I decided to do a test of digital recording on two wildly different sound cards. It was interesting for a number of reasons:

• demonstrates the technique of double-micing a guitar amplifier
• proves that you can actually see the speed of sound in your own studio
• proved the importance of a good user interface in a digital sound program
• shows the difference in results between two microphones: a dynamic and small condenser type
• shows the difference in quality between a $30 sound card and a $600 sound card

Got you hooked, huh? Good! 'Cause this took a while to do!

Methodology

I used my computer-based audio workstation, which has two sound cards in it. One is an AARK 20/20, a high-end card with breakout box and 8 analog ins and outs. The other is a Yamaha PCI card that came free with my new computer, and has model numbers like Y724 and DS-XG on it, if that helps any. This one has MIDI I/O through the joystick port, and a pretty good wavetable synthesizer.

I hooked up two mics. One was a Shure SM-57 dynamic, which was positioned at an angle to the guitar amp speaker at a distance of maybe 6" (15 centipedes, in the slightly buggy metric system :-). The other was an AKG C1000S condenser, which I put on a mic stand about 9' (3 meters) away and about 3' (1 meter) in the air, pointing at the amp. AKG on the left, Shure on the right, so you can listen to them separately as well as together.

Because the AKG needs phantom power, I ran both mics through the mixer section of a TASCAM 488 MkII, and ran the output of that into each sound card in turn. I did the actual recording in Sound Forge XP (at 44.1 Khz stereo, of course), where I was able to easily adjust for DC offset (none on the AARK, tons of it on the Yamaha), normalize to -0.5 dB, and save as a stereo WAV file.

Maverick Goes Supersonic

It's a well-known fact that you can run into phase problems when using two mics at different distances. Normally, setting things up requires lots of careful work, moving mics around, listening in headphones, and so on. Well, just try that when you're playing too! It's a pain, and I like cutting corners if they don't adversely affect quality. Anyway, since sound travels at about 1100' per second, you can easily see that there's about a 1 millisecond delay for every foot of distance between the sound source and the microphone.

I had read about a cool technique for fixing this, which I'm now going to lay on you. When you record using this 2-mic technique, you stick a 10 ms. delay in series with the close-up mic (which you can do with a channel insert) so that it will "arrive" at the same time as the sound from the farther-away mic. Bingo: no more phase problems.

Well, that's an antiquated analog way of doing things. :-) So what I did when I was all done playing was I said to myself, "All I have to do is slide one track down in a digital editor until it lines up with the other one!"

I thought it was pretty clever, anyway. But I didn't find any easy or obvious way to do this in Sound Forge XP...or Cool Edit 96...or WaveFlow...or Power Tracks Pro Audio...or any of the other special-purpose digital audio editors I've collected over the years. Heck, I even looked in their help files!

I do have Cakewalk 8, so all I had to do was open up a new project, insert the WAV file, select both tracks, click once to bring up the audio view, zoom in till I could see the waveform of an obvious point on both tracks (the beginning of a chord), click on one of the tracks, grab it with the mouse, and slide it to the left until it matched the other one. The whole process took about 90 seconds.

The distance I had to slide it was due to the speed of sound! Q.E.D.

Then I exported to another WAV file and converted to 128 kbps MP3. I deliberately left in some silences, so you can listen for sound card noise, but any hum you hear is probably from my Fender tube amp. Each cut starts off with a second or two of digital silence, so you can hear what real silence sounds like.

By the way, the entire reason that I had to play the guitar for this is not because I wanted to show off my guitar playing (you'll know that when you hear it :-). I would have much rather used some program material familiar to all, but there's this little problem of copyright laws...so I couldn't even play you one of my (in)famous cover tunes. I just kind of whanged away on the guitar.

If I get enough complaints about the fact that I used distortion on this and you really want to hear vocals or acoustic guitar, I might be able to come up with something. But I'm even more shy in those departments, so for a while at least, you'll just have to be content with this.
-- Dragon

AARK recording (MP3)
Yamaha recording (MP3)

P.S. If you can't hear the difference, turn it up a bit. The actual noise floor of the Yamaha card was probably something like 30 dB or so, whereas the AARK...didn't have any. But the Yamaha certainly sounds good for a $30 card, no? I was impressed.

P.P.S. If you can't hear anything and file starts showing up as garbage text in your browser, then your browser doesn't know what to do with MP3s, so just download it (on Windows, right click, Save Target As...) and play it directly.

Home Recording Books and Videos

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