Posted by
Stewart Baker on
Jan 16, 2010; 12:29pm
URL: http://elecraft.85.s1.nabble.com/K3-Audio-Monitor-Delay-tp4403437p4404064.html
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=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
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