www.MarkTAW.com/recording/HomeStudio/Digi001/MeasuringtheDigi001.html (printable version)

I learned about the RightMark Audio Analyzer (RMAA) through Arny Krueger over in rec.audio.pro. Eager to test the Digi 001 I have sitting next to my computer, I decided to install RMAA and see what it said.

From the RightMark Audio Analyzer website:

RightMark Audio Analyzer is an independent audio measurements open- source project developed by iXBT.com / Digit-Life team.

The test suite performs various tests of electroacoustical performance of sound cards and other real-time audio devices. Testing is accomplished by playing the test signals and recording them after they pass through the testing chain.

Normally, you're supposed to punch in a few numbers, slap a few wires in your sound card, and it just runs, but it didn't want to talk nice to the Digi001, so I had to jump through some hoops. I set it to Asynchronous mode. It generated a .wav file, which could then import into ProTools.

Though this isn't the ideal way to test - you're supposed to have a super-flat sound card to do one half of the A/D D/A chain, so you can test each part independantly, but running it through ProTools like this is nice. It gives you a more complete picture of what goes in, what ProTools does to it, and how it comes out.

The first tests I ran at 16/48 were horrible... Maybe I forgot to turn off the light that's on a dimmer, or maybe the card performs worse at 16 bits than it does at 24 bits, but the numbers and graphs weren't very nice.

So I redid the whole test in 24/48. Here's the process I used:

1. I ran the RMAA in asynchronous mode, and it created a 32 bit .wav file.
2. ProTools wouldn't open it, so I took it into Cool Edit Pro and turned it into a 24 bit .wav file. ProTools was OK with this.
3. Then I plugged some Monster Cables into outputs 7 & 8 of the Digi001. Not that I have any special fetish for Monster, but they were handy. I even followed the signal flow arrows, for whatever good that does.
4. Then I looped the 10 foot cable back into the Digi001. First through the line level inputs 7 & 8, and then through the Mic Pres, with the 24dB pad engaged, and the gain set to 12:00. Lastly, I looped it back in through the Mic Pres the same as before, but with the HP Filter engaged (set in the software). 
5. I recorded the results and exported them from ProTools using "Bounce to Disk."
6. Since the RMAA wouldn't read this .wav file, I took it into Cool Edit Pro once again and converted back to a 32 bit file.
7. I opened up RMAA and read the files and exported the results to HTML.

Here are the results.

• Line Level Inputs
• Mic Pres
• Comparison of:
  1. RightMark Supplied "Reference Results 16/48" (Ref1648.sav)
  2. Digi001 Line Level Inputs 24/48 (download .sav file)
  3. Digi001 Mic Pres 24/48 (download .sav file)
  4. Digi001 Mic Pres w/ High Pass Filter Engaged 24/48 (download .sav file)

Here are some notes.

• Because I looped the output of the Digi001 to the input, you're not getting an accurate measure of either individually, but both together.
• The HP filter reading goes above the 0dB line because the 0dB line is an average of the whole line - since so much of it falls below 0dB, the line is raised. Basically, just ignore it's position on the graph and look at the curve.
• Variations in the left/right channel of the Mic Pre measurements are probably caused by differences in the gain level & the random nature of the generated noise.
• That 1 khz spike in all of the graphs is a 1 khz tone in the test file. There is are also a pair of tones around 20khz.

Relevant Links

• RightMark Audio Analyzer
• Digidesign (Digi001)
• Syntrillium (Cool Edit Pro)

Message Board: http://www.marktaw.com/forum/list.php?f=1

page first created on Friday, January 31, 2003

this site and it's contents copyright Mark Wieczorek