On Monday 13 February 2006 20:06, Matt Ettus wrote: > I seem to remember that the preemphasis on stereo signals is > not performed on the multiplexed signal. It is actually > performed on the audio components separately, before mixing > with the stereo subcarrier. Therefore deemphasis needs to be > done after the stereo part is mixed back down to baseband. > > To me, this is backwards, and is not useful, but I think that > is the standard. Achilleas sent an email to the list several > months ago on this subject. He also had a simple > implementation that did stereo.
Actually it is very useful the way it is. It would be bad to preemphasize the composite signal. To preemphasize the composite in effect converts the system to phase modulation. The subcarrier would then consume most of the bandwidth, and the baseband (mono) would be drastically reduced, resulting in a significant reduction in apparent mono signal to noise ratio. Stereo signal to noise ratio would be about the same as it is now, but there would be no advantage to mono. In the existing system, if stereo SNR is not good enough, you can switch to mono and get almost as good SNR as if stereo wasn't there. "Almost" means about a 6 db degradation, which is due to the fact that baseband modulation must be lowered by that much. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
