 2-1-FR2.wav

The H4n with Shure mic:
2-2-h4n.mp3
or download 2-2-h4n.wav

In these clips the guitar is a little closer to the mics, about 30 inches. This is still far enough to require a lot of gain, and both units exhibit some noise. But again the H4n is a touch noisier than the Fostex in the fade at the end of the clip. With the external mic, though, the difference is a lot smaller.

In the four way comparison, the studio chain with the Hardy preamp and Lynx converters was clearly the quietest. How does the H4n do in a head to head with the champ?

The H4n with Shure mic:
3-1-h4n.mp3
or download 3-1-h4n.wav

The Hardy with Shure mic:
3-2-jh.mp3
or download 3-2-jh.wav

This recording has the guitar even closer, less than 2 feet and just far enough to avoid proximity effect. With lower gain and the external mic the H4n sounds a lot less noisy but still just a hair more than the Hardy and Lynx.

And so the story is told

I’m really quite impressed with the H4n. It has a solid feel and a look that inspires confidence. The controls work cleanly and seem sturdy. The large bright display makes the unit much more friendly to old fogey eyes like mine. The manual is substantial because the feature set is pretty amazing. I’ll probably only scratch the surface, but plenty of other musicians will find use for the multi-track recorder with overdubbing, effects, metronome and so on. Folks doing interviews and recording lectures can benefit from the limiter, automatic gain control, and auto-record.

How is the H4n as a solo acoustic guitar recording tool? I’d say about 95%. The tonal balance of the recordings are fine, the dynamics are good. I’m quite happy with how the guitar sounds with either the external mic or the built-ins. I’m a little bit disappointed by the noise performance, though. A bit closer placement, a little noise reduction software in post, it’s a problem that can be solved, but I was hoping for world class performance from this little unit and I’m afraid it’s not quite at that level.