Date: Wed, 12 Apr 2000 22:01:49 -0700 From: Tim Pozar <pozar@lns.com> To: Alan Clegg <abc@firehouse.net> Cc: multimedia@FreeBSD.ORG Subject: Re: noise reduction? Message-ID: <20000412220149.B20685@lns.com> In-Reply-To: <20000412223357.C66243@ecto.greenpeas.org>; from abc@firehouse.net on Wed, Apr 12, 2000 at 10:33:57PM -0400 References: <20000412223357.C66243@ecto.greenpeas.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Wed, Apr 12, 2000 at 10:33:57PM -0400, Alan Clegg wrote: > Ok, now that Tim (!!) has gotten most of my problems fixed, I'm to a point > that I'm just about ready. Now I have a running stream, but it has a > constant hiss (I'm assuming from the noisy environment). > > Since the audio input is a radio scanner, there are long periods of what > should be silence. The silence has a hiss. > > Does anyone know of an application that can do real-time "hiss supression"? > I've done as much as I can on the hardware side, putting ferite coils on > the cables. > > I'd like *SILENCE*, not hiss. > > Stream can be heard at: http://www.firehouse.net:8000 The hiss is down a bit. I measure it about 25-30 db down. This hiss is the scanner's squelch not gating all the way. You could run a gate or an expander between the radio and the sound card. This would silence the audio more between transmissions of the fire department. If you are handy with Op-Amps you can do this with a varible gain Op-Amp such as an VCA or perhaps a voltage comparator that only turns on an Op-Amp when it sees a signal. Check out Walter Jung's "Op-Amp Cookbooks" for more details. Couple of comments.... You can get away with a lower sample rate as the bandwidth on public safety two-way is at the most 4Khz. You could sample this at 16Khz. The bit rate could also be reduced to 16 or even 8 Kb/s. You can get away with some more streams that way. Tim To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-multimedia" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20000412220149.B20685>