Date: Fri, 14 Feb 2003 10:06:59 -0800 From: Orion Hodson <orion@freebsd.org> Cc: freebsd-multimedia@freebsd.org Subject: Re: Bt878 & whitenoise (some observations..) Message-ID: <200302141806.h1EI6x8J033711@puma.icir.org>
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/-- Nicholas Esborn wrote: | 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. Nicholas, just to clarify the deal with the cmi8738 and the clock rate. The problem only manifests itself when setting the clock rate to 44.1kHz. The maximum observed delta is 3%. There is no problem setting other rates. It would depend on how an application dealt with the excess on whether you'd hear it or not (for instance some applications drop repeated pitch cycles in the audio stream and this is inaudible when it works). However it is done, it would almost certainly not manifest itself as white noise. The problem Peter is describing may or may not be due to some analog phenomenon and might be curable by setting all unimportant audio controls to 0 in the mixer. As described the problem not resemble an audio s/w or h/w problem, ie noise on all recordings or on noise on some and not other recordings would point to audio problem. Since the problem as described repeatable on certain channels, it looks more likely that the problem is analog or lies with the tuner, tuner driver, or tuner s/w. - Orion To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-multimedia" in the body of the message
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