I need to reduce signal level from a 2-ch preamp to a 2-ch power amp. How tight a tolerance do these attenuators maintain?

You will need two of these...one for left and one for right. The tolerance on Shure equipment is tight and professional in tolerances stated. These will work well places between a preamp output and an amplifier line/aux input. When an input is overdriven with too much signal it will distort at any and all volumes...these units allow the preamp to not overdrive the input stage of the power amplifier so that the power amp starts with a distortion free input signal that it can amplify to the speakers.

Can I use this for echo feed back on microphone

the short answer is "no" ummm.... It MIGHT help a little tiny bit, but even if it does help, most humans would not be able to tell. That's not what it's meant for. It's meant specifically to diminish frequencies below 100Hz. Feedback is ALMOST never caused by frequencies below 80hz. In fact, I would actually argue that most feedback is caused exclusively by vocals pushing their own individual signal (or the overall master/bus) over the threshold that allows the mic to "hear itself through the speakers". That means frequencies in the 180ish hertz to 5,000ish hertz(and quite often even higher). Feedback control is more about dynamics and overall volume(particularly on stage), mostly because not many sound engineers or performers care to tune the PA or the room/venue to suppress the resonant frequencies that turn into feedback. Having your main speakers in line with the band/performers/entertainment is also not the most advantageous thing to do for the same reason; the culprit resonant frequencies will start accumulating shortly after your PA is set up. The microphone hears a signal then sends it out through the speakers, which then get picked up through the microphone again, and then back out through speakers. If you have feedback problems, this device MIGHT clean up your overall sound a bit, but will not eliminate feedback. If you want to rid yourself of feedback you should consider; tuning the room/venue with sound absorption, moving your mics closer to their source, having a quiet stage(in ear monitors), or spend lots of money on real nice and smooth main PA speakers and spend decent amounts of time on their placement in that room/venue. Hope that helps.

do i need 2 of these if hooking up to h4n? if not, won't it only record 1 sided?

Short answer would be yes you would need two of these for a full stereo BUT you could use just one of these and then a y cable to feed the or source the one mono signal to both stereo channels so then if you really did not need stereo then one of these and a y cable will yield two channels with same mono audio on each of the two channels and that may be completely acceptable audio as it will sound fine but not be true stereo but will be audio on both channels...Gordon

Will this attenuator cut a line level signal from a consumer device (like a Roku player...-10dB?) to be used as mic level input on a pro mixer?

I believe it'll solve your problem. I am using it to feed the line level input from a Shure wireless mic receiver (line out) to the mic inputs on a Zoom recorder. The line-to-mic feed I've described works like a charm with this adapter. I have a pair of them. Best regards, Bill

Item Weight	90.7 g
Product Dimensions	20.07 x 13.97 x 2.54 cm; 90.72 Grams
Item model number	A15AS
Color Name	#N/A
Connector Type	XLR Connector
Material Type	Alloy Steel
Power Source	Corded Electric

A15AS Switchable Attenuator (15, 20, 25 dB), Passes Phantom Power

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