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.