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Old 08-24-2011, 04:17 PM   #50
synthy
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Join Date: Aug 2011
Location: alessandria, italy
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Quote:
Originally Posted by drumphil View Post
USB is indeed slower than firewire regardless of the difference in their theoretical data rates. The actual data rate isn't that important for most devices however, with USB still having enough real world bandwidth for 24 or maybee more channels of 24/96 audio. The real problem is latency. For whatever reason which I don't understand enough about to explain properly (inefficient system with cpu controlling everything), USB devices to date have never managed to get close to the round trip latency of firewire devices.

Here are the main differences.

FireWire, uses a "Peer-to-Peer" architecture in which the peripherals are intelligent and can negotiate bus conflicts to determine which device can best control a data transfer
Firewire is a peer-to-peer protocol, meaning that every device on a Firewire network is equally capable of talking to every other device. Two video cameras on a Firewire network can share data with each other. A Firewire audio interface could save sound data directly to a Firewire hard drive. Your computer is just another peer on this network, and has no inherent special status.


Hi-Speed USB 2.0 uses a "Master-Slave" architecture in which the computer handles all arbitration functions and dictates data flow to, from and between the attached peripherals (adding additional system overhead and resulting in slower data flow control)

USB devices are asynchronous, which means that any device has the power to send any amount of data at any time. If two devices decide to talk at once, their data can collide with each other. If the traffic is not highly time-sensitive, this isn't a big deal. There are routines in place to manage it, and you'll never notice if your mouse click happens a couple microseconds later. BUT. There are a few applications where it matters, and one of them is audio. An audio interface is sending a constant stream of sound data back to the computer. It rarely uses up the whole pipe, and so it's still possible for other devices to talk but the odds of collisions are higher, and if you get too much other traffic the errors can pile up beyond the computers ability to stay caught up and you lose some sound data.



But the real reason Firewire is more reliable than USB is more fundamental than that. It's because Firewire allows two operating modes. One is asynchronous, as we described above with USB. The other is isochronous mode, and it lets a device carve out a certain dedicated amount of bandwidth that other devices can't touch. It gets a certain number of time slices each second all its own. The advantages for audio should be obvious: that stream of data can just keep on flowing, and as long as there isn't more bandwidth demand than the wire can handle (not very likely) nothing will interfere with it. No collisions, no glitches.
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quelli che... aahhhh l'analogico, e credono di essere in un enorme orologio... tic...tac
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