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| Thread ID: 36646 | 2003-08-15 06:52:00 | OT - Inverting signal | somebody (208) | Press F1 |
| Post ID | Timestamp | Content | User | ||
| 167976 | 2003-08-15 06:52:00 | I have built a little wired comm system for a concert I'm running next week - so I can give cues to followspot operators etc. However, the mics from the headsets are picking up too much background noise - especially loud bands. I figured that if I could somehow generate an inverting signal of the background noise, I could get it to cancel out. Does anyone know where I could find a circuit of this sort? Or where I could hire a device which would do this (in the Hawkes Bay area)? |
somebody (208) | ||
| 167977 | 2003-08-15 09:23:00 | You mean noise cancellation cicuitry . Its not easy, as "inverting" needs to take all the phase shifts into account . It can be done, but its a highly complex process . Commercially available headphones use the process (I have used them on International flights in Business Class) but they cost hundreds each . It requires a microprocessor to analyse the signals (probably using Fourier analysis) driving a variable phase and amplitude amplifier . Expect to spend lots . |
godfather (25) | ||
| 167978 | 2003-08-15 09:55:00 | Thanks godfather. I might have to re-think the idea, or just learn to put up with the ambient noise. | somebody (208) | ||
| 167979 | 2003-08-15 10:13:00 | You need to have low sensitivity mics, and have them close to the operators mouths to avoid your present problem. | godfather (25) | ||
| 167980 | 2003-08-15 10:29:00 | Ok . The problem is that i've already bought the headsets, which are standard computer headsets from Warehouse Stationary . I built the electret microphone powering circuit which I asked about on this forum earlier this year, and that seems to work quite well . Would adjusting the gain/levels on the mixer (which I'm using to connect the headsets) help in any way? |
somebody (208) | ||
| 167981 | 2003-08-15 10:33:00 | reduce the gain as much as possible in the mic circuits. Unfortunately electret mics tend to be quite sensitive, but somewhere you will find a better setting. Or turn down the band amplifiers.... |
godfather (25) | ||
| 167982 | 2003-08-15 10:56:00 | I'll have to do some rewiring - I am currently plugging the mics into a line-in socket, opposed to a mic socket. That means that I have to turn the gain almost right up, in order to pick up the sound. If I did some rewiring, and plugged it into the mic-in socket, then that should help, and give me some more flexibility. Would that have a risk of blowing up the mixer? | somebody (208) | ||
| 167983 | 2003-08-15 11:16:00 | How would you "blowup" the mixer? Drive it into distortion, yes . Unless you are going to put some serious voltages (which shouldn't even exist in your system) it would be a poor mixer that could be "blown up" in such a manner . Most audio preamps would just be driven into clipping and distorton but never destroyed . You have an impedance and level mismatch at present, which will not be helping your problem . Mic into a mic level input will help . |
godfather (25) | ||
| 167984 | 2003-08-15 22:29:00 | Thanks for your help Godfather. | somebody (208) | ||
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