On Thu, 23 Jun 2005, Klaus-Peter Junghanns wrote: > Am Donnerstag, den 23.06.2005, 12:41 +0200 schrieb Armin Schindler: > > > > I strongly disagree. :-) You dont want to do echo cancelation in > > > userspace. Especially not on a non-realtime operating system. > > > To make echo cancelation work it has to be as close to the line > > > interface as possible. Also the frames have to be as small > > > as possible. This rules out capi pretty much. > > > > If you don't want echo-canceling in user-space, then neither Asterisk nor > > any chan_* plugin should do it. > > > > I don't know the zap channel code, but does the zap echo-cancel-code is > > inside a kernel module? > > Yes, sir. > > > If yes, then I have to disagree here. Something like 'playing' with > > audio-data is nothing the kernel should be concerned with. > > This belongs in user-space and if you need realtime, then you should use a > > realtime OS or use RT-scheduling. Just putting such a code into kernelspace > > is a bad idea. > > What is so bad about "playing" with audio-data in kernel space?
Besides preemption or RT-patches, it is not easy (and noboady does it) to be 'nice' and have a fair scheduling. With such work in kernel, you just say "I'm at the highest priority, I don't care about others". And that's just wrong in the kernel. Normaly, the kernel just should provide access to the hardware and basic functions for interaction with the hardware. > If you "play" with echo cancelation in user space you will need > to de-jitter the audio first introducing more and more latency, so > your echo cancelation becomes way more computationally expensive. That depends on what scheduling priority this task runs. If you don't want to get interrupted by other tasks, then you need a higher priority. > > So the correct way is either the hardware supports it or the > > application knows what to do with the data received, like DTMF. > > > > Why should the application have to worry about things like echo > cancelation? In the case of Asterisk and echo-cancel, this application is the position where is makes sense. Otherwise you need a copy of the echo-cancel code in each channel driver. > Zaptel is not only used by Asterisk but also by other > projects. With EC in kernel space (which gets switched on and off > by userspace) there is no need to reinvent the EC-wheel for every > project. Okay, from that point of view it makes sense. On the other hand, something like echo-cancel and DTMF is not channel specific and therefore should not be part of that. Or would you add additional codecs into the channel driver? Armin _______________________________________________ Asterisk-Users mailing list Asterisk-Users@lists.digium.com http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
