On Wed, Feb 15, 2012 at 5:47 PM, David Rowe <da...@rowetel.com> wrote: > [snip] > > As we are looking at push to talk applications, we can tolerate a fair > bit of delay. So we could interleave a few 100ms of Codec 2 frames to > helps us ride over short fades.
I completely agree that many PTT applications can tolerate significant delay such that the increased latency caused by using "super-frames" (multiple frames packed together) would be acceptable. We do that now with other codecs by packing multiple speech frames into a single RTP (UDP/IP) packet to reduce the overhead of the packet headers. Unfortunately, it also increases the penalty when a packet is lost (and lost packet concealment doesn't work well for such big gaps). Making the codec aware of the "super-frame" would present some opportunities for optimization beyond what is possible just by packing in multiple frames as we do now. As you mentioned, in the RF case it helps with interleaving/FEC. It also provides the perfect framework for delta-coding all but the first frame. I can't think of any disadvantage of using such delta-coding in the IP case (where received packets are guaranteed not to have any bad bits because such packets are completely dropped). In the RF case, it could make a single bad bit have an effect on multiple frames. That could potentially be compensated for by using the bits saved by delta coding for extra error correction; I don't know if that would be a net gain or not. > In line with the voice-SMS ideas Codec 2 offers another way to use voice > in low SNR channels. It could be transmitted at any bit rate in > non-real time then played back. For example 1200 bit/s coded speech > could be sent at 300 bit/s, then playback in real time. This would mean > waiting 40 seconds to receive 10 seconds of speech, but might be useful > for some applications. Agreed. In cases similar in concept to SMS, rather than thinking about a low bit rate for the transport (300 bits/s), it is a question of how much speech you can pack into a fixed-size (and cost) message. Short messages could be coded at a higher quality without increasing the transport cost; larger messages (up to a point) could be compressed more highly to make them fit. > Thanks, > > David Steve --- Steve Strobel, KC7HXB Link Communications, Inc. 1035 Cerise Rd Billings, MT 59101-7378 (406) 245-5002 ext 102 (406) 245-4889 (fax) WWW: http://www.link-comm.com MailTo:steve.stro...@link-comm.com ------------------------------------------------------------------------------ Virtualization & Cloud Management Using Capacity Planning Cloud computing makes use of virtualization - but cloud computing also focuses on allowing computing to be delivered as a service. http://www.accelacomm.com/jaw/sfnl/114/51521223/ _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
