Re: [RE] Latencies through RE cables (better URL)
Kevin,
>> I've looked at the scenarios in the paper. I have a couple comments.
>>
>> 1/ No headphone scenarios are considered. A DJ or singer wearing
>> headphones
>> is the most critical case I'm aware of with respect to latency.
>> Delays above
>> 0.5ms are audible and, in many cases, objectionable in this
>> scenario. This
>> sort of headphone monitoring is routinely used in home studio recording
>> (section 1.3.2) and even by some geeky garage musicians (section 1.3.3).
Good points. Could you sketch out the scenario that you want illustrated?
Or, could we simply replace the speaker/air/ear with headphones/ear?
>>
>> 2/ I question whether a 5ms processing delay is achievable
>> through a PC as shown in figure 1.3. The PC architecture was not designed
>> for real-time processing. Delay through a PC is certainly greater than
15ms
>> and can reach
>> 100ms and beyond. As such, some musicians find it unacceptable
>> to run their
>> monitors through the PC; they use external gear to bypass the PC during
>> tracking. Others, baulk at the cost of the external gear, and learn to
>> perform well despite the latency.
Good point. While its theoretically possible to be low latency, reality
is more like you specify. I'll chat with a few others this afternoon,
to sense what is thought appropriate. Its certainly true that a professional
mixer is designed for low latency; a PC is not but can make do...
DVJ
David V. James
>>
>> 2/ I question whether a 5ms processing delay is achievable
>> through a PC as
>> shown in figure 1.3. The PC architecture was not designed for real-time
>> processing. Delay through a PC is certainly greater than 15ms
>> and can reach
>> 100ms and beyond. As such, some musicians find it unacceptable
>> to run their
>> monitors through the PC; they use external gear to bypass the PC during
>> tracking. Others, baulk at the cost of the external gear, and learn to
>> perform well despite the latency.
>>
>> -----Original Message-----
>> From: owner-stds-802-3-re@IEEE.ORG
>> [mailto:owner-stds-802-3-re@IEEE.ORG] On
>> Behalf Of David V James
>> Sent: Tuesday, April 26, 2005 3:52 PM
>> To: STDS-802-3-RE@LISTSERV.IEEE.ORG
>> Subject: [RE] Latencies through RE cables (better URL)
>>
>> All,
>>
>> (The URL has been updated, after David Law
>> provided a more universally accessible web page).
>>
>> Things seem to have been quiet for the last week.
>> Perhaps I could stimulate some discussions on
>> cable latencies?
>>
>> I believe Alexei's presentations have claimed that
>> interactive latencies of 15ms are nearly audible.
>>
>> Since the link delays are only part of the delay
>> equation, this has led some of us to believe that
>> (worst case) per-hop latencies should not exceed
>> 0.5ms. (This number is much more than the speed
>> of light, since it includes buffer and conflict
>> delays.)
>>
>> Is there any controversy with using this as a
>> working per-hop maximum delay number?
>>
>> For background material on this topic, please
>> reference pages 15-17 of the following
>> working paper:
>>
>> http://www.ieee802.org/3/re_study/material/index.html
>> (Thanks again to David Law for his quick posting!!)
>>
>> I have spent the last week accumulating content
>> of various slide presentations into the above
>> listed working paper. Hopefully this will be helpful
>> when considering this and other issues.
>>
>> DVJ
>> David V. James
>>
>>