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  • Microphone Gain / echo cancellation / etc
  • chaos
    Full Member

    Just wondering if the hive mind of STW can help with this.

    I’ve put in a fairly simple video conferencing system for a customer with three meeting rooms in different locations so three units all with extendible microphone widgets that sit in the middle of the meeting room table. H.323 connectivity at the moment though I could use SIP.

    One of the rooms has glass panels on two sides as well as a large glass cabinet on another and a lowish ceiling. What we’re finding is that there is a fair bit of almost echoey noise from that room – not the feedback kind but just a harshness and what might be sibilance if I understand it correctly. It’s better if lots of people in the room but with just one or two it’s quite noticeable.

    Is this the sort of thing Mic Gain should help with as I’m not seeing much difference changing it? Or do they just need to get some softer furniture in e.g. wood table / cabinets / curtains / fabric blinds / etc?

    Free Member

    The additional bodies are diffusing and absorbing the sound and, you’re correct, soft furnishings would do a similar job. You can buy/make attenuation panels too. Adjusting the mic gain just makes the mic more sensitive (effectively) so won’t help, you’ll just get more problems with feedback. The only sure way to deal with it is to get the mics closer to the person speaking, thus eliminating much of the room’s sound.

    Full Member

    ah ok, thanks.
    now need to work on the dropped sound issue but that’s another problem. BT most likely…

    Full Member

    Three Fish has it.

    Having a curtain that can be pulled over one of the large reflective surfaces could cut the reverberation significantly. Finding a solution in the tech side of things will be tricky if not impossible, other than getting people closer to the microphone.

    If there is a single presenter, you could look at using a microphone with a Cardioid polar response, i.e it’s most sensitive to sound hitting it from the front. Strong room reflections come from other directions (generally).

    Conference mics are generally omni-directional and cannot distinguish between what is direct speech sound and reflections of the speech from room surfaces. Hence the solution is to reduce the strength of the reflections compared to the direct sound. The best way to do this is to treat the room or get people much closer to the mic. The former will give the best results, as you’ll have to rely on people to remember to be close to the mic for the latter. (perhaps a much smaller conference table would work for that?)

    Full Member

    Does your conferencing system provide any equalisation adjustment? Your best bet is to kill the reverberations at source as already explained. If this can’t be done, you may be able to reduce the worst parts of the harshness and sibilance by selectively tuning out frequency bands – almost certainly it will be the higher frequency content that you need to reduce. The controls might be labelled as Eq, HF Filter, De-Esser or something similar.

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