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

From: "Kevin Gross" <[email-masked]>
Date: Mon, 15 Aug 2011 21:48:19 -0600

In reviewing the IDMS draft I had volunteered to contribute additional use
cases. Ray Brandenberg suggested that I 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.

---

From: "Allison, Art" <[email-masked]>
Date: Tue, 16 Aug 2011 11:06:31 -0400

Mr. Gross,

The timing assertion for Networked stereo loudspeakers is much tighter
that I would have expected. Placement of stereo speakers within a foot
is a normal rule of thumb for the casual listener - and that  is about
1.1ms delta at room temperature. The ' golden ears' do have ability to
detect small differences especially with high attack waveforms, but I
would like to see the study that showed this small time difference. Can
you please provide a cite? 

And I wonder if the system requirement should be based on the smallest
known delta, unless there is no implementation complexity added to
convey the suggested resolution. 

Art Allison 
Senior Director Advanced Engineering, Science and Technology 
National Association of Broadcasters
1771 N Street NW
Washington, DC 20036
Phone  202 429 5418
Fax  202 775 4981 
www.nab.org <blocked::http://www.nab.org>  
Advocacy  Education  Innovation 

From: [email-masked] [mailto:[email-masked]] On Behalf Of
Kevin Gross
Sent: Monday, August 15, 2011 11:48 PM
To: 'IETF AVTCore WG'
Subject: [AVTCORE] Additional use cases
fordraft-brandenburg-avt-rtcp-for-idms

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

Kevin Gross

AVA Networks

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.

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.

---

From: "Kevin Gross" <[email-masked]>
Date: Tue, 16 Aug 2011 11:12:32 -0600

The requirement for the stereo case is specified differently than the
others. The 10 microsecond figure there applies to _changes in latency_, not
static difference in latency described in all the other cases. Tolerance for
static differences for the stereo case are probably on the order of 1
millisecond. The first-order effect of static latency differences is to move
one of the speakers - just depends on how fussy you are about real vs.
effective speaker placement.

The 10 microsecond figure is conservative (I've heard anecdotal claims of 1
microseconds sensitivity) and derives from our ability to accurately locate
sounds based (in part) on comparison of arrival times at each ear. The 10
microsecond figure is not difficult to derive/check. It is also not
difficult to set up a listening test to see what your own threshold is.
Here's a quick reference on it - http://www.cs.ucc.ie/~ianp/CS2511/HAP.html
(see Localisation of Sound Sources section)

Throughout, I've tried to use what I consider reasonable and verifiable
requirements figures. Some will always seem to argue that they need better
performance.

Kevin

From: [email-masked] [mailto:[email-masked]] On Behalf Of
Allison, Art
Sent: Tuesday, August 16, 2011 9:07 AM
To: IETF AVTCore WG
Subject: Re: [AVTCORE] Additional use cases
fordraft-brandenburg-avt-rtcp-for-idms

Mr. Gross,

The timing assertion for Networked stereo loudspeakers is much tighter that
I would have expected. Placement of stereo speakers within a foot is a
normal rule of thumb for the casual listener - and that  is about 1.1ms
delta at room temperature. The ' golden ears' do have ability to detect
small differences especially with high attack waveforms, but I would like to
see the study that showed this small time difference. Can you please provide
a cite? 

And I wonder if the system requirement should be based on the smallest known
delta, unless there is no implementation complexity added to convey the
suggested resolution. 

Art Allison 
Senior Director Advanced Engineering, Science and Technology 
National Association of Broadcasters
1771 N Street NW
Washington, DC 20036
Phone  202 429 5418
Fax  202 775 4981 
 <blocked::http://www.nab.org> www.nab.org 
Advocacy  Education  Innovation 

From: [email-masked] [mailto:[email-masked]] On Behalf Of Kevin
Gross
Sent: Monday, August 15, 2011 11:48 PM
To: 'IETF AVTCore WG'
Subject: [AVTCORE] Additional use cases
fordraft-brandenburg-avt-rtcp-for-idms

Kevin Gross

AVA Networks

Video wall

Phased array transducers