[Elecraft] K3 Audio Monitor Delay

[Stewart]

Very interesting Jack.
I might get round to injecting an audio tone into the mic input 
and measure the delay to it appearing at the TX monitor.

73
Stewart G3RXQ
On Sat, 16 Jan 2010 07:12:07 -0500, Jack Smith wrote:
> 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=norma
l&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
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