Subject: [AVTCORE] Additional use cases for draft-brandenburg-avt-rtcp-for-idms

From: "Kevin Gross" <[email-masked]>
Date: Mon, 15 Aug 2011 18:19:25 -0600

In reviewing the IDMS draft I had volunteered to contribute additional use
cases. I forwarded these to Ray who suggested that I also post them here.

Kevin Gross

AVA Networks

Networked stereo loudspeakers

Because of our ability to localize sound based on inter-aural time
differences, in a stereo listening situation, we are very sensitive to
changes in latency between the two speakers. These changes are perceived as
a shift in or instability of the "sound stage" during critical listening.
These effects are readily noticeable with shifts of 10 microseconds or
smaller. If the individual speakers in a stereo listening setup operate from
independent network interfaces any changing difference in latency between
the two speakers greater than 10 microseconds will be detrimental to the
listening experience.

Conferencing sound reinforcement system

A conferencing sound reinforcement system is used in commercial and
government installations such as legislative chambers, courtrooms,
boardrooms, classrooms (especially those supporting distance learning) and
other such venues. Each participant using such a system has a microphone and
a speaker. There may also be other speakers to provide reinforcement for
non-speaking participants such as in an audience area or jury box. Each
microphone/speaker pair is individually connected to a network and transmits
digital audio to the other devices through the network and receives digital
audio to be reproduced through the speaker over the network. There may be a
central appliance which receives, prioritizes and mixes the microphone
signals. In some systems an individual mix is created for each speaker such
that a speaker's own voice does not come out from his speaker or from those
immediately surrounding him.

The objective of these systems is to provide enough gain to enhance
intelligibility but not so much that the speaker sounds or feels amplified.
Meeting this objective helps insure that natural person-to-person
communication is retained. To this end, it is desirable that the sound
through the system and from the speakers arrive 5 to 30 milliseconds after
the the sound arriving through the air from the person speaking. Delays in
this range invoke the Haas effect which allows listeners to locate the
person speaking based on the sound arriving through the air while the sound
reinforcement system provides the additional gain required to achieve
desired intelligibility. It is also desirable for the sound to come out of
nearby speakers at within 5 milliseconds as longer differential delays will
be perceived as reverberation or echo.

Video wall

A video wall consists of multiple computer monitors, video projectors, or
television sets tiled together contiguously or overlapped in order to form
one large screen.# Each of the screens reproduces a portion of the larger
picture. In some implementations, each screen may be individually connected
to the network and receive its portion of the overall image from a
network-connected video server or video scaler. Screens are refreshed at 60
hertz (every 16-2/3 milliseconds) or potentially faster. If the refresh is
not synchronized, the effect of multiple screens acting as one is broken.

Phased array transducers

Phased array and wave field synthesis techniques are increasingly used in
audio applications. These techniques work by sending or receiving slightly
different versions of a signal in a spacial sampling arrangement to produce
or record spacial and directional sound fields. The individual transducers
in these applications can be extremely sensitive to differential latency.
Example applications include conferencing microphone systems able to
electronically aim at the person speaking to improve signal to noise ratio.
These microphones are also able to report the location of the speaker for
purposes of automatically aiming a video camera at them.

Concert sound systems called line arrays allow technicians control over the
amount of sound sent to different places. People in the front of the
audience can have the same loudness as those in the back. By preventing
sound from reaching the roof and back wall of the performance space, the
amount of reflected sound heard by the audience is reduced and the listening
experience is improved.

In these systems, accuracy in locating or emitting sound is related to
differential latency through basic trigonometry. In these applications,
microseconds of differential latency can translate to degrees of
uncertainty. Accuracy greater than the audio sample period (about 20
microseconds for professional 48 kHz sample rate) is generally desired.