Thanks to the portability and power of laptop computers, many live sound engineers are now able to carry their own acoustical analysis tools wherever they go. For example, I recently picked up a Pentium 133 sub-notebook in an online auction and, for a $400 investment, now have a useful dedicated platform for both e-mail and SIA Software’s SMAART Pro(tm) FFT measurement software. In “no soundcheck” festival situations, I can set up the system in only a couple of minutes and, using only the break music between acts as a source, can quickly knock the system equalizer into shape before the band goes on. As quickly as I can start the application, plug in the mic, run a cable for the reference signal and set the delay time offset, I’ve got a picture of frequency response.
However, the mic preamps found in most notebook computers are not high enough in quality to use with analysis software. The MP-200 ($349 list) from AudioControl Industrial is a portable 2-channel measurement preamp that offers a neat and economical solution for laptop users. About the size of a paperback book, the MP-200 runs on a 9-volt battery. I’ve been able to use the same 9-volt alkaline battery for a week or more, but I typically use the system only for short sessions at soundcheck and the beginning of the show. Given the vagaries of live sound, I find that after ten minutes of making adjustments, there’s often little more that FFT analysis can tell you about the rig, at least until the weather changes or the audience comes in. But for longer analysis sessions, the MP-200 can also be powered by an external 9-volt “wall wart.”
The small electret condenser measurement mic supplied with the MP-200 (the same one AudioControl supplies with its 3050 RTA) is about the size of an XLR barrel adapter. Each of the MP-200’s two mic inputs has a five-position gain switch with 10dB steps. Channel one is for the first mic input, which is normally the measurement mic. The second channel can be switched between the line input, pink noise or either of the two mic inputs. (Using the reference mic on the second mic input can be helpful for checking the response of another mic plugged into the first input.) The line level input has a continuously variable gain control, as does the pink noise source. Pink noise is on a switching 11/44-inch jack so that it won’t run the battery down when it’s not plugged in, and that comes in handy when there’s no other source of pink noise.
The single line-level input, useful for bringing in the reference signal from a mixing board, CD player or other signal source, is on a pair of summed RCA jacks. I carry a 11/44-inch-to-RCA cable and an XLR adapter; using these, I can get a reference signal out of just about any desk. The MP-200’s two output channels are available on a pair of RCA jacks and on a stereo mini-jack, easing quick connection to a laptop. (Laptops typically offer only stereo mini-jack I/Os.)
The small measurement mic supplied with the MP-200 is not completely flat, a result of low-voltage phantom power. But some FFT software, such as Sound Technology’s SpectraLab, can accommodate mic correction files; an adjustment at the extreme ends of the spectrum at 30 and 10k Hz is suggested. Bear in mind that the extreme ends of the spectrum are not always very important in live sound situations. In any case, the benefits of being able to get an FFT measurement quickly far outweigh this minor flaw.
AudioControl Industrial, 22410 70th Ave. W., Mountlake Terrace, WA 98043; 425/775-8461; fax 425/778-3166; www.audiocontrol.com.