While I am sure you have looked at the devices in question, I figure I=20 will mention it for completeness... Do any of the systems (mic receiver, audio amp etc) have a spare=20 output? maybe a headphone or monitor jack or even output for a cassette=20 tape deck? If so, what is preventing you from interfacing directly with=20 that? On 2012-09-19 19:17, V G wrote: > On Wed, Sep 19, 2012 at 4:35 PM, Dwayne Reid =20 > wrote: > >> At 09:38 AM 9/18/2012, V G wrote: >> >> >Currently, lecturers use a radio microphone link that transmits=20 >> audio from >> >a small microphone and transmitter attached to their body to the=20 >> podium, >> >where the audio is received (I assume via a standard 3.5mm jack)=20 >> and sent >> >to the speaker system for amplification. >> > > I'll have to survey this before going any further, so I know exactly=20 > what > I'm dealing with. I have seen 3.5mm line-level devices being used,=20 > but so > far haven't seen any XLR connectors where I'm expecting to tap the=20 > signal. > > >> Audio levels on the lower-cost receivers can be >> all over the place, depending upon who makes the unit. Again, >> though, assume a level somewhere between -40 to -20 as a starting >> point, unless the unit specifically mentions having a line-level >> output. This would then be -10dBv for hobby-grade units or +4dBm=20 >> for >> professional units. >> > > In either case, the professor will adjust his own gain until he's=20 > satisfied > and everyone can hear him speak, so my device shouldn't modify that=20 > in any > way. So at the end of the day, the signal going into the speaker=20 > system in > any given lecture room/microphone device will be at pretty standard=20 > and > predictable levels. I shouldn't have to do any modification of that=20 > signal > at the hardware level at all. > > I believe that you should absolutely transformer-isolate the receiver >> audio from your device. This ensures that you don't introduce >> ground-loops into the existing system. So long as the input >> impedance of the device that you are feeding is a standard 10K or=20 >> so, >> you would have no problems with loading down or otherwise affecting >> the existing Mic receiver audio path. >> > > You're absolutely right, how could I have missed that? The audio=20 > input into > my device should definitely be isolated. > > >> The output of the isolating transformer then feeds whatever device >> you are using to capture or transmit the audio. >> >> FWIW, my company makes an inexpensive audio isolation module that >> would work well for your application. They sell for somewhere near >> Can $25 in small >> quantities. >> < >>=20 >> http://trinity-electronics.com/content/Products/AudioProducts/PBCL475Tra= nsformerIsolatedMonoSumCard/tabid/152/Default.aspx >> > >> . I can also supply the bare transformers if your quantities get >> large enough to justify this - you could then just include the >> transformers on your custom audio capture card. >> >> These transformers are a standard part number but are custom >> manufactured for us only when we place our annual orders (12 week >> lead time). We purchase them by the thousands. >> > > That looks like a really neat module. > > I'll make sure of the audio interfaces being used and post an update=20 > soon. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .