Let me add some quantified data on monitoring delay. In the telephone industry, the signal from the transmitter back to the earpiece is is called "sidetone." In the conventional analog telephone network, sidetone is generated locally in the telephone instrument, but can also come from reflections in the network, called echo, often occurring in 2-wire to 4-wire transitions. Echo suppressors are employed to reduce the reflections because it was quickly learned that delayed echos are disconcerting to telephone users.
With the replacement of analog transmission to digital technology, and in particular speech compression and transcoding required in digital mobile telephone systems, side tone delay and echo control has again become something that equipment and network designers must consider. In any event, the effect of delayed sidetone upon articulation by the speaker has long been studied, and the generally accepted view is that anything more than 50 ms is cause for concern and values exceeding 100 ms are a red flag. (A related topic is overall delay, which causes uncertainty over when one speaker stops and other begins. This is a real problem in tandem satellite links, and even more so when a digital mobile radio system with transcoding and transmission delays are present, to the point where digital mobile telephone switching algorithms usually set the "no satellite flag" to yes.) An excellent summary of the typical research can be found at http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JASMAN0000650000S100S115000006&idtype=cvips&gifs=yes&ref=no, reproduced below. "Sidetone^ delay (delayed auditory feedback) is known to cause speakers to^ talk more slowly, and at delays of about 200 ms^ also causes severe articulation disturbances. If shorter delays can slow^ speech without adverse effects on articulation, this effect could be^ used to make talkers speak more slowly in certain communications^ situations. Subjects read lists of 1, 2, 3, or 4^ syllable words and of sentences under each of 6 delay^ conditions (0, 7.5, 15, 30, 60, and 100 ms). Delays^ of 15--30 ms caused a significant slowdown in speaking rate^ with no adverse effects on articulation. Delays of 60--100 ms^ caused a greater slowdown but also had a noticeable adverse^ effect on speech quality, especially for sentences and polysyllablic lists.^ In communications situations where the quality of transmitted speech is^ degraded (e.g., vocoded speech), sidetone delay may be useful in^ modifying the talk's behavior to improve overall speech quality." Most studies use general population research subjects, but skilled and experienced operators (amateur radio or military) may be able to tolerate greater delays without harmful effect. The general user data suggests that radio monitor delay should be 50 ms or less, with the emphasis on "less." Anyone interested in researching the subject should Google "sidetone delay" or "delayed auditory feedback" and you will find more about the subject than you ever wanted to know. Jack K8ZOA www. cliftonlaboratories.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
