[Elecraft] K3 Audio Monitor Delay

[Joe Subich, W4TV]

The delayed sidetone issues are well known in broadcast news 
circles.  They first appeared with satellite circuits where 
the > 250 msec delay gave even the most accomplished speaker 
a stutter.  The problem became even more acute when field 
cueing migrated from analog to digital cell phones and the 
digital processing delis created >100 msec delays on even 
"local" circuits.  The problem has become even more acute in 
the last few years as the microwave equipment used for (local) 
field acquisition has transitioned from analog to digital and 
added yet one more layer of delays.  

In each case, the solution has been to provide mix-minus 
(program audio without the specific remote site audio) and 
add locally generated sidetone at the remote site.  While 
that works, managing a unique mix-minus feed for each source 
(location) in a multi-remote program - particularly when 
"talent" and/or guests at the remote sites must interact - 
is not exactly simple <G>. 

73, 

   ... Joe, W4TV 
 



> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jack Smith
> Sent: Saturday, January 16, 2010 7:12 AM
> To: elecraft at mailman.qth.net
> Subject: [Elecraft] K3 Audio Monitor Delay
> 
> 
> 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=nor
mal&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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