Subject: RE: [AVT] Re: Layer 2 clock sync [was: AVT draft agenda]

From: "Miller, William C" <[email-masked]>
Date: Thu, 26 Oct 2006 16:23:31 -0400

Chuck is absolutely right. Latency is critical in any live application,
including where a performance is recorded live for later broadcast. For
talent to be able to use video or audio for cueing, latency must be kept
to an absolute minimum.  Cell phone end-to-end latencies, for instance,
are typically at or beyond the threshhold of usability, even for dialog
cueing.  

For the application cited (miking a drum kit) differential latencies in
the microseconds are required. For monitoring, I agree that 2 ms total
latency is about the absolute limit.  For this reason, I expect analog
RF technologies to prevail in these applications.

Best regards,
Bill Miller

William C. Miller
ABC-TV
 
212-456-4448 phone
212-456-2284 fax
[email-masked]

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
lazzaro
Sent: Thursday, October 26, 2006 3:43 PM
To: Chuck Harrison
Cc: [email-masked]
Subject: [AVT] Re: Layer 2 clock sync [was: AVT draft agenda]

On Oct 26, 2006, at 11:29 AM, Chuck Harrison wrote:

> The delays between sampling and packet transmission
> (whether they arise in the OS, the hardware, or whatever) are simply 
> part of the transmission jitter/delay budget and are irrelevant to the

> precision of the end-to-end system. Especially so in recording-system 
> or one-way scenarios where latency bounds can be extremely relaxed.

Performers on stage are typically using monitoring systems (in-ear, or
speakers in front of them on the floor or a stand).  So, the latency
from the wireless mic, through the mixing console, and back up to the
stage is critical, and can't be relaxed -- 2 ms would make many but not
all performers happy (vocalists in particular are very sensitive to this
-- especially using in-ear).

Likewise, using these networks as the first-hop for long-distance
network musical performance systems are also an application where every
millisecond counts.

So, I'm wary of declaring this effort to be latency relaxed ... for some
applications it isn't.

---
John Lazzaro
http://www.cs.berkeley.edu/~lazzaro
lazzaro [at] cs [dot] berkeley [dot] edu
---

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

---

From: Chuck Harrison <[email-masked]>
Date: Thu, 26 Oct 2006 13:54:08 -0700

> Chuck is absolutely right. Latency is critical in any live

Actually, it's John Lazzaro you're quoting there. But I agree,
he's absolutely right.

And I think it's an attractive challenge to see how close to
traditional analog performance we can come. As AES42 shows, you
only have to pay a sub-sample-time latency penalty for going
digital. But packetizing (e.g. onto Ethernet) always adds a
delay penalty. Doesn't have to be a lot!

Peace,
  Chuck