USB interfaces- latency, bit dropping ect

robot gigante · 19th June 2003

This came up in a thread on the Apogee Mini Me but it kind of fizzled out, probably because I cut/pasted a big post- whoops sorry.

Anyway I have a couple questions for someone who knows:

Digidesign lists the monitoring latency for the Mbox at 164 samples. Now depending on the amount of information passed via USB, will this change at all, or remain consistent at 164 samples even if the USB bus is choked with more than it can handle(I don't know what the latency is for the MiniMe but assume something similar)?

Bob Ohlsson posted that it is 'legal' for the USB protocol to drop bits(ie. truncate without dither, correct?)- when will this happen? At random?

Thing is, I'm looking into getting a portable MiniMe/MiniDAC combo at some point and it would be nice to know what I'm getting into and whether or not I'll need to get a PCMCIA/SPIDF interface instead of going in USB.

BTW why would Grace and Apogee use USB in the first place, I'd expect that from a cheep Digidesign box, but..?

neilsby · 23rd June 2003

I've found my midiman audiosport duo to be quite heavy on latency. Even at it's lowest setting i can't software monitor.
I haven't noticed any drop-outs or picks in the sound though.

Does firewire address these issues? I was looking at purchasing the motu 828 mkII, but definitely won't if it doesn't address the issues of the usb cable.

How does firewire compare to a traditional pci type soundcard?

robot gigante · 25th June 2003

Bouunce

Neilsby, firewire is much better. MOTU should list the latency spec somewhere, or you could email them. I think you'll be ok with the 828 though.

So no one knows the answers to my USB woes then?

Bob Olhsson · 25th June 2003

The USB spec. permits the use of amazingly cheap hardware that does not handle data reliably without massive levels of buffering and error-correction overhead. While this is ok for consumer products and game machines, it isn't nearly as appropriate for real time data acquisition as most other serial port formats and hardware.

BevvyB · 25th June 2003

Does this mean that the Mini Me is useless for 'playing along to'?

Bob Olhsson · 25th June 2003

Quote:

Originally posted by BevvyB
Does this mean that the Mini Me is useless for 'playing along to'?

It means that your mileage with any USB device could vary widely depending on individual computers, chips and configurations.

robot gigante · 25th June 2003

Thanks for the reply, Bob.

If you have any links to info about some of the problems with USB or care to elaborate any further it will be appreciated.

Quote:

Does this mean that the Mini Me is useless for 'playing along to'?

With the Mbox at least each track will be 164 samples off, so supposedly if you shift the new tracks 164 samples back you will be ok, but I wonder if the amount of latency will fluctuate, which would make that fix useless.

Bob Olhsson · 28th June 2003

A friend of mine was developing a wearable documentation system for the space program. USB looked like a great solution until he looked into the specs of the chips and discovered that spilling bits all over the floor was considered acceptable.

19th June 2003	#1
robot gigante Lives for gear Joined: Feb 2003 Location: out west Posts: 3,994 Thread Starter 3 Reviews written	USB interfaces- latency, bit dropping ect This came up in a thread on the Apogee Mini Me but it kind of fizzled out, probably because I cut/pasted a big post- whoops sorry. Anyway I have a couple questions for someone who knows: Digidesign lists the monitoring latency for the Mbox at 164 samples. Now depending on the amount of information passed via USB, will this change at all, or remain consistent at 164 samples even if the USB bus is choked with more than it can handle(I don't know what the latency is for the MiniMe but assume something similar)? Bob Ohlsson posted that it is 'legal' for the USB protocol to drop bits(ie. truncate without dither, correct?)- when will this happen? At random? Thing is, I'm looking into getting a portable MiniMe/MiniDAC combo at some point and it would be nice to know what I'm getting into and whether or not I'll need to get a PCMCIA/SPIDF interface instead of going in USB. BTW why would Grace and Apogee use USB in the first place, I'd expect that from a cheep Digidesign box, but..?

23rd June 2003	#2
neilsby Gear nut Joined: May 2003 Location: London Posts: 94	latency I've found my midiman audiosport duo to be quite heavy on latency. Even at it's lowest setting i can't software monitor. I haven't noticed any drop-outs or picks in the sound though. Does firewire address these issues? I was looking at purchasing the motu 828 mkII, but definitely won't if it doesn't address the issues of the usb cable. How does firewire compare to a traditional pci type soundcard?

25th June 2003	#4
Bob Olhsson Motown legend Joined: Jun 2002 Location: Songwriter Gulch, Nashville TN Posts: 10,877	The USB spec. permits the use of amazingly cheap hardware that does not handle data reliably without massive levels of buffering and error-correction overhead. While this is ok for consumer products and game machines, it isn't nearly as appropriate for real time data acquisition as most other serial port formats and hardware. __________________ Bob's room 615 562-4346 Georgetown Masters 615 254-3233 Music Industry 2.0 Interview

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25th June 2003	#5
BevvyB Mindreader Joined: Jun 2002 Location: London Posts: 2,604	Does this mean that the Mini Me is useless for 'playing along to'?

28th June 2003	#8
Bob Olhsson Motown legend Joined: Jun 2002 Location: Songwriter Gulch, Nashville TN Posts: 10,877	A friend of mine was developing a wearable documentation system for the space program. USB looked like a great solution until he looked into the specs of the chips and discovered that spilling bits all over the floor was considered acceptable.