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updated May 03, 2008
My experience with the new PreSonus AudioBox has been, at best, rather disappointing. I'm now on my second AudioBox, and still not getting the audio quality that I need. I used to have a Sound Devices USBPre, but foolishly sold it a few months ago. So, now I'm hunting for a replacement for the USBPre. The first AudioBox (Serial Number U208030093) that I bought was absolutely terrible! The recorded audio was full of USB data noise... you could even hear a data buzz as the USB mouse moved. I contacted PreSonus, and they promptly replaced that noisy AudioBox. The new replacement AudioBox (no Serial Number) is certainly much better, but it still has quite a few problems and annoyances. The AudioBox is fairly attractive cosmetically, it's a nice size for portable field use, and the product's shipping box was nice looking too, but other than that, the AudioBox has been, for me, a rather disappointing product.
There's quite a bit of low frequency noise and a small spike of 1 KHz USB data noise, but this noise level is of no practical concern when using relatively noisy small diaphragm condenser microphones such as my AT-4041. Here's a sample with no input signal (XLR pin 2 has 150 ohms to ground, XLR pin 3 has 150 ohms to ground, no phantom power):
However, when using an unbalanced input (to simulate my unbalanced stereo Audio Technica AT-822) there's a huge amount of low frequency noise plus an easily audible 1 KHz whine (plus harmonics) in the recorded audio. Here's a sample with no input signal and an unbalanced input impedance (XLR pin 2 has 150 ohms to ground, XLR pin 3 is tied to pin 1 ground):
Here's a plot of the same AT-822 with 220 ohm resistors to ground as the "cold" (XLR pin 3) mic input on each XLR:
I've tested the AudioBox on three different computers (an HP laptop, a Dell laptop and a Dell desktop) and the audio noise was similar on all three machines. When using a pair of fully balanced AT-4041 mics and phantom power, there's not any noticeable USB data noise, and the mysterious low frequency noise is significantly reduced. With the AT-4041 balanced mics, the ambient noise in this room (which is primarily computer fan noise peaking at 240 HZ) looks like this :
Comparison Plots: For comparison, here are some plots from a Mackie 1402-VLZ routed to a cheap $30 sound blaster card via a 6 foot long unbalanced 1/8" stereo mini-plug cable. This is not a particularly sophisticated setup, and is shown here as an example of what one might expect from a relatively mediocre system. First a sample with no input signal to the Mackie 1402-VLZ (150 ohm input resistors, balanced)... note the 60Hz harmonics due to ground loops:
2) Mic Gain -- gain can't be turned down far enough: That front panel graphics indicate that the range of the mic gain control knob is 0 db to 60 db. But that's clearly not true. The actual range of the mic gain control seems to be only a total of about 35 db, and in fact the mic gain cannot be turned down far enough to avoid clipping with my AT-4041 mics at a normal distance from an acoustic guitar. For those mics, another 10 db of gain reduction would be necessary to avoid clipping. That's a serious problem. 3) Headphone Monitor -- it's in mono not stereo! Gees, the headphone monitor of the inputs is in mono! How bizarre. Stereo monitoring is really very important to me so that I can quickly hear any mic or cable problems before recording. Perhaps that's a "feature" for someone using a mic
in one channel and an instrument in the other channel, but for me,
it's just another problem. 4) Headphone Monitor -- whining noise Near the min and max positions of the headphone monitor gain, there's a slight audible whine. Without the phantom the whine is1 KHz (and harmonics), and when the phantom supply is turned on an additional whine a little above 2 KHz may show up. It's not very loud, just enough to be annoying.
I thought that I'd be able to send the output of my Mackie mixer into the AudioBox at line level rather than using the cheap sound card in my computer... but, apparently not. The AudioBox PDF manual says: Both channels of the AudioBox USB have a Mic/Line connector using the Neutrik Combo connector. which initially sounds great since they used the word "line", but alas, then they go on to explicitly say: Plugging a line level source into the instrument inputs on the front of the AudioBox USB not only risks damage to these inputs but also results in a very loud and often distorted audio signal. (In other words, don’t plug a line level source into the combo jacks of channel 1 or 2.). Arrgg... I really need line level inputs. Oddly, PreSonus do not provide any numerical specification of the maximum permitted instrument input level. It would be nice if PreSonus would reconfigure the instrument
inputs to accommodate line level inputs, and publish
specs for the maximum input level (at minimum gain) before clipping occurs. 6) Audio Level Indicator -- help arrives too late There are two clip LEDs on the front panel, one for each of the two audio channels, but they are essentially useless. First of all, the LEDs only light at (or very near) the audio clipping point, which is not very useful, because if you ever allow any clipping of audio peaks, you'll hear some raspy distortion. That is, by the time these LEDs blink, the recording is already messed up. So, what a user really needs is some way to know that the peak audio level is a few db, say -6 db or even -12 db, below clipping for good recording quality. Sadly, the AudioBox does not offer any pre-clip indicators. It would be much more useful if the existing LEDs came on
around -6 db below clipping, or even -12 db. 7) Audio Level Indicator -- not very bright Additionally, the clip LEDs are very, very dim for brief peaks, and for use in anything other than a very dimly lit room, the LED blink may not even be noticed. Clearly the LEDs need some sort
of pulse stretcher, either analog or digital, to assure that the LED blink is easily seen. 8) Phantom Power -- No Indicator: There's no indicator light for the phantom power, which is especially scary with microphones that may be completely destroyed by inadvertent application of phantom power (such as my favorite Audio Technica AT-822 stereo mic). A phantom power LED would be a nice feature. 9) Phantom Power -- Too Easy to accidentally hit the Switch: Additionally, the phantom power button is very easy to bump accidentally. For mics using phantom power, this will only result in the mic being turned on or off, but for mics that may be completely destroyed by phantom power (such as my favorite Audio Technica AT-822 stereo mic) inadvertent application of the phantom power could be disastrous. A recessed
switch would be a really nice feature. 10) AudioBox Unable to Record with Windows Vista: Although the AudioBox was successfully found by Windows XP as a recording device, the Vista audio control panel does not show any AudioBox recording capability. Vista does shows AudioBox as a playback device, and playback works ok, but there is no AudioBox recording capability shown. Adobe Audition 3, indicates the presence of the PreSonus ASIO driver, but when the ASIO driver is selected, it always causes an error message saying "You have selected a driver for an ASIO device that is not available". I tried uninstalling and reinstalling the PreSonus drivers, but that didn't fix anything, so I've not been able to record anything whatsoever from the AudioBox using Vista. Hmmm... this problem is more than an annoyance. Not being able to
record anything is a rather severe problem. 11) Incomplete Software Uninstaller: I uninstalled the PreSonus AudioBox drivers from my Vista machine, and found that after running the uninstaller, there were still dozens of PreSonus entries littering the registry. Unfortunately, many uninstall programs fail to do a good job of cleaning up after themselves, and that seems like sloppy work to me.
So by now you're probably wondering if I can find anything good to say about the AudioBox... well, sort of. The AudioBox is a nice size for portable use, the front panel, with white graphics (and totally incorrect input gain scales) on blue brushed anodized aluminum is very attractive, the metal knobs have a very nice feel, and the metal sideplates look nice too. But, on the other hand, the top cover (and bottom... but who cares about the bottom) is a rather tacky looking piece of sheetmetal with exposed screw heads. That's a pity... they almost made something really nice looking.
Perhaps these annoyances wouldn't even be considered as problems by somebody else. I really don't know. Nonetheless, this has been a step-by-step review of what I've personally encountered when testing the AudioBox. Apparently I haven't found a replacement for my old USBPre...
Richard Shelquist
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