[Elecraft] K3 Audio Monitor Delay

[Paul Christensen]

> 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..

Typical 80 ms of latency over the Internet is enough to completely render 
ear-to-hand coordination with an iambic paddle as "impossible."  The latency 
is effectively doubled when one considers that it may take 80 ms for the key 
closure to arrive at the transmitter but it takes another 80 ms for the 
transmitter's sidetone to reach the operator at the remote location for a 
net delay of ~ 160 ms.  To the best of my knowledge, this type of "dual 
latency" with CW has not been studied in depth.  Of course, latencies are 
dependent on the IP path.  When operating from my hotel in Italy last year, 
latency was approximately double the worst latencies I've measured in NA.

When using a manual key or paddle, it necessitates the use of a local 
sidetone injected into the headphone audio.  Some of the QSK attributes are 
still possible, only Rx audio between keyed elements appear delayed in the 
headphones.  That's not a problem so long as the locally-injected side-tone 
is synchronized with the sending.

By contrast, I've found when using a CW keyboard from my netbook at a remote 
location, latency is of no consequence since the brain is typing as if 
writing a paper but the brain does not require audio feedback from the 
sidetone to keep the typing synchronized.

Paul, W9AC