Date: Fri, 14 Feb 2003 09:29:31 -0800 From: Nicholas Esborn <nick@netdot.net> To: Peter B <pb@ludd.luth.se> Cc: freebsd-multimedia@FreeBSD.ORG Subject: Re: Bt878 & whitenoise (some observations..) Message-ID: <20030214172931.GA91411@carbon.berkeley.netdot.net> In-Reply-To: <200302141241.h1ECf8X04143@brother.ludd.luth.se> References: <200302141241.h1ECf8X04143@brother.ludd.luth.se>
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I've seen similar problems with my onboard CMI8738 recently. I didn't notice that it only happened on certain channels, but I didn't try that experiment. I ended up using an SB Live instead. I read somewhere, some time ago, that there was a problem where the CMI driver under FreeBSD wouldn't always initialize at the right clock rate. The result was that sometimes you would get more/fewer samples than you'd expect per unit of time, effectively changing the sampling rate. I'll try to find this again, I think it was on freebsd-multimedia. I think that this would cause noise in ffmpeg, since as I recall, it will truncate the audio data each frame if there's too much of it. This is done in order to maintain A/V sync. I would be interested to know if channels 5, 6, and 10 *always* exhibit the noise across multiple seperate recordings, or if it's intermittent. -nick On Fri, Feb 14, 2003 at 01:41:08PM +0100, Peter B wrote: > > I use FreeBSD-4.7 on a motherboard Asus A7V333 with cpu AMD XP1800, > Brooktree 878 card. The lineout of the Bt878 is connected to CD input of the > motherboard (aux not supported in freebsd4.7?). Programs used is fxtv + ffmpeg. > > I'm experiencing heavy white noise added to recordings done with the builtin > CMedia CMI8738 soundchip. However it only occours on certain TV channels and > won't affect the lineout of the Bt878 (no noise on the stereo). > And can sometimes come and go by restarting fxtv.. :) > > The fenomen is present even if I freeze the picture in fxtv, and use an > audio only record program. > > Anyway I did a table with the fxtv channel number + noise presence. And used > fxtv to tune channel, exit. Start ffmpeg to record. As can be seen channels > with a low frequency is more likely to be affected. > > 5 Noise > 6 Noise > 7 ? (will know in aprox 3 hours, no transmission) > 8 Ok > 9 Ok > 10 Noise > 11 Ok > 12 Ok > 90 Ok > 91 Ok > 92 Ok > 93 Ok > > Anyone know about any interference issues regarding this? > Or maybe there is a bug in the CMI8738 hw/sw ..? > > /P > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-multimedia" in the body of the message -- Nicholas Esborn Unix Systems Administrator Berkeley, California To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-multimedia" in the body of the message
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