I have serious doubts that the filter will do what you want. The human brain is already excellent at discerning speech vs noise when that noise is in a different freq range than the speech. It might make things more pleasing to listen to but I doubt it will take barely intelligible speech and make it clearer. That said, you do want to go active with the filter. RC wouldn't be sharp enough and LC would require large inductor values of reasonable Q. Look up Sallen-Key filters. They are a way to implement a 2 pole arbitrary frequency and Q filter with one op-amp and 2Rs and 2Cs. I think there are online design calculators for this but the basic design process is to choose a filter type (Butterworth would probably be best for you) and order (number of poles) and then tables or calculator will give you where the poles need to be. They will be in complex conjugate pairs and each pair can be implemented with one Sallen-Key section. If odd order, there will be one additional pure real pole which can be implemented with Rs and Cs. Be sure to bear in mind that you need a bandpass filter and not the more common low-pass (or maybe low-pass would be good enough if your mic doesn't have much low freq response) I think the most bang for the buck will be in designing the acoustics of the mic to reduce noise pickup, as you are already doing. On Mon, Jan 21, 2019, 1:09 PM Neil wrote: > Hi all, > > Background: I built a robot that will drive around and chat (remote > operator) with kids in a crowd, but I've been agonizing over the audio, > specifically from the kid (robot-side) to the remote operator. I ran > some tests with a cardioid condenser handheld mic/transmitter (Shure > SM58 FWIW) and it picks up voice well, but I'd like it to get less > surrounding noise. The Shure won't fit eaily inside the robot so > currently looking at just using a condenser element and transmitting > with a Samson Concert 88 TX/RX. > > I'm tinkering with physically directing the noise with pipes/tubes and > will try a parabolic reflector, but I'm also wondering about using a > bandpass filter just after the mic, to be more selective for human > voice. POTS is around 3k bandwidth (300Hz - 3300Hz), which is great for > voice/speech/talking. Would this be an ideal range for limiting speech > frequencies here also? > > For the actual filter, I was thinking about just going passive so I > don't have to worry about split power supplies, but IIRC for something > low-power like this, I should be able to create a virtual ground with a > voltage divider and an op-amp follower. Shouldn't active be better for > this? FWIW, I have 12V available on the robot. > Any other thoughts? Time is of the essence here, so simpler is good, > but it has to work well. > > Cheers, > -Neil > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .