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Re: USB vs. FireWire

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Re: USB vs. FireWire

Subject: Re: USB vs. FireWire
From: Herbie Robinson <email@hidden>
Date: Thu, 6 Oct 2005 19:51:07 -0400

At 4:16 PM -0600 10/6/05, Thane Heninger wrote:

Can anyone comment on the preference of USB or Firewire for professional audio?

It would seem that USB is more ubiquitous and with high speed operation, it should work well. And yet, looking in the marketplace, the Edirol UA-101 seems to be the only product that uses USB 2.0 high-speed multi-channel, high frequency I/O. Most products use FireWire.

You also need to consider installed base, momentum, perception and technical appropriateness for the job at hand.

USB 2.0 is far from ubiquitous in the Mac marketplace. The entire product line only got to it very recently and people don't turn over Macs as frequently as PCs. Also, the target market is price challenged (meaning they keep older machines more than other users and they often buy used machines).

Firewire has been around longer; so, there has been more time for vendors to develop IP and for Apple to tune the system for high performance isochronous I/O. It also has been very slow to be adopted for audio; so, there has been a tendency for the main proponents to supply development kits at prices small companies can afford. Also, there have been standards committees working for years, not just on the basics of how to pump the data, but also things like professional level clock synchronization.

The original developers of Firewire audio intended it to be for professional or semi-professional use. The original intent for USB was for things like iMic. USB 1.1 has to be pushed to the limit just to do high quality two channel I/O (without bending the rules). The Firewire bus is still way ahead of the host (in terms of being the bottleneck). There is a lingering perception that Firewire is for professionals and USB is for mom and pop to do video conferencing. It may not be true any more, but an established image is a hard thing to work against. It has been my experience (and just about everybody else's) that USB 1.1 is flaky. That also doesn't exactly make me want to run out and buy a high end device that uses USB 2.0.

And then there is that fact that Firewire is, in theory, better for audio because it is a multi-master bus. It is possible to patch some Firewire audio devices directly to each other without the host computer being involved. Right now, only mLan implements this, but in time, more devices probably will.

Is it because the USB 2.0 Audio spec has not been completed? (Speaking of which, does anyone know when it will be complete? Has it faltered in the committee?) Are there technical hurdles that make it more difficult to bring a USB audio product to market?

Today I watched the replay of the Audio Hardware and MIDI session (205) from the last WWDC. It suggested that USB was for hobbyists and FireWire was for Pro applications. However, it was comparing the USB 1.1 speeds.

One concern we have is for maintaining our clock. Would we have more jitter on USB than FireWire?

I believe USB 1.1 doesn't even specify a way to transmit the word clock and you say 2.0 hasn't come out, yet. I'm not sure the Firewire spec for transmitting word clock is out either. In either case, you shouldn't be deriving word clock directly from the bus clock. It should either be coming from an external signal or derived from a protocol designed to transmit word clock. Every input device that I know of, now, has a word clock input for synchronization purposes; so, I suspect there aren't any standard protocols, yet. Wherever the word clock comes from, it needs to be carefully processes with some kind of PLL to reduce jitter. -- -***************************************** ** http://www.curbside-recording.com/ ** ****************************************** _______________________________________________ Do not post admin requests to the list. They will be ignored. Coreaudio-api mailing list (email@hidden) Help/Unsubscribe/Update your Subscription: This email sent to email@hidden References: >USB vs. FireWire (From: Thane Heninger <email@hidden>) Prev by Date: Re: USB vs. FireWire Next by Date: Re: DLS program change bug? Previous by thread: Re: USB vs. FireWire Next by thread: Re: USB vs. FireWire Index(es): Date Thread