[CQ-Contest] Wireless Headphones?

[Jim Brown]

On 11/22/2017 10:11 AM, garyk9gs wrote:
> If you read postings by hams the consensus is that there is too much of a delay, making CW use difficult or impossible.

Latency happens with digital systems, and is greatest with various forms 
of data compression. Latency is simply processing time -- the time it 
takes to convert the analog output of a radio to a digital signal (A/D) 
to be transmitted, the time it takes to convert the received signal back 
to analog (D/A) to drive the headphones. Most consumer digital systems 
use data compression to reduce the required bandwidth, and it takes time 
to compress the data before transmitting it and more time to un-compress 
the data. It also takes time to convert from one digital format (or data 
rate/bit depth) to another.

.wav format files are not compressed, so the only latency is the A/D and 
D/A time. .mp3 format IS compressed, so that time is added. Bluetooth is 
also compressed, and there are several Bluetooth protocols. One of the 
newer protocols has a LOT less latency than older ones.

Systems that are entirely analog have no latency. The oldest wireless 
headphone systems were analog. The audio simply fed an FM transmitter 
and was received by a small FM receiver. Latency is the speed of light 
(damn little). :)

You'll find it impossible to monitor your sending through a signal path 
with even very small latency. Monitoring our own voice starts to get 
uncomfortable with more than about 20 msec; in my sound reinforcement 
work, I've heard very experienced announcers slow down and stop speaking 
with latency greater than 60-80 msec. When you see an artist singing on 
the field in a stadium, they're wearing ear phones that feed them 
undelayed audio of both themselves and their accompaniment. Sound 
travels in air at roughly 1 ft/msec, so it often takes 150-200 msec for 
the sound from the main sound system to reach them.

73, Jim K9YC