Raymond Chandler wrote: > What's interesting to me is.... everyone on this thread except you has > said that in real-world scenarios, they need the EC for reliability. > One of which, does signal processing programming professionally. It > seems to me that if you "build a better mouse trap" you must know what's > involved in making it work properly. I'm not sure what your background > really is, but you'd be hard pressed to match up to Steve's reputation > and/or experience. > Public willy-waving is undignified but, in brief, I've built and sold IVRs since 1997, wrote a CAPI-based soft IVR in 1999 (which required software for, inter alia, DTMF detection), developed a software fax modem (V.29, V.27ter, T.30, etc.) which I sold to a CTI card vendor and so on.
I've collected some data, of which it is commonly said that the plural of anecdote - which is what we've had so far - is not. The IVR collects a 16 digit DTMF string, terminated by #. TDM->IP conversion was performed by an Asterisk box with an el-cheapo quad E1 card (no EC) for half the calls, and an AS5400 (with EC) for the other half. The proportion of entries missing one or more digit was 3.1% (Asterisk) and 3.3% (AS5400); this is not a statistically significant difference given the sample size. The reason for looking at this criterion is (a) that it's easy to measure, and (b) the most likely way that a DTMF detector will fail in the presence of excess noise, which includes echo, would be to miss a digit. This error rate is the sum of human error + detector error, and I've no measurements to show how this might be split; I would expect it's almost all human. Note that this is a digit error rate of about 1 in 500. This is, of course, only data from one site, but it's a start; it's only by collecting data such as this that one can understand how well one's mouse trap works and whether it needs improvement or not. > That said, it might be a good idea to just agree to disagree as this is > starting to sound like the faxing over IP talks I hear a lot. (i.e. > "faxing over g.711u with no t.38 works fine for me") Where it might work > for some people by some mysterious phenomena, it won't work for the > general public. And telling people that they don't need EC, where so > many have already said that they obviously do, is just as irresponsible, > IMHO, as you claiming Steve was for telling them that they don't need it. > That's a simplification. Simple IVR (record, replay, collect DTMF) probably doesn't need EC; if you're trying to do ASR with barge-in, bridge callers to other callers or operators, etc., then you probably do. I am interested that the recommended solution is 'buy Sangoma' - expensive and proprietary - when Oslec, a FOSS echo cancellers which, by all accounts, works extremely well, is out there and has been for some time. --Dave _______________________________________________ Freeswitch-users mailing list [email protected] http://lists.freeswitch.org/mailman/listinfo/freeswitch-users UNSUBSCRIBE:http://lists.freeswitch.org/mailman/options/freeswitch-users http://www.freeswitch.org
