[Elecraft] K3 Audio Monitor Delay

[Jack Smith]

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