This is an Altec-Lansing active filter or stereo equalizer unit, made in USA. I used this for many years with my home stereo system, but now must sell it. I havent used it for a while, so I tested it before posting it here on EBay, and it appears to work as it should. It has a clear plastic cover which must be removed for access to the band-adjusting sliders. This plastic cover has captured screws, so they wont fall out and get lost when the cover is off. When in place, the plastic cover is not only a nice dust shield but also keeps little fingers off of your carefully adjusted equalization settings. Note that there is no on/off switch, so if the unit is plugged in, its powered up. There is, however, a switch under the plastic cover which puts the equalizer in or out of the circuit. This item comes with spec sheet and operating instructions, and measures 18.5 W x 6 H x 7 D. It stands on four rubber feet and is not directly rack mountable without some type of user modification. There is one caveat: Anytime a unit employs wirewound potentiometers (sliders in this case), they can get dirty or a little corroded and youll get that scratchy sound through the audio system as the sliders are moved. Thats the case with this unit. I bet theres a way to clean these or improve this situation but I never bothered to figure it out. This is something that you may want or need to consider doing if you buy this unit. Heres some information on the specs from the flyer: Each channel (left and right) has 24 active band-rejection filters, so there are 48 total. The filters equalize ISO preferred 1/3-octave center frequencies from 63 Hz to 12.5kHz. Each filter provides up to 14 dB attenuation at the center frequency and is skirted to cross over with adjacent filter sections at -7 dB. Thus combined, the filters produce balanced, smooth response and ripple-free summation through approximately 85% of their adjustable range. A broadband reinsertion gain control is included with each channel. A three-position switch permits switching equalization in or out of the system, or switching to tape machine while maintaining equalization.